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Higher Biology Course Unit 1
Higher Biology
Unit 1
Cell Biology:Cell structure in relation to
function
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Higher Biology Course Unit 1
• In a multicellular (many-celled) organism the cells are organised into tissues.
• A tissue is a group of similar cells which work together to carry out a specific function.
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Higher Biology Course Unit 1
• Some tissues have only one type of cell (e.g. muscle). Other tissues have several types of cells (e.g. phloem contains sieve tubes and companion cells).
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• The structure of a cell is related to its function (what the cell does).
• In a unicellular (one-celled) organism (e.g. amoeba, paramecium, euglena or yeast) all the processes necessary for life are carried out in a single cell.
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Higher Biology Course Unit 1
Paramecium
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Euglena
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Higher Biology Course Unit 1
Root hair
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Leaf epidermis
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Phloem
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Xylem
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Leaf mesophyll
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Parenchyma
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Lining of kidney tubule
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Return
Lining of trachea
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Lining of trachea
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Lining of mouth
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Bone cell
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Higher Biology Course Unit 1
Fat cell
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Higher Biology Course Unit 1
Red blood cell
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Muscle Cell
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Nerve cell
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Cell Ultrastructure
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Cell Boundries
• Cell wall
• Outer boundary of plant cells• Made of cellulose fibres in layers• Strong, slightly elastic• Absorbs water, providing a pathway
for water movement through plant tissues.
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•Plasma membrane
• Forms the cell membrane and forms or surrounds all cell organelles.
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• Made of a double layer of phospholipid molecules with protein molecules embedded.
• Called “fluid-mosaic” model because
1. Molecules move around like fluid2. Proteins form a pattern on surface
(mosaic)
• Some protein molecules enclose a pore through which small molecules can pass in/out of the cell.
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Functions of the plasma membrane
Molecules can enter or leave a cell, across the membrane, in 5 ways:
1. Diffusion2. Osmosis3. Endocytosis4. Exocytosis5. Active Transport
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Diffusion
• Movement of molecules of (gas or) liquid from an area of high concentration to an area of low concentration down a concentration gradient.
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Higher Biology Course Unit 1
• The concentration gradient is the difference in concentration between two areas.
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Molecules cross the plasma membrane in two ways:
• Through the phospholipid layer• Through pores in the protein
molecules
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Osmosis
• Diffusion of water molecules
• Through a selectively permeable membrane (e.g. plasma membrane)
• (S.P. Membrane is a membrane with pores which allows small molecules to pass but not large ones)
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• Water moves from a high water concentration to low water concentration
HWC LWC
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Effects of osmosis on cells
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Hypotonic – higher water concentration
Hypertonic – lower water concentration
Isotonic – same water concentration
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Turgid – cell swollen with waterFlaccid – cell limp through loss of waterPlasmolysed – in Plant cells, water loss
causes cytoplasm to shrink away from the cell wall.
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Endo- and Exo-cytosisCells sometimes take in, or expel, large
quantities of material by forming a “pocket” in the membrane.
This is called endocytosis (taking material into the cell) or exocytosis (materials leave the cell).
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An example of endocytosis is:
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Phagocytosis
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In this form of endocytosis the cell engulfs solid particles (e.g. amoeba) – like “eating” a bacterium.
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Active Transport
Movement of ions across the plasma membrane against the concentration gradient
i.e. Low concentration → High concentration
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Energy is needed.
Protein molecules transport ions across the membrane.
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IN
OUT
Low conc. outside the cell
High conc. inside the cell
Low conc. inside the cell
High conc. outside the cell
Energy
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Essay question
Discuss the role of the plasma membrane under the following headings:
1. The structure of the plasma membrane (4 marks)
2. The role of the plasma membrane in transport (6 marks)
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Discuss the role of the plasma membrane under the following headings:1. The structure of the plasma membrane (4 marks)2. The role of the plasma membrane in transport (6 marks)
Plasma membrane:• Composed of phospholipid bilayer (two layers)• Contains proteins.• Some proteins form pores through the membrane.• Described as a “fluid mosaic”Role of plasma membrane:• Diffusion + movement of liquid/gas from area of high conc. to area
of low conc.• Osmosis + movement of water from area of HWC to area of LWC.• Endocytosis + description of engulfing a large molecule.• Phagocytosis is an example of endocytosis (eating bacteria).• Active transport + movement from area of low conc. to area of high
conc.• Active transport requires energy and a carrier protein.
1 mark for each bullet point. TOTAL 10 Marks
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Higher Biology Course Unit 1Lives in the sea Lives in fresh water
Ion Fresh water
Sea Water
Lobster Mussel Cray-fish
Frog Fresh WaterM
ussel
Na 0.24 478.3 530.9 79 212 109 15.6
K 0.005 10.1 8.7 152 4.1 2.6 0.5
Ca 0.67 10.5 15.8 7.3 15.8 2.1 6.0
Mg 0.04 54.5 7.6 34 1.5 1.3 0.2
Cl 0.23 558.4 558.4 94 199 78 11.7
SO4 0.05 28.8 8.9 8.8 - - -
Concentrations in mM per kg
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In the example above, the lobster actively transports sodium inwards (higher concentration in the body than the sea water), actively transports magnesium out (lower concentration in body than sea water), but does not regulate chloride (concentration equal).
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Higher Biology
Unit 1
Cell Biology:Photosynthesis
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Absorption, reflection and transmission of light by a leaf
Light shining on leaf (100
%)
12 % of light
reflected
5 % of light
transmitted
83 % of light absorbed but only 4 % of this is used for
photosynthesis
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Light absorption by leaf pigments
Leaves contain several coloured pigments of which chlorophyll is the most important.
These pigments absorb light energy.
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Which wavelengths of light are used
White light is made up of several different wavelengths of light from 400 nm to 700 nm.
Normal spectrum of white light:
violet blue green yellow orange
red
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• Collect a leaf and cut into small pieces.
• Add some propanone and sand into a mortar and pestle.
• Grind this up, until the propanone turns green.
• Filter the mixture into a test tube.• Hold the spectroscope up towards the
test tube and look towards the light.
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violet blue green yellow orange
red
violet blue green yellow orange
red
Spectrum viewed through Chlorophyll
The blue and violet are no longer visible and only some of the red is still seen. These have been absorbed by the chlorophyll.
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The main wavelengths absorbed are violet and blue, and some red.
These are most important wavelengths for a plant in photosynthesis.
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Absorbtion and Action Spectra
A leaf contains several pigments which can be separated by chromatography.
The main pigments are:1. Chlorophyll a (blue-green)2. Chlorophyll b (yellow-green)3. Carotene (yellow)4. Xanthophyll (yellow)
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An absorption spectrum shows the absorption of light of each wavelength by each pigment.
An action spectrum shows the rate of photosynthesis at each light wavelength.
Comparison of absorption and action spectra reveals a close match – this is good evidence for the importance of leaf pigments in photosynthesis.
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The presence of several pigments increases the range of wavelengths the plant can make use of.
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Separation of photosynthetic pigments by thin layer
chromatography
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Name Rf value
Carotene
Chlorophyll a
Chlorophyll b
Xanthophyll
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Chloroplasts
The main pigments (chlorophyll a+b, carotene and xanthophyll) are contained in the chloroplasts.
Lamella
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Chloroplasts have:
• A double plasma membrane• A liquid stroma• Stacks of flattened membrane bags
called grana (singular – granum) which contain chlorophyll
• Connecting tubes between grana called lamellae.
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Chemistry of photosynthesis
Remember Standard Grade:
Carbon dioxide + water + light energy → glucose + oxygen
This takes place in 2 main stages:1. Photolysis (needs light)2. Carbon fixation (Calvin cycle)
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Photolysis
Happens in the GRANA of the chloroplasts.
Light energy is absorbed by chlorophyll and used to split water molecules into hydrogen and oxygen.
Energy is released.
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WATER
ENERGYOxygen Hydrogen
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These products are treated like this:
OXYGEN – released as a by-product.
HYDROGEN – attached to a hydrogen acceptor molecule (NADP) to form NADPH2
ENERGY – stored as ATP
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The hydrogen and the ATP play an important part in the second stage of photosynthesis, called CARBON FIXATION.
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Lamella
2
3
4
5
6
Quick Quiz
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1. Carbon dioxide + water + light energy → glucose + oxygen
2. Grana/Granum3. Outer membrane4. Lamellae5. Inner membrane6. Stroma7. Grana8. Water split to hydrogen & oxygen, energy released9. Picked up by NADP to form NADPH2/Picked up by
hydrogen acceptor10. In ATP
Answers
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Carbon Fixation
Takes place in the STROMA of the chloroplast.
Molecules of carbon dioxide diffuse into the chloroplasts where they attach to molecules of 5-carbon Ribulose biphosphate (RuBP)
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The resulting 6-carbon compound is unstable and breaks down into two molecules of 3-carbon glycerate-3-phosphate (GP).
In the next step, GP is reduced to triose phosphate (3-carbon) by the addition of hydrogen (from the NADPH2) and energy (from ATP).
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CO2 (1C)
RuBP (5C)
6C unstable 2 x GP (3C)
Triose phosphate (3C)
NADPH2
NADP
ATP
ADP + Pi
Glucose
Complex carbohydrates + other organic molecules
CALVIN CYCLE
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Triose phosphate has two possible fates:
1. Synthesis of glucose (6 carbon) which is then built up into other carbohydrates (e.g. starch and cellulose)
Plants also use carbohydrates to make other organic molecules (e.g. proteins, fats and nucleic acids)
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2. Conversion to RuBP so that more carbon dioxide can be taken up.
The cycle of reactions involved in carbon fixation is know as the calvin cycle.
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Limiting factors
A limiting factor is a factor which slows down the process of photosynthesis if is in short supply.
Limiting factors are light intensity , carbon dioxide concentration and temperature.
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30°C
20°C
10°C
Carbon dioxide concentration
Rate of photosynthesis
A
B
B
B
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At point A: Rate of photosynthesis depends on carbon dioxide concentration, regardless of temperature.
Carbon dioxide is the limiting factor.
At point B: Further increase in CO2 has no effect. The rate of photosynthesis is increased by raising the temperature.
Temperature is the limiting factor
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Carbon dioxide concentration
Rate of
photosynthesis
Light intensity
Rate of
photosynthesis
Limiting factor = CO2 conc.
Limiting factor = Light intensity
Limiting factor either Light or Temp
Limiting factor either CO2 or Temp
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Aerobic Respiration
Unit 1: Higher Biology
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Energy storage in the cell
Chemical energy is stored in cells in molecules of ATP (Adenosine Tri-Phosphate).
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(Pi = Inorganic phosphate)
In order to release the chemical energy, the bond attaching the third phosphate is broken (shown in red).
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ATP formation
A molecule of ATP forms when a molecule of ADP (Adenosine Di-Phosphate) joins with an inorganic phosphate.
The energy required to join the Pi to the ADP comes from the chemical energy released from the breakdown of glucose during respiration.
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The conversion of ADP to ATP is called Phosphorylation.
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Summary
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Aerobic respiration – S-Grade
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Chemistry of Aerobic respiration
Aerobic respiration is the complete oxidation of molecules of glucose to release energy.
Oxidation is the removal of hydrogen with the release of energy.
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Aerobic respiration takes place in 3 stages:
1. Glycolysis2. Kreb’s Cycle 3. Cytochrome system.
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Stage 1: Glycolysis
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Glucose molecules (6 carbons) are broken down into 2 molecules of 3-carbon molecule called Pyruvic acid.
Happen in the cytoplasm.
No oxygen is required.
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There is a net gain of 2 ATP molecules.
Hydrogen is released and temporarily attached to a co-enzyme carrier molecule called NAD.
NAD + 2H NADH2 (reduced co-enzyme)
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Stage 2: The Kreb’s Cycle
a.k.a. The Citric Acid cycle OR Tri-carboxylic acid (TCA) cycle.
This takes place in the mitochondria.
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Mitochondria
Mitochondria (singular = mitochondrion) are sausage shaped organelles surrounded by a double plasma membrane.
The centre of the called the Matrix and is filled with fluid.
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The inner membrane is folded into cristae which provide a large surface area for the stalked particles on which the cytochrome system takes place.
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• The pyruvic acid diffuses from the cytoplasm into the mitochondrion.
• In the matrix, the pyruvic acid is converted to a 2-carbon compound called acetyl Co-A, releases CO2 and hydrogen. The hydrogen is bound to NAD.
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• Acetyl Co-A now enters the Kreb’s cycle by combining with a 4-carbon compound to form 6-carbon citric acid.
• Citric acid is then broken down in a series of oxidation reactions to the original 4-carbon compound and the cycle begins again.
• The Hydrogen which is released binds with NAD.
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Stage 3: Cytochrome system
• This takes place on the stalked particles on the cristae.
• Hydrogen is released from the NADH2 and passed along a “chain” of hydrogen carriers called the cytochrome system.
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• As each pair of hydrogen atoms are passed along the chain enough energy is released to make 3 molecules of ATP. This is called oxidative phosphorylation.
• At the end of the chain the hydrogen combines with oxygen to form water.
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Production of ATP
• Complete oxidation of one molecule of glucose produces 38 molecules of ATP (36 from oxidative phoshorylation in the cytochrome system and 2 from glycolysis).
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As the organism respires it uses oxygen (and produces carbon dioxide which is absorbed by the sodium hydroxide). This causes the liquid level to rise and the syringe is used to find the volume of oxygen consumed.
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Anaerobic respiration
Aerobic respiration only occurs if oxygen is available to accept the hydrogen at the end of the cytochrome system.
If no oxygen is available anaerobic respiration occurs.
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During anaerobic respiration Glycolysis occurs as normal, but there is no Kreb’s cycle.
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Glucose Pyruvic Acid Kreb’s cycle
ANIMALS PLANTS
Lactic Acid Ethanol + CO2
Oxygen available
Oxygen not available
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Aerobic respiration
Anaerobic respiration
Oxygen required?
Total ATP production (per glucose molecule)
Other products (plants)
Other products (animals)
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Anaerobic respiration is animals occurs during heavy exercise. After exercise stops the lactic acid can be converted back to pyruvic acid by repaying the “oxygen debt” by breathing heavily. It is therefore REVERSIBLE.
Anaerobic respiration is plants is IRREVERSIBLE as the CO2 diffuses out of the plants.
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Measuring the rate of aerobic respiration
The rate of aerobic respiration can be measured using a respirometer.
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Parts of this apparatus have the following purposes:
Glass beads: They are a control to show how it would be with something that does not respire.
Water bath: keeps the test tubes at a constant temperature, as the volume of gas would increase if the temperature increased.
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Syringe: It measures the volume of oxygen used, by pushing down and returning the dye to the same level as before.
Sodium hydroxide: Absorbs carbon dioxide.
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Synthesis and release of proteins
Higher BiologyUnit 1
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Proteins
DNA
Replication
Transcription
Translation
Secretion
C,H,O,NGlobular
Fibrous
synthesis
Double helix
NucleotideGenes
Chromosomes
SugarPhosphate
Base
A,T,C,G
A-TC-G
DNA Polymerase
Genetic code
Golgi body
Rough ER
mRNA
UracilSingle stranded
RibosomestRNA
Codons
Amino acids
Peptide bonds
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Structure and variety of proteins
• Proteins are composed of the following elements:• Carbon, Hydrogen, Oxygen, Nitrogen,
(often Sulphur) = HONCS• Atoms of these elements form amino
acids (20 different ones).• Amino acids link by peptide bonds to
form polypeptides.• Polypeptides link up to form Proteins.
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Role of proteins
TYPE ROLE EXAMPLES
Globular Enzymes
Structural
Hormones
Antibodies
Fibrous Make hair and nails
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Role of genes
• Chromosomes consist of many genes. These carry out their instructions by producing enzymes. Enzymes are made of protein.
• So, genes produce protein; Like this:
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Protein Synthesis
• Genes contain a chemical code.
• This code is part of a molecule of DNA (Deoxyribonucleic acid).
• The structure of DNA enables the correct amino acids to be assembled in the correct sequence to make a particular protein.
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Structure of DNA
• A DNA molecule is made of 2 chains of nucleotides.
• Each nucleotide contains:1. A deoxyribose sugar molecule2. A phosphate molecule3. A base molecule
Phosphate
Base
Deoxyribose sugar
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Phosphate
Base
Deoxyribose sugar
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• There are four different bases, and therefore four different nucleotides:
Adenine nucleotide
(A)
Guanine nucleotide(G)
Thymine nucleotide(T)
Cytosine nucleotide(C)
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• Nucleotides are linked together by means of chemical bonds between phosphate and sugar molecules – called “sugar-phosphate bonds”:
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• Two of these nucleotide chains are joined by means of hydrogen bonds between bases.
ADENINE always bonds with THYMINECYTOSINE always bonds with GUANINE
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• The two, linked, nucleotide chains are twisted into a coil called a double helix.
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• Each chromosome consists of one double-helix shaped molecule of DNA containing many thousands of base pairs.
• A gene is a section of DNA molecule whose base order forms the code to make one protein.
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Replication of DNA
• Chromosomes must be able to copy themselves so that cells retain the same genetic information after cell divisions.
• This copying of the DNA in the chromosomes is called replication.
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• Replication requires:(a)A DNA molecule(b) unattached nucleotides of 4 types(c) enzymes (DNA polymerase)(d) energy (in the form of ATP)
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• Replication takes place in these stages:1. DNA uncoils2. The hydrogen bonds between bases
break (starting at the end like a zip)3. Free nucleotides attach to exposed bases4. Sugar-phosphate back bone reforms
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The Genetic Code
• Proteins are made of a long chain of amino acid molecules.
• A gene contains a code (order of DNA bases) to ensure that the amino acids are joined in the correct order to make a specific protein.
• The order of the bases is called the genetic code.
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• This is a triplet code because the sequence of three bases is needed to code for each amino acid.
• e.g. • AAG codes for amino acid Phenylalanine• GAC codes for amino acid Aspartic Acid• GGA codes for amino acid Glycine.
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So a DNA strand with base sequence:
Would code for (part of) protein:
(one protein molecule may be hundreds or thousands of amino acids long)
A A AAG G GG C
A A AAG G GG C
Phenylalanine Aspartic acid Glycine
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RNA (ribonucleic acid)
• Protein synthesis takes place on the ribosomes in the cytoplasm.
• The instructions in the genetic code are carried from the DNA (in the nucleus) to the ribosomes by a molecule of messenger RNA (mRNA)
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• RNA differs from DNA in 3 ways:
1.RNA is single stranded
2.RNA contains ribose sugar
3.In RNA the base thymine is replaced by Uracil
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There are two types of RNA:• Messenger RNA (mRNA) which
carries the genetic code from the DNA in the nucleus to a ribosome in the cytoplasm.
• Transfer RNA (tRNA) which carries amino acids to the ribosomes for assembling into polypeptide chains.
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Transcription
• The piece of DNA containing the relevant gene uncoils and the base pairs separate.
• Complementary RNA nucleotides then attach to the exposed DNA bases.
• They link together (ribose-phosphate chemical bonds) to form a messenger RNA (mRNA) molecule.
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A T T
C
GA
G G T C A C T A T A G G CT
AC
G
C G G A
T A AG
CT
CC A G T G A T A T C C G
AT
GCG C C T
DNA strand
One gene
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Ribosomes and rough endoplasmic reticulum
• Ribosomes are:• Found in all cells• Free in cytoplasm or attached to rough
endoplasmic reticulum• Spherical, with two halves• Site of translation of mRNA into protein
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Ribosomes
Sheets of endoplasmic reticulum
Fluid filled cavity between sheets
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Assembling the protein = translation
• In the cytoplasm are molecules of transfer RNA (tRNA).
• These are composed to one triplet of bases and an amino acid molecule.
• e.g. Alanine Leucine
• Codon: triplet of bases on mRNA• Anti-codon: Complementary triplet of
bases on tRNA
G C A C U G
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Stage 1
Stage 2
Stage 3
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• The mRNA attaches to a ribosome.
• The ribosome moves along the mRNA with successive codons entering the “active site”.
• Here, a tRNA with the appropriate anti-codon is attached.
• Adjacent amino acids then link up by a peptide bond to form a polypeptide and eventually a protein.
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Secretion of proteins
Nucleus
Nuclear membrane
Pore
Rough endoplasmic reticulum
Ribosome
Golgi Apparatus
Vesicle
Cell membrane
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• The golgi apparatus is made up of many flattened fluid filled sacs.
• Vesicles containing newly made protein are pinched off the rough endoplasmic reticulum.
• These move towards the Golgi and use with the outermost sac.
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• The contents then move down through the golgi from sac to sac, becoming modified in the process.
• The finished product (e.g. glycoprotein), in a vesicle, leaves the golgi and moves to the cell membrane and discharges its contents out of the cell.
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Cellular Defence Mechanisms
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Virus Structure
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Reproduction of viruses
Viruses can only reproduce inside the cells of a host organism.
They use the host’s nucleotides for replication and the host’s amino acids to construct protein coats.
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Defence against viruses
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First line of defence
Mechanisms by which our bodies attempt to prevent entry of harmful microbes.
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Second line of defence
Mechanisms by which our bodies attempt to kill harmful microbes which have succeeded in entering.
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Immunity
Immunity is the ability of an organism to resist disease. The blood is usually involved.
There are two types:1. Non-specific immunity (phagocytosis)2. Specific immunity (antibodies)
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1. Non-specific Immunity
Provides protection against a wide range of invading microbes e.g. by phagocytosis carried out by white blood cells.
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Read page 70 of Torrance and make your own notes on “Phagocytosis”.
Then:• Prepare a 2-3 min illustrated presentation
to give to the class on the topic, explaining:
• How invading bacteria are detected• How invading bacteria are engulfed• What a lysosome is, what it contains and
what it does• What pus is
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Higher Biology Course Unit 1
Phagocytosis
Phagocytosis is the process by which foreign bodies such as bacteria are engulfed and destroyed.
Cells capable of phagocytosis are called phagocytes.
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Higher Biology Course Unit 1
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Higher Biology Course Unit 1
A phagocyte detects chemicals released by the bacterium and moves up a concentration gradient towards it.
The phagocyte adheres to the bacterium and engulfs it into a vacuole formed by an infolding of the plasma membrane.
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Higher Biology Course Unit 1
Lysosomes fuse with the vacuole and release their enzymes into it.
The bacterium becomes digested and the breakdown products are absorbed by the phagocyte.
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Higher Biology Course Unit 1
During infection hundreds of phagocytes migrate to the infected area and engulf many bacteria by phagocytosis.
Dead bacteria and phagocytes often gather at a site of infection forming pus.
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Higher Biology Course Unit 1
2. Specific immunity
A specific invading particle (e.g. A virus) is attacked by a specific defending chemical.
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Higher Biology Course Unit 1
Antigen: a complex molecule recognised by our body as alien (e.g. A virus coat particle).
Antibody: a chemical produced a lymphocyte white blood cell to destroy antigens.
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Higher Biology Course Unit 1
How antibodies work
An antibody is a Y-shaped molecule:
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Higher Biology Course Unit 1
The binding sites on the arms attach to antigen molecules making them harmless:
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Higher Biology Course Unit 1
There are many types of lymphocyte, each type targeting one antigen with specific antibodies.
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Higher Biology Course Unit 1
Types of specific immunity
(a)Active immunity:We produce our own antibodies by:(i) Suffering from the disease and
retaining the antibodies in the blood – (natural)
(ii)Receiving a vaccine of treated antigen (e.g. Empty virus coats) which triggers antibody formation – (artificial).
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Higher Biology Course Unit 1
(b) Passive immunityWe receive ready-made antibodies from:(i)Mother, across the placenta – (natural)(ii) Another mammal (e.g. A horse) which
has made the antibodies in response to treatment – (artificial).
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Higher Biology Course Unit 1
Rejection of transplanted tissues
Make your own notes from Page 73 of Torrance.
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Higher Biology Course Unit 1
Cellular Defence Mechanisms in Plants
Plants defend themselves from attack by:
(a) Producing toxic compounds(b) Isolating the infected area or
infectious organism
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Higher Biology Course Unit 1
(a) Production of toxic compounds
(i) Cyanide• Made by clover plants by a process
called cyanogenesis.• Cyanide works by blocking the
cytochrome system of e.g. Slugs• It is produced when non-toxic
glycoside and an enzyme are mixed as a result of leaf damage.
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Higher Biology Course Unit 1
(ii) Tannins• Tannins are toxic to micro-organisms• They defend by preventing pathogens
e.g. Fungi from gaining access to the plant organ under attack.
• The tannins act as enzyme inhibitors.• Therefore, they interfere with the
invading pathogen’s metabolism and render it harmless.
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Higher Biology Course Unit 1
(iii) Nicotine• This is toxic chemical produced in the
root cells of tobacco plants and transported to its leaves.
• Since it is poisonous it protects leaves against attack by herbivorous insects.
• Nicotine can be extracted from tobacco plants and used as an insecticide.
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Higher Biology Course Unit 1
(b) Isolation of the problem
(i) Insect galls• When a parasite penetrates the
cuticle of a leaf, the leaf produces a gall in response to a chemical stimulus.
• A gall is an abnormal swelling of plant tissue resulting from active division of cells at the site of the injury.
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Higher Biology Course Unit 1
• The combination of the extra layers of cells and rich deposits of tannin in a gall provides the plant with a protective barrier where the parasite can be isolated.
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Higher Biology Course Unit 1
(ii) Resin• Resin is a sticky substance produced
by many trees.• When a plant becomes wounded by a
pathogen the resin-secreting cells increase in activity, trapping pathogens.