Unit 1 Biology

Chapter 3

Composition of cells

Chapter breakdown

• Water• Organic compounds

- CHOs, proteins, lipids, nucleic acids• Minerals• Vitamins• Enzymes• Photosynthesis• Cellular respiration• Levels of organisation

Compounds of cells

• Water is the most abundant compound in our bodies, making up 60% of males and 50% of females.

• Water is the major component of cells (70%)• Water serves a number of important functions:

- many organic compounds need water for chemical reactions

- water molecules are cohesive (stick together)

- water is a versatile solvent

Water and chemical reactions

• Metabolism includes the sum of all of the chemical reactions in the body.

• Catabolism – the breakdown of compounds to release energy.

• Anabolism – the synthesis of new compounds from simpler ones.

• Because water is the predominant solvent in the body and, as many organic compounds dissolve in water, metabolism occurs in a watery solution

= water facilitates metabolism

Water molecules are cohesive

• Water, commonly known as H2O is comprised of:

- two positively charged hydrogen ions and

- one negatively charged oxygen ion• Each hydrogen atom is linked to the oxygen atom by a

strong covalent bond.• Individual water molecules are highly attracted to each other

(cohesive) due to the negatively charged oxygen being attracted to the positively charged hydrogen. The bond between water molecules is called a hydrogen bond.

Water is a versatile solvent

• The charge of the ions in a water molecule give water the property to dissolve many substances, e.g. Salt (NaCl)

- refer to Fig 3.6 page 54.

How does water dissolve NaCl?

• Substances that dissolve readily in water (salt) are called hydrophilic, while those that do not dissolve in water are called hydrophobic (fats).

Water is the major component of cells

• Fig 3.7 page 55

Answer QC questions 1-3 on page 55

Organic compounds

• Organic molecules are often large molecules made up of smaller sub-units called monomers.

• Many monomers bonded together make up a polymer.

The organic molecules we will be looking at are:

Compound common name

Monomer Polymer

Carbohydrates Sugars/monosaccharide Polysaccharides

Lipids Fatty acids Fats, lipids, oils, waxes, membranes

Proteins Amino acids Proteins

Nucleic acids Nucleotides Nucleic acids

Carbohydrates (CHO’s)

• The basic unit of any CHO is a sugar molecule called a monosaccharide, the most common being glucose.

• Monosaccharide's combine in different ways to form polysaccharides.

• A sugar that contains one or two monosaccharide’s are sometimes called simple sugars, while those with three or more are referred to as complex carbohydrates.

• Cellulose and glycogen are two types of polysaccharides that differ because of the way in which the glucose molecules are linked together (refer to Table 3.3 page 56).

Carbohydrates are important for energy in plants and animals, and also provide structure for plants.

Proteins

• Proteins are the polymers which are made up of building blocks called amino acids (aa’s).

• All amino acids contain the compounds nitrogen, carbon, hydrogen and oxygen.

• There are 20 naturally occurring amino acids (Appendix B)• Two aa’s are held together by a peptide bond, and a chain of

aa’s makes up a polymer – a protein.• The different proteins are made up by different aa

sequences:

each individual protein has a

different amino acid sequence

Refer to Fig 3.10 page 58

Lipids

• Lipids is the general term describing fats, oils and waxes.• Fats and waxes are generally solid at room temp, while oils

are liquid at room temp.• All fats have little affinity for water – they are hydrophobic.• A fat molecule is made of two different kinds of molecules

- fatty acids and- glycerol.

• Triglycerides have a single glycerol molecule • and three fatty acid chains (tri = three)• Phospholipids have a single glycerol molecule • and two fatty acid chains. They are a major • component of cell membranes.

Nucleic acids

• There are two kinds of nucleic acids:

1. Deoxyribonucleic acid (DNA) – located in chromosomes in the nucleus of eukaryotic cells. Each nucleotide unit has:

- a sugar (deoxyribose) part,

- a phosphate part and

- a N-containing base.

The four different N-containing bases are adenine (A), thymine (T), guanine (G) and cytosine (C).

Nucleotides join together to form a chain, and the complimentary pairing of nucleotide bases of two chains form a DNA double helix

Refer to Fig 3.12 on page 59, 3.13 and 3.14 on page 60.

DNA

RNA

2. Ribonucleic acid (RNA) – also a polymer of nucleotides, but different to DNA in three main ways

a) the four bases for RNA are A, G, C and uracil (U),

b) it is an unpaired strand of nucleotide bases, and

c) it exists in three forms:

i) messenger RNA (mRNA) – formed against DNA as a template

ii) ribosomal RNA (rRNA) – together with special proteins makes ribosomes found in the cytosol

iii) transfer RNA (tRNA) – carry amino acids to the ribosomes where they can be made into proteins

The three different forms of RNA are folded in different ways.

Minerals and vitamins

• Minerals are inorganic ions required by both animal and plant cells.

• Plants and animals cannot manufacture minerals, but many of them are extremely important.

How are minerals obtained by

a) animals?

b) plants?• Vitamins are organic compounds that occur in minute

quantities in food that are required in varying quantities by animals.

• Vitamins can be divided into two groups based on their chemical composition: 1) Fat-soluble and 2) Water soluble

• Vitamins are essential for many of the chemical reactions that occur within cells.

Enzymes

• Enzymes are protein molecules that increase the rate of chemical reactions that occur within organisms.

• Enzymes can either be intracellular (used within the cells that make them) or extracellular (they are secreted by cells and act outside those cells).

• The compound being acted on by the enzyme is called the substrate, and each substrate has a specific enzyme – this is because the shape of the enzyme and substrate fit together like pieces of a puzzle.

• Enzyme names are usually related to the substrate they act upon – e.g. lipase acts on lipid, and protease breaks down proteins, amylase breaks down starches (sugars)

• When fitted together, they form an ‘enzyme-substrate complex’ according to the popular ‘lock and key’ theory.

• The rate of enzyme activity is affected by various factors such as temperature, pH, enzyme or substrate concentration.

• Some enzymes require other factors (e.g. vitamins) before they act. In this case, the other factor is referred to as a co-enzyme.

• QC questions 4-7 page 60 and 8-10 page 65.

Enzyme models

• The ‘lock and key model’ is a well known theory used to explain enzyme function.

• It is based on the idea that there is one enzyme for every substrate – enzymes are substrate specific.

• Another model is the ‘induced fit model’, which as the name suggests, implies that enzymes change shape to fit into the substrate.

Producers and photosynthesis

• Using the energy from sunlight, plants, algae and some protists can make organic molecules such as sugars, by photosynthesis.

• These organisms are called autotrophic as they are able to make their own energy. Other animals that cannot make their own energy need to obtain this energy from the food that they eat. These organisms are heterotrophic.

• In photosynthesis, light energy is transformed into chemical energy stored in sugars.

• The simplified, balanced chemical equation for photosynthesis is:

chlorophyll

6CO2 + 6H2O C6H12O6 + 6O2

carbon dioxide water sunlight glucose oxygen

• Chloroplasts are made of folded inner membranes stacked as flattened discs called grana, filled with a fluid called stroma.

• Chloroplasts are the specialised organelles found in plants that contain chlorophyll – the green accessory pigment that plays the major role in trapping light.

• There are other types of pigments, accessory pigments involved in trapping light in different wavelengths.

The inputs for photosynthesis are

- light energy,

- carbon dioxide and

- water

The outputs for photosynthesis are

- glucose and

- oxygen

Accessing energy: cellular respiration

• Although plants can make their own glucose, they need to convert it to a simpler form to be able to be used by the cells.

• Glucose is converted to adenosine triphosphate (ATP) in the mitochondtria via the process of cellular respiration.

• ATP is the energy form used by cells for all cellular processes, muscle contraction, nervous tissue, manufacturing chemicals etc.

• The transfer of chemical energy from glucose to ATP occurs through a coupling of chemical reactions:

• The process of energy transfer from glucose to ATP is not 100% efficient, rather only 40% efficient.

• The remaining 60% appears as heat energy – living cells produce heat as a bi-product of cellular respiration.

• There are two types of cellular respiration:

1. Aerobic respiration – involves the use of oxygen, and yeilds 36 molecules of ATP per molecule of glucose.

2. Anaerobic respiration – occurs in the absence of oxygen and only yields 2 molecules of ATP per molecule of glucose. The end products are lactic acid and CO2.

Levels of biological organisation

Questions

• Biochallenge

Questions 1, 3 and 4 page 72

• Chapter Review

Questions 2, 3, 5, 6 and 9.