BIOLOGY AS LEVELREVISION 01

2. Cell Structures

Cells

ALL organisms are made up of cellsSimplest collection of LIVING matterCell structure correlate to their functionsAll cells are related to earlier cells that they

descend from

MICROSCOPY

Microscopy

Microscope is an instrument that magnifies objects too small to be seen, producing an image that appears larger.

Photographs/ pictures of cells derived from the microscope - Micrographs

Magnification

A measure how much larger a microscope can cause an object to appear

The Ratio of the object to its actual size (Magnification = measured length[of image]/ actual length of object)

Resolution

A measure of clarity – the smallest distance by which two points can be distinguished in an image.

Limited by the physical properties of light

Light Microscope

Commonly used Visible light passes through

the specimen Bent through the lens

system – producing magnified image

X1000 magnification Uses blue light – 400 nm Lowest Resolution = 200nm

The Electromagnetic Spectrum

The resolution depends on the wavelength of the light/ radiation being used on the specimen

Light Colors

Light with the largest wavelength is red = 700 nm

Light with smallest wavelength is blue = 400 nm

With the magnification, resolution is actually half the wavelength

Light microscope uses blue – 200 nm resolution

Electron microscope

Uses electron – has a shorter wavelength

X-ray is hard to control – electron can be controlled using magnets

Electron can only function in vacuum – oxygen molecules may cause the electron to be knocked around

False-coloring by computer

SEM

Scanning Electron microscope

Electron bounce back and forth across specimen’s surface

Creating a detailed 3D image

Resolution smaller that TEM

TEM Transmission

Electron Microscope Electron passes

through the surface Used to inspect the

inner structures of cell

Resolution can go down to 0.5 nm

Light Vs. ElectronSimilarities Both uses

Lens

Differences One uses visible light, another uses electron

molecule (electron vs. photon) Resolution, one is 200, the other is 0.5 With SEM – 3D image is possible Electron is more expensive One focuses light with lens, the other focuses light

by electromagnetic control One uses electron gun, the other uses low voltage

bulb On magnifies up to 1500, the other up to 500000 One uses air as medium, another uses vacumm

Cell Fractionation

Takes cell apart and separates organellesCells are centrifuged where the heavier

components will sink to the bottomUltracentrifuges – fractionates them into

components

Cell Sizes/ Scale

Red Blood Cell: 7 micrometer (7000 nm) Egg cell: 100 micrometer (100000 nm) A virus: 20 – 400 nanometer Prokaryote: 0.1 – 5 micrometer (100 – 5000 nm) Nucleus: 6 – 7 micrometer (6000 nm) Ribosomes: 25 nanometer Cell Membrane: 7 nm Microtubules: 25 nm Microfilaments: 6 nm

Extra read: http://peer.tamu.edu/curriculum_modules/Cell_Biology/module_1/whatweknow.htm

Kingdom of living things

Eukaryote1. Animal2. Plant3. Fungi4. Protists Prokaryote1. Bacteria2. Archea

PROKARYOTEVS.

EUKARYOTE

Prokaryotic

Prokaryote – a simple organism e.g. BacteriaNo nucleusNo membrane-bound organellesHas Cell WallsHas Circular chromosomesCommon cell structures: Plasma membrane,

Cytoplasm, DNA, Ribosomes

Animal Cells

Animal Cell Structure

Nucleus: Contains chromosomes/ DNA – code for the synthesis of proteins that control the function of the cell – hence the nucleus commands the cell

Cell Surface membrane: Holds the cell content, controls the ins/outs, structural forms, cell recognition, adhesion, signaling, transport of substances, endo/exocytosis

Cytoplasm: the liquid where all the cell metabolic activities take place

Mitochondria: Produces energy in the form of ATP through respiration

Animal Cell Structure

Ribosomes: Receiving mRNA coded for Protein synthesis

Lysosome: Engulfs materials and destroy them with enzymes

Rough ER: Has ribosomes on it – involved in protein synthesis – transport network for protein

Smooth ER: Synthesis of lipid – involved in cell detoxification

Golgi bodies: Process the finished proteins

NucleusDouble nuclear envelope –

encloses/ protect DNANuclear pore – received

substances for DNA Replication(extra phosphate), exits for mRNA

small molecules pass through by diffusion, large ones get in actively

in micrographs – RNA/protein complex can be seen plucking the pore

NucleusNucleoplasm – contains

chromatin granules, DNA/associated proteins: during cell division, they condense to form chromosomes

Nucleolus – produces rRNA part of ribosomes, proteins, coenzymes, enzymes for nucleic acid synthesis, RNA

Outer membrane continuous with ER – easier transport

Endoplasmic Reticulum

A system of hollow tubes/ sacs – transportation purpose

nucleus

Rough Endoplasmic Reticulum

Smooth Endoplasmic Reticulum

Rough ER

Covered with ribosomes Interconnected system of

flattened sacs Ribosomes on surface

synthesize proteins which are then transported through the interconnected system

RER is abundant in cells which needed to produce a lot of proteins for exports e.g. Digestive enzymes/ growth

Smooth ER Lacks ribosomes A system of interconnected

tubules Carbohydrate/ lipids

metabolism Synthesizes: triglycerides,

phospholipid, cholesterol Modification of steroid

hormones High percentage in cells

involved with metabolism of lipids/drugs

Golgi Body

Flattened cisternae Invaginate/ fuse to form

vesicles Internal transports by

vesiclesVesicles protect

molecules In case of enzymes –

protect the cells

Cell Membrane Fluid mosaic bilayers which surround the cell

content Control the ins/outs of the cell Gives the cell stability during temperature changes Endocytosis/ exocytosis Important in cell recognition Cell signaling Cell adhesion

CytoplasmMakes up of liquid: CytosolWhere the metabolism takes placeContains water/ solutionMost organelles float hereOsmoregulation

MitochondriaDouble Membrane – isolate

certain reaction – high concentration of enzymes/ substrates can be maintained

Outer membrane – permeable to salt, sugar, nucleotides

Inner membranes – selectively permeable (control chemical composition of the matrix – optimizes enzyme activity)

Mitochondria

Porins on inner membranes – entry of oxygen/pyrovic acid – exit of ATP/ Carbon dioxide

Folded inner membrane (cristae) – increases surface area for enzymes/ coenzymes

70s ribosomes – protein manufacturingLoop of circular DNA – codes for proteinEnzymes

Endosymbiosis theory

States that mitochondria’s ancestors were bacterial ingested by a eukaryote

The eukaryote kept it as it is useful for respiration

Evidences: 70s vs. 80s ribosomes

Evidences: Own DNAEvidences: Divides by

itself

Ribosomes

2 subunitsMade of rRNA/ Protein rRNA – formed in nucleus

– moves out via poresProtein part – assembled

in the cytoplasmFound as dense clusters

(polysomes)On membranes of RER

Lysosomes

Vesicles that contains hydrolytic enzymes

Break down old organelles – recycle the materials

Break down storage molecules

Break down whole cell when it dies

Cytoskeleton

Microtubules – tubulin proteins : Thickest fo the three – around 25 nm

Microfilaments – actin proteins Intermediate filaments

Microfilament

Rods of about 7nm in diameterMade up of a twisted double chain of actin

subunits

Microfilaments

Create tensionSupport the shape of the cell3-D Cortex inside plasma membraneBundles of microfilaments indie the microvilli

Microtubules

Microtubules

25 nm wideMade up of tubulin proteinsArranged in dimers (alpha tubulin/ beta

tubulin)This dimer repeat in vertical format – forming

a protofilament 13 protofilaments arrange around a hollow

coreMICROTUBULES FORM

Microtubules

Shapes the cellGuide the movements of cells/ organelles –

with help of motor proteinsMake up spindles that separate chromosomes

during cell division

Centrosome

Contains 2 centriolesThe location for MTOC (Microtubules

organizing center)MAY have a role in regulating the cell

division

Centrioles Microtubules form triplets (1

complete microtubule, 2 partial microtubules)

These triplets then arrange into a cylinder

200 nm in diameter, 500 nm long

Two of these line up perpendicular to form centriole

Not sure of its function yet Some believe it might be MTOCs

for spindles during cell division

Cilia/ Flagella

Long structures projecting out of a cell membrane

A core of microtubules sheathed by the plasma

Flagellum – longer and for movement of cellCilia – shorter – usually to beat up things

Plant Cells

Cell WallCellulose fiber embedded

in other polysaccharides/ proteins

Pectin and cellulose fiber (strong)

PermeableSpace between cells

above the wall: middle lamella

Things like wood may have secondary cell wall

Cell Wall

The osmotic pressure vs. the pressure from cell wall gives the plant its structure

Structure of Cellulose – resistant to degradation and enzymes – only cellulase – Protects the cell

Prevent bursting

Cell Wall

May have multiple layers1. Primary Cell Wall – thin and flexible2. Middle lamella – a thin layer between

primary walls and adjacent cells3. Secondary cell wall (only found in certain

cells) : between plasma membrane and primary cell wall – on the inside where it grows

Cell Wall

Tunnels between cells: PlasmodesmataProtoplast: A plant, bacterial or fungal cell

with its cell wall removed

Vacuoles Enclosed membrane

compartments – filled with water content/ enzymes/ proteins etc.

Storage for waste, harmful materials

Storage for water Hydrostatic pressure controlled Work with cell wall to maintain

turgidity The membrane around it:

Tonoplast

ChloroplastsPlant organelles specialized in conducting

photosynthesisLarger than mitochondriaDouble membraneHas its own DNAEndosymbiosis theory applied to it as well

Chloroplast

Inner/ Outer membraneStroma: The liquid inside the inner membraneGrana: Made up of stacks of thylakoidThylakoid: Has chlorophyll on the surface

Virus

Size: 20 – 750 nmWe are not sure if

virus is considered an organism

As it is unable to fully function without a host

Nevertheless, virus is a fascinating component to Biology worthy of studies

Virus Structure

Consists of an RNA molecule protected by a protective protein coat called capsid

Capsid made up of proteins called capsomere

On the outside a protein envelope gives it another layer of protection

Glycoproteins/lipids stuck out from the envelope

Plant Cell Vs. Animal Cell

Common Nucleus ERs/ Golgi body Plasma membranes Phospholipid bilayer Mitochondria Gap between cells (gap

junction/ Plasmodesmata) Both have cytoskeleton Peroxisomes

Differences Cell Wall Cell membrane: Glycolipid/

Glycoprotein Centrioles Central vacuoles Chloroplasts