Cell ultrastructure 2.1.1.

define prokaryotes

cell with no membrane bound nucleus or organelles

bacteria- prokaryotic or eukaryotic

example of a prokaryotic cell

organelles in a bacteria cell (8)

cell surface membrane, mesomome, peptidoglycan cell wall, capsule, (naked) circular DNA, ribosomes, bacterial flagellum, plasmid

bacterial ribosomes

70S, free in cytoplasm, not membrane bound

bacterial mesomome

increases surface area for aerobic respiration

bacterial capsule

slimy layer outside cell wall, allows adhesion

define eukaryotes

cells with nucleus and membrane bound organelles, can be unicellular or multicellular

kingdoms made up of eukaryotic cells

animal, plant, fungi, protoctista

advantages of compartmentalisation

so enzymes and substrates stay in specific space, increases efficiency of reactions, increases likelihood of collisions, provides optimal conditions (e.g. pH) for specific reactions

organelles in animal cells (14)

nucleus, nucleolus, chromatin, nuclear envelope, nuclear pores, smooth endoplasmic reticulum, rough endoplasmic reticulum, centriole, ribosomes, golgi apparatus, lysosome, mitochondrion, plasma membrane, cytoplasm/cytosol

organelles in plant cells not in animal cells (3)

cellulose cell wall, chloroplasts, permanent vacuole

cytosol

cytoplasm= cytosol+all organelles (except nucleus), jelly-like liquid, contains cytoskeleton, site of many chemical reactions, surrounded by cell surface membrane

features and roles of the cell surface membrane

a.k.a plasma membrane, partially permeable, boundary between cell and its environment, site for chemical reactions and cell-cell signalling, dynamic structure e.g. phagocytosis, surface area can be increased by villi and microvilli

nucleus components (4)

nuclear envelope, nuclear pores, nucleolus, chromatin

nuclear envelope

double membrane, encloses DNA, protects it from cytoplasmic enzymes

nuclear pores

gaps in nuclear envelope, entry point for: regulatory proteins, nucleotides, steroid hormones, exit point for mRNA (DNA cannot leave nucleus)

nucleolus

site of ribosomes production

what is chromatin

DNA associates with histones (proteins)- {heterochromatin and euchromatin}

what happens to DNA before cell divides

DNA condenses into chromosomes, rest of the time appears as ‘grainy chromatin’

what are ribosomes and what is their role

site of protein synthesis, very large macromolecule made up of protein and ribosomal RNA, can be free in cytoplasm or on surface of RER, not membrane bound

ribosome sizes

80S in eukaryotes (large), 70S in prokaryotes (small)

endoplasmic reticulum

network of flattened sacs-cisternae- originating from outer membrane of nucleus/continuous with nuclear envelope, interior of cisternae called lumen, membranes of cisternae bud off into vesicles

vesicle

a small sac formed by a membrane (containing chemical from the lumen of the reticulum)

Rough endoplasmic reticulum

site of protein synthesis (on the ribosomes), and protein transport, ribosomes on surface (rough), newly formed polypeptides from ribosomes enter lumen of RER and are packaged into transport vesicles to go to the Golgi

what is the role of the smooth endoplasmic reticulum

site of lipid and carbohydrate synthesis, no ribosomes on it

roles of the golgi apparatus

sit of protein+ lipid modification and secretion, enter via vesicles

modification in the Golgi

• -happens inside the lumen

• -include: addition of a carbohydrate chain to proteins to make glycoproteins, and to lipids to make glycolipids

• prosthetic groups of proteins added e.g. haemoglobin

• final products are pinched off the end of the cisternae inside a secretory vesicle

secretion in the Golgi

vesicles transport products to their destination, inside or outside of cells

what are lysosomes

a vesicle with a specific function, formed by Golgi, remain in cell, contain hydrolytic (destructive) enzyme- lysozyme, degrades unwanted substances in the cell

what are extracellular proteins

proteins made in the cell and secreted in order to carry out their functions outside the cell

examples of extracellular proteins

digestive enzymes, hormones, antibodies

features and function of mitochondria

site for aerobic respiration, double membrane, has it’s own ribosomes and DNA, there are mitochondria in metabolically active cells (e.g. white blood cells, liver cells, neurones)

mitochondria structure diagram

aerobic respiration stages

glycolysis, link reaction and Krebs cycle, oxidative phosphorylation

where does glycolysis in aerobic respiration occur

1st stage. occurs in cytoplasm outside mitochondria

where does the link reaction and Krebs cycle in aerobic respiration occur

2nd stage, occurs in the matrix of mitochondria

aerobic respiration oxidative phosphorylation

3rd stage: electron transport chain and chemiosmosis, occurs on the inner mitochondrial membrane

evolution of mitochondria

aerobic bacteria:

• same size ribosomes (70S)

• same size ring of circular DNA

• double membrane

  • size and shape of organelle

what is the cytoskeleton

filamentous structures which allow:

1. mechanical strength, support, stability and shape

2. transport within cells

3. movement of cells

made up of microfilaments, microtubules, intermediate filaments

intermediate filaments function

• mechanical strength: help cell resist compression forces

• support and stability for cell shape: holding organelles in place e.g. anchorage of nucleus

are a fixed length for stability so are not involved in cell movement

microtubules structure

cylindrical, polymerised, globular tubulin proteins, scaffolding like tracks

microfilaments structure

contractile actin fibres, change length with addition/ removal of subunits, contraction and polymerisation lead to change in length of filaments, subunits

microfilaments subunits

added at different rates to each end of fibres, not symmetrical, must be correct orientation to be added, at minus end must change shape before being added, not at plus end, added at a faster rate at plus end, filament increases in length faster in one direction, subunits added/removed controlled by concentration of subunits in cytoplasm at either end, at certain conditions subunits added at one end and removed at other, increasing length at one end at edge of cell causes cell to move in that direction

microtubules functions overview

mechanical strength

transport within cells:

a) during protein synthesis

b) during mitosis

cell movement

microtubules mechanical strength

help cell resist compression forces

microtubules transport within cell a) during protein synthesis

• transport of mRNA from nucleus to ribosomes

• transport of polypeptide within lumen of RER

• movement of transport vesicles from RER to golgi apparatus

• movement of vesicles between cisternae of golgi

• movement of secretory vesicles from golgi to plasma membrane

microtubules transport within cells b) during mitosis

• centrioles to allow attachment points for the spindle fibres at the poles

  • spindle fibres to allow movement of chromosomes to opposite poles

microtubules cell movement

• flagellum to propel the cell forward e.g. sperm

• cilia which produce wafting motion to move substances outside the cell e.g. mucus

centrioles

formed by microtubules, involved in cell division, anchor point for spindle fibres

spindle fibres

formed by microtubules, form a centrosome with centrioles

flagella and cilia

formed by microtubules enclosed by a membrane, 9-2 structure, eukaryotic flagellum different to prokaryotic

microfilaments function

cell movement:

• cytokinesis to divide the cell into two after mitosis

• movement of plasma membrane e.g. phagocytosis, exocytosis

function of chloroplasts

site of photosynthesis

chloroplast structure

evolution of chloroplast

aerobic bacteria:

• double membrane

• 70S ribosome

• circular DNA

1st stage of photosynthesis

light dependent reactions: light energy → chemical energy

2nd stage of photosynthesis

light independent reactions: CO2 is fixed into sugar

membrane of the large permanent central vacuole

tonoplast

roles of the large permanent central vacuole

storage, maintaining turgor pressure

storage role of vacuole

contains:

• waste (later removed by leaf fall)

• pigments- anthocyanins (to attract pollinators and animals for seed dispersal)

• cell sap: fluid containing sugars, amino acids, salts

maintaining turgor pressure role of vacuole

1. water enters vacuole

2. pressure against cell wall

3. turgor (pressure) creates

4. turgid cells support the plant

what is the cellulose cell wall made of and where makes it?

cellulose fibres: formed in SER, secreted by Golgi apparatus by secretory vesicles

where cell walls of adjacent cells meet?

middle lamella

functions of cellulose cell wall

• mechanical support and strength (increased by presence of lignin in wood)

• osmotic support

osmotic support in cellulose cell wall

cellulose has high tensile strength, when water enters the cell, the cell wall resists expansion, prevents cell from bursting and internal pressure created (turgor pressure), cell becomes turgid, plant tissue supported

cellulose cell wall permeability?

highly permeable to water, allows easy passage of water through the roots and leaves

components of cellulose cell wall

lignin (wood), cutin (waxy cuticle), suberin (roots)- all make cell wall less permeable to water

how cellulose cell wall determines shape of leaf?

orientation of cellulose fibres determine the shape of the plant cell and therefore the shape of the leaf

what is the fungi cell wall made of

made of chitin

plasmodesmata

small gaps in cell wall and middle lamella where the cytoplasm of adjacent cell meet

what is cell fractionation

a method used to isolate/ separate organelles

cell fractionation method

1. done in ice-cold solution that has same solute concentration as the inside of the cells

2. homogenate is spun at increasingly high speeds in a centrifuge- called cell fractionation

define homogenisation

cellular organelles being isolated by breaking up the cells

how cell fractionation works

cell fragments, including organelles, move down the centrifuge tube depending on their mass and the speed of the centrifuge. heavier organelles need a lower centrifugal speed to compact the organelles into a pellet