L3 - Cell Organelles

Question 1

Nucleus:

Answer 1

Diameter: a few um
Surrounded by double membrane - nuclear envelope. Nuclear envelope has pores so controls proteins in and out of cell.
This encloses the nucleoplasm.
Contains DNA which is packaged with proteins as chromosomes.
Site of RNA synthesis (transcription).

Question 2

ER:

Answer 2

Network of interconnecting closed membrane vesicles.

RER:
Has ribosome
Protein synthesis and secretion
When protein made, it’s moved into lumen and secreted in vesicle.

SER: 
Lacks ribosomes
Can have 3 functions: 
1. Steroid hormone synthesis
2. Detoxify organic compounds in liver
3. Release of glucose from glycogen in liver.

Question 3

Golgi complex:

Answer 3

Stack of flattened membrane vesicles.
Modify protein by adding sugar.
Transport proteins to be exocytosised to membrane or to organelles (lysosomes).

Question 4

Lysosomes:

Answer 4

Degrade faulty/unwanted proteins or damaged organelles.
Use degradation enzymes where opt pH is low (around 5). Cytosol pH7 so H+ move into lysosome through hydrogen pump.
If leaked out it could have been dangerous as damage cell and break unwanted things down.
But high pH so enzyme denature.

Question 5

Peroxisomes:

Answer 5

Degrade FA and toxic compounds.
Oxidise organic compounds can releases H2O2.

Breaks 2H2O2 down to 2H2O and O2.
USES CATALASE.

Question 6

Mitochondria:

Answer 6

Oval shaped.
1μm x 2μm
Same size as bacteria
Main site for ATP production by oxidative phosphorylation.
Takes up to 25% of cytoplasm.
OMM 50:50 IMM 20:80 require more protein than lipid for ATP synthesis.
IMM forms cristae which protrudes in matrix. Increases SA.

Mitochondria derived from bacteria as own DNA RNA and ribosomes. Makes own proteins. And reproduce by dividing.

Question 7

Cytosol:

Answer 7

Has cytoskeleton. Network of protein fibres. Maintains shape of cell and move organelles and vesicles.

Has inclusion bodies e.g. Glycogen granules.

Has metabolic enzymes. 20-30% protein.

Question 8

Sub cellular fraction:

Preparing cell:

Differential-velocity centrifugation:

Equilibrium-density centrifugation:

Answer 8

Sub cellular fractionation:
Separation of different organelles in large numbers.

Preparing cells:
Cells must be physically disrupted. Held in similar solution of pH salt content and tonicity.
Kept cold.

Differential-velocity:
Centrifuge at successively increased speeds and produce different sub cellular fractions.

Equilibrium-density:
Purify different fractions to get specific organelles. Separate by density. Can look at individual organelles and test for each one.
E.g. Catalase for peroxisomes
E.g. Cytochrome c for mitochondria.

Shows increasing density of sucrose. Bottom is more dense so more conc of sucrose.

Question 9

What types of behaviour affect cell in centrifuge tube?

Answer 9

Volume, Density (Mass/Volume) and Shape