1.7 - Sub-cellular organelles – Bioch + OB

Question 1

structure + function of the cell membrane

Answer 1

see other topic

Question 1

size of the cell membrane

Answer 1

5-7nm

Question 2

structure of the rER

Answer 2

Dotted with ribosomes – dotted appearance

membrane is continuous with the outer membrane of the nuclear envelope = facilitating efficient transport of mRNA from the nucleus to ribosomes for translation.

Question 3

function of the rER

Answer 3

Site of protein synthesis – matured mRNA fragments being shipped into this region through nuclear envelopes

Used as a template for translation

N-linked glycosylation also takes place here in glycoprotein formation

Question 4

structure of the sER

Answer 4

Found more freely in cytoplasm + lacks ribosomes

Question 5

function of the sER

Answer 5

Responsible for synthesis of lipids / phospholipids / sterols – typically following lipid processing or lipogenesis

ER plays a crucial role in detoxifying drugs and harmful metabolites

storage site for calcium

Well-developed sER = muscular sarcoplasmic reticulum, from which Ca2+ levels are regulated in response to signals at the NMJ

Question 6

structure of ribsomes

Answer 6

Small proteins combined with rRNAs

80s in eukaryotes

Question 7

function of ribosomes

Answer 7

Site of translation of mRNA to a primary sequence = uses tRNA to align appropriate amino acids + condense them to form peptide bonds

Question 8

structure of golgi apparatus

Answer 8

Does not touch
Found in cytosol
cis + trans face

Question 9

function of the golgi apparatus

Answer 9

primary role = package extracellular proteins in vesicles as they move from the cis to trans face = allows for more effective movement to the plasmalemma for endocytosis + secretion

protein modification - glycosylation + phosphorylation= provides post-translational modifications

produces lysosomes

Question 10

structure of mitochondria

Answer 10

Double Membrane:
Outer Membrane
Inner Membrane - Highly folded into cristae, which increase surface area for biochemical reactions; impermeable to ions and small molecules.

Intermembrane Space: The space between the outer and inner membranes, involved in creating a proton gradient.

Matrix: The innermost compartment containing enzymes for the citric acid cycle, mitochondrial DNA, ribosomes, and metabolic substrates.

Question 11

function of mitochondria

Answer 11

ATP production
anabolic functions
amino acid metabolism
ca2+ homeostasis with ER
lipid synthesis

Question 12

significance of exposure to the internal membrane of mitochondria

Answer 12

exposure to internal membrane can promote the rest of the cell to initiate the caspase-9 mediated cell apoptosis pathway

Question 13

why dont all cells have mitochondria

Answer 13

not all cells have these organelles as they require an oxygen-rich environment for normal function – RBCs

Question 14

structure of lysosomes

Answer 14

enclosed by single lipid bilayer

contain a variety of digestive enzymes (hydrolases) = proteases, lipases, nucleases, carbohydrases. = function optimally at acidic pH 4.5-5

maintained that pumps in the membrane that transport H⁺ ions into the organelle

Question 15

function of lysosomes

Answer 15

break down damaged proteins / organelles / pathogens within cell

endocytosis
phagocytosis
autophagy
apoptosis

reply on strong cell membrane and closely controlled H+ transportation = to flood lumen of the organelle with protons + hydrolytic enzymes of lysozyme family = then breaks down anything caught inside it

Question 16

what is autophagy

Answer 16

degrade damaged organelles and recycle their components

Question 17

structure of endosome

Answer 17

specific vesicles produced by the Golgi apparatus

Question 18

function of endosome

Answer 18

sorting of endocytosed material -Some materials (like receptors) are recycled back to the plasma membrane, while others (like ligands) are sent to late endosomes for eventual degradation in lysosomes

shuttle molecules between the plasma membrane, lysosomes, and the trans-Golgi network

Question 19

structure of peroxisome

Answer 19

single membrane

matrix = contains a variety of oxidative enzymes, such as catalase, urate oxidase, and D-amino acid oxidase.

in cytoplasm

Question 20

function of peroxisome

Answer 20

Proteins destined for peroxisomes are synthesised in the cytosol + contain a specific sequence known as a peroxisomal targeting signal

involved in the β-oxidation of very long-chain fatty acids (VLCFAs)

fatty acids are shortened in the peroxisome + then further processed in mitochondria to produce energy (ATP).

peroxisomal β-oxidation does not directly contribute to ATP production = but generates hydrogen peroxide as a byproduct

breaking down hydrogen peroxide = harmful byproduct of oxidative reaction = into water and oxygen using the enzyme catalase.

neutralise ROS

Question 21

three major parts of the cytoskeleton

Answer 21

microtubules

intermediate fibres

actin

Question 22

structure of microtubules

Answer 22

polymers of the protein tubulin

consist of alpha and beta tubulin = forms heterodimers

heterodimers polymerise into protofilaments

one microtubule is made from 13 protofilaments

slightly staggered

Question 23

how many protofilaments make one microtubule

Answer 23

13

Question 24

why are microtubules slightly staggered

Answer 24

because of the two types of contact - vertical and lateral contact

two protofilaments not completely parallel in lateral contact= shifted along z axis

important in the dynamic microtubule lattice

Question 25

whats the difference between alpha and beta tubulin

Answer 25

both bind to GTP

beta tubulin can hydrolyse GTP to GDP alpha can not

Question 26

what happens when beta tubulin hydrolyses GTP into GDP

Answer 26

changes its conformation from T form to D form

now D form doesnt really fit staggered conformation

so leads to the depolymerisation of protofilaments

Question 27

what is dynamic instability

Answer 27

GTP and beta tubulin is loaded onto the growing plus ends of microtubules = GTP cap

as long as hydrolysis not outpace the assembly rate (addition of more GTP loaded subunits) = microtubules grow

if hydrolysis rate greater then assembly = catastrophe

if rate of assembly greater = recovery

Question 28

plus and minus end of microtubules

Answer 28

Plus end = rapidly built and destabilised

Minus end = near the nucleus, stabilised

Question 29

define catastrophe and recovery

Answer 29

Question 30

importance of dynamic instability

Answer 30

depolymerisation can be used to create force - e.g. chromosomes attached to microtubules are removed by catastrophic depolymerisation

Question 31

What are MAPs, and how do they regulate microtubule dynamics?

Answer 31

Microtubule-Associated proteins

interact with microtubules

• promote microtubule polymerisation and prevent excess depolymerisation
• modulate the rate of microtubule growth and shrinkage by binding to tubulin subunits or the MT lattice
• help organise MT into bundles + networks

Question 31

example of MAPs

Answer 31

Tau:
Found in neurons, Tau stabilizes microtubules in axons.

Pathological aggregation of Tau is linked to neurodegenerative diseases like Alzheimer’s.

Question 32

what is gamma tubulin

Answer 32

nucleates microtubules at microtubule organising center = associated with minus end

Question 33

polarity of MTs

Answer 33

cell specific

important for the directionality of transport - moving organelles around the cell