Cell Biology

Question 1

how does cholesterol control membrane fluidity?

Answer 1

packs phospholipids

Question 2

what are 3 functions of proteins in the phospholipid bilayer?

Answer 2

• transport of hydrophilic molecules
• cell-cell communication
• communication via endocrine / cytokine etc. systems

Question 3

what are 3 categories of protein transporters?

Answer 3

• passive
• active
• secondary active pumps

Question 4

what is the difference between endocytosis, phagocytosis and pinocytosis?

Answer 4

• endocytosis - general intake
• phagocytosis - done by phagocytes
• pinocytosis - bulk intake of fluids

Question 5

what allows the surface membrane to form internal vesicles?

Answer 5

clathrin molecules allow bilayer to bend inwards, forming a clathrin-coated vesicle

Question 6

what is cytosol?

Answer 6

intracellular fluid

Question 7

what allows the cytoplasm to maintain its structure?

Answer 7

cytoskeleton network

Question 8

what structure makes up the ER?

Answer 8

external nuclear membrane

Question 9

how do ribosomes get to the RER? (3)

Answer 9

1 - signal peptide on N-terminal of protein
2 - SRP (signal recognition particle) attaches to signal peptide
3 - SRP receptor binds to RER

Question 10

what are 3 functions of the SER?

Answer 10

• lipid synthesis
• steroid / drug metabolism
• calcium store

Question 11

what is the cis-maturation model? (4)

Answer 11

1 - vesicles fuse to cis cisterna
2 - cis cisterna becomes part of medial cisternae
3 - eventually become part of trans cisternae
4 - joins the trans Golgi network (TGN) from which vesicles leave to particular destinations

Question 12

how are proteins directed to 1. lysosomes, 2. plasma membrane, 3. outside cell (via secretion)?

Answer 12

1 - addition of mannose-6-phosphate (glycosylation)
2 - ‘stop translocation’ peptide
3 - no modification

Question 13

what are glycosylated proteins called?

Answer 13

glycoproteins

Question 14

what are heavily glycosylated proteins called?

Answer 14

proteoglycans

Question 15

what is the effect of phosphorylation?

Answer 15

alters the activity of a protein

Question 16

give an pathological example of phosphorylation as a post-translation modification, and its significance

Answer 16

hyperphosphorylation of Tau protein - present in many neurological disorders

Question 17

what is the effect of acetylation?

Answer 17

on histones - regulate gene expression

Question 18

what are 2 common effects of farnesylation?

Answer 18

• mediates protein interactions

* targets proteins to plasma membrane

Question 19

what is the effect of ubiquitination?

Answer 19

tags a protein for degradation

Question 20

what are endosomes? (3)

Answer 20

• immature lysosomes
• contain proteins from Golgi
• fuse with phagocytotic vesicles

Question 21

why does the lysosome require an acidic environment? how is this maintained?

Answer 21

• digestive enzymes work in acidic environments (think stomach)
• proton ATP-ase pumps

Question 22

what 3 types of proteins need to de degraded?

Answer 22

• old proteins
• faulty proteins
• foreign proteins

Question 23

when is lysosomal degradation used? (4)

Answer 23

• autophagy of proteins with long half-lives (20 hrs)
• membrane proteins (endocytosis)
• extracellular proteins (receptor mediated endocytosis)
• pathogenic proteins (phagocytosis)

Question 24

what is the simple structure of a proteasome? (4)

Answer 24

• cylinder
• protease enzyme in walls
• internal active site
• open tube to allow protein to enter

Question 25

when is proteasomal degradation used? give 2 examples

Answer 25

• dangerous proteins with short half-lives (seconds or minutes) -> tagged with ubiquitin * metabolic enzymes * defective proteins

Question 26

what is the sequence of proteasomal degradation? (5)

Answer 26

1 - protein tagged with Ub 2 - shuttled to proteasome 3 - recognised, unfolded and translocated 4 - degraded in proteasome into a peptide 5 - extruded and digested by cytosolic peptidases

Question 27

why is the mitochondria membrane-bound?

Answer 27

separate powerful enzymes from other organelles

Question 28

what are 4 common functions of the mitochondria?

Answer 28

* ATP production * Kreb’s cycle * electron transport chain * oxidative phosphorylation

Question 29

how does the mitochondria contribute to apoptosis? (4)

Answer 29

1 - increase membrane permeability 2 - release cytochrome c 3 - forms apoptosome 4 - apoptosome activates caspase cascade

Question 30

what is the effect of apoptosis on the cell? (3)

Answer 30

* destroy nuclear lamins * activate DNases (degrades DNA phosphate backbone) * destroy cell adhesion proteins

Question 31

how do materials enter the nucleus?

Answer 31

via nuclear pores

Question 32

what is the nuclear lamina?

Answer 32

* supports the inner membrane | * composed of lamins (intermediate filaments)

Question 33

how is genetic material stored?

Answer 33

chromatin

Question 34

what are the 3 functions of the cytoskeleton?

Answer 34

shape, strength and movement

Question 35

what is the structure of microtubules, and why is this useful?

Answer 35

tubular - resists bending and stretching

Question 36

what is the main function of microtubules?

Answer 36

act as the ‘highway’ of the cell - transport organelles and vesicles

Question 37

what is the MTOC and what are its 2 functions?

Answer 37

• microtubule organising centre * microtubules attach to this * forms mitosis spindle

Question 38

where are intermediate filaments centred?

Answer 38

around nucleus - extend to periphery

Question 39

what important structures use intermediate filaments?

Answer 39

desmosomes and hemidesmosomes

Question 40

what quality of intermediate filaments helps its function?

Answer 40

maintains structural integrity - hence presence in epithelial cells

Question 41

what material makes up microfilaments?

Answer 41

actin formed into a polymer

Question 42

what are the 2 functions of microfilaments?

Answer 42

* controls cell shape | * involved in cell movement

Question 43

what cell structures are made of microfilaments?

Answer 43

* microvilli * lamellipodia (motor pulling cell forward) * filopodia (extend beyond lamellipodia)

Question 44

what is the structure of a tight junction? (4)

Answer 44

* fusion of integral proteins * between lateral membranes * in epithelial cells * held in place by actin fibres

Question 45

what are 2 functions of tight junctions?

Answer 45

* do not allow diffusion between cells | * forms a barrier between polar apical and basolateral membranes (maintains polarity)

Question 46

what are gap junctions made of?

Answer 46

connexins

Question 47

what is the purpose of gap junctions?

Answer 47

permit passage of small molecules between adjacent cells

Question 48

what is meant by the gate-fence model for gap junctions?

Answer 48

gate - regulates permeability | fence: prevents mixing between apical and basolateral surfaces

Question 49

where are desmosomes found in the skin?

Answer 49

between keratinocytes in the epidermis

Question 50

where are hemidesmosomes found in the skin?

Answer 50

between stratum basale cells and basement membrane in epidermis: dermoepidermal junctions

Question 51

what condition is caused by a mutation which alters the function of respiratory chain proteins in the mitochondria?

Answer 51

Leigh syndrome (CNS)

Question 52

what type of conditions are caused by defects in oxidative phosphorylation?

Answer 52

mitochondrial cytopathies

Question 53

why do mitochondrial diseases particularly effect the brain and CNS?

Answer 53

high energy systems

Question 54

what is Tay-Sach’s disease? what does this result in?

Answer 54

* failure to degrade lipids in lysosome | * lipids accumulate in neurones and progressively damage the nervous system

Question 55

what is Kartangener’s disease? what does this result in?

Answer 55

* mutations to dynein (responsible for movement) in cilia and flagella * frequent lung infections and male infertility

Question 56

what do defects in hemidesmosomes or intermediate filaments result in? (2)

Answer 56

* disruption of dermo-epidermal junction | * leads to blistering: epidermolysis bullosa simplex (butterfly skin)

Question 57

what can mutations in connexins result in? (2)

Answer 57

* defective GAP junctions | * associated with inherited deafness