Intracellular Processes

Question 1

what are 2 strategies that segregate molecules in cells

Answer 1

multicomponent complexes and compartmentalisation into membrane-bound organelles

Question 2

what is the sedimentation rate

Answer 2

how quickly something settles at the bottom after centrifugation

Question 3

how many Svedberg is a ribosome

Answer 3

60S + 40S = 80S (since its non-linear)

Question 4

what is one of the main targets of antibiotics

Answer 4

ribosomes of bacterial cells are they are a different size to human ribosomes.

Question 5

what do common clinically used antibiotics target

Answer 5

either small ribosomal subunit (30S) of bacteria e.g. doxycycline, streptomycin (which prevents tRNA binding or moving through ribosome) or peptidyl-transferase centre on the large subunit (50S) e.g. erythromycin (prevents polypeptide chain from elongating)

Question 6

what are the 2 pathways of proteins after being synthesised

Answer 6

ribosome > ER > Golgi > plasma membrane or lysosome. “secretion”

ribosome > cytosol > nucleus, mitochondria or peroxisomes. “stays put”

Question 7

where are signal peptides found

Answer 7

they are specific sequences found on N-terminal amino acids

Question 8

how are proteins guided to the ER surface

Answer 8

the signal peptide/sequence is guided to the ER membrane by signal-recognition particle (SRP). SRP is in the cytosol and binds to the ER signal peptide when its exposed on the ribosome. the SRP receptor is embedded on the ER membrane

Question 9

where are proteins threaded through when they’re being synthesised

Answer 9

the protein channel ‘translocon’ in the ER membrane

Question 10

what happens to the signal peptide when the protein has been through the translocon

Answer 10

the signal peptide is cleaved by signal peptidase (an ER enzyme)

Question 11

protein in the ER lumen is encapsulated into a ____ ____ that is secreted from the ER

Answer 11

transport vesicle

Question 12

what is the cis cisterna

Answer 12

a group of fused vesicles containing translated proteins made by the ribosome

Question 13

proteins are sorted in what part of the golgi

Answer 13

the trans Golgi network

Question 14

the trans Golgi network buds off into ___

Answer 14

vesicles

Question 15

what is the signal that indicates a protein has to be exocytosed

Answer 15

‘stop translocation’ at C terminus

Question 16

how are proteins directed to being endocytosed

Answer 16

directed to the lysosome > a specific sugar chain is added in the Golgi apparatus (mannose-6-phosphate). Proteins labelled with M6P bind to a specific receptor in Golgi membrane. initially, the protein will be targeted to an endosome which matures to become a lysosome.

Question 17

the __ is an organelle that contains molecules to be ___

Answer 17

endosome, degraded

Question 18

only proteins destined for the ___ have the M6P signal

Answer 18

endosome

Question 19

proteins that are extensively glycosylated are called ____, proteins with a small sugar component are called ____

Answer 19

proteoglycans, glycoproteins

Question 20

what do the following words mean the addition of and what effect does this have on function

Answer 20

phosphorylation > addition of a phosphate group > alters activity of protein.
acetylation > addition of an acetyl group > in histones (regulation of gene expression).
farnesylation > addition of a farnesyl group > targets proteins to cytoplasmic face of plasma membrane.
ubiquitination > addition of a ubiquitin chain > targets protein for degradation

Question 21

what will target a protein to the plasma membrane

Answer 21

a ‘stop translocation’ peptide at the C terminal

Question 22

what will target a protein to the lysosome

Answer 22

M6P sugar side chains

Question 23

what will target a protein to the nucleus

Answer 23

nuclear localisation signal in protein sequence. (importin is analogous to SRP and nuclear pore is analogous to ER pore)

Question 24

what will target a protein to the mitochondria

Answer 24

mitochondrial import sequence, kept unfolded by binding to ATP-dependent chaperone proteins. Imported via translocases (TIM and TOM)

Question 25

what will target a protein to peroxisomes

Answer 25

C terminal tripeptide

Question 26

what are the 2 pathways of protein degradation

Answer 26

lysosomal degradation and proteasomal degradation

Question 27

what are characteristics of proteins that undergo lysosomal degradation

Answer 27

long half-life, often membrane or extracellular proteins from pathogens

Question 28

what are characteristics of proteins that undergo proteosomal degradation

Answer 28

short half-life, key metabolic enzymes, defective proteins

Question 29

lysosomal degradation is carried out by lysosomal enzymes such as

Answer 29

hydrolase, lipases, nucleases, proteases/proteolytic enzymes. these enzymes are activated by the acidic environment inside the lysosome.

Question 30

lysosomal degradation is used for proteins with a long half life. this process is known as ___

Answer 30

autophagy. cell looking after itself

Question 31

name 3 kinds of proteins lysosomal degradation is used for and how they are brought into the cell

Answer 31

membrane proteins brought into the cell via endocytosis. extracellular proteins brought into the cell via receptor-mediated endocytosis. pathogenic proteins brought into the cell via phagocytosis

Question 32

what are proteasomes

Answer 32

cylindrical protein complexes in the cytosol

Question 33

the walls of the proteasome are formed of ____ ___

Answer 33

protease enzymes

Question 34

the active sits of the proteasome is ___ ___

Answer 34

inside cylinder

Question 35

what have to be moved to allow the proteasome to degrade proteins? what type of process is this

Answer 35

the protein stoppers at either end. this is an atp-dependent process

Question 36

proteosomal degradation is used to remove proteins with a short half life, such as ___

Answer 36

seconds or minutes

Question 37

proteins that are degraded by the proteasome have a specific sequence. what is this

Answer 37

PEST sequence. rich in proline, glutamic acid, serine and threonine

Question 38

____ proteins take ____ protein to the proteasome

Answer 38

shuttling, ubiquitinated

Question 39

ubiquitinated proteins are ___, ___ and ___

Answer 39

recognised, unfolded and translocated. they are degraded into the proteasome to give peptides

Question 40

peptides from the proteasome are digested by ___ ____

Answer 40

cytosolic peptidases

Question 41

summarise differences between lysosomal and proteosomal degradation.

Answer 41

lysosomal > endocytosis, phagocytosis or receptor-mediated.

proteosomal > ubiquitin-mediated