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Biochemistry > Exam 4: Protein Translation & post-translation > Flashcards

Exam 4: Protein Translation & post-translation Flashcards

1
Q

5’ UTR

A

untranslated region at 5’ end of mRNA

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2
Q

3’ UTR

A

untranslated region at 3’ end of mRNA

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3
Q

open reading frame

A

area of mRNA translated into protein

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4
Q

monocistronic mRNA

A

mRNA contains only one open reading frame

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5
Q

polycistronic mRNA

A

mRNA contains several open reading frames

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6
Q

tRNA

A

anneal to 3-base codons on mRNA at 3-base anticodon region

have an amino-acid linked at the acceptor terminus

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7
Q

Protein synthesis occurs in

A

the cytosol, on ribosomes

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8
Q

Ribosomes

A

have two subunits, composed of 1-3 RNA molecules (rRNA) and dozens of proteins

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9
Q

Two types of ribosomes in humans

A

Cytoplasmic - synthesis of bulk of proteins

Mitochondrial - protein synthesis inside mitochondria

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10
Q

Translation initiation

A

IF2a activated by binding to GTP, binds to methionine-tRNA to form ternary complex
Terneray complex binds to a small ribosomal subunit
An mRNA molecule binds to structure to form pre-initiation complex
Pre-initiation complex binds to large ribosomal subunit to form initiation complex
eIF2a-GTP is hydrolyzed and GDP-eIF2a is released

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11
Q

eukaryotic initiation factor 2a (eIF2a)

A

activates initiation of protein translation by binding to GTP

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12
Q

Ternary complex

A

GTP-eIF2a and methionine-tRNA

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13
Q

Pre-initiation complex

A

ternary complex, small ribosomal subunit, and mRNA

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14
Q

Initiation complex

A

small & large ribosomal subunit, mRNA, tRNA-methionine

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15
Q

Elongation phase of translation starts after

A

the initiator methionine-tRNA binds to the P site of the ribosome

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16
Q

elongation factor (EF-1)

A

required to add a second tRNA to A site of ribosome

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17
Q

eukaryotic release factor (eRF)

A

pairs with stop codon

when attached GTP is hydrolyzed, peptide is released from P site and ribosome separates

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18
Q

Streptomycin

A

antibiotic - binds to small subunit and inhibits initiation, causes mistranslation of codons

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19
Q

Neomycin and gentamicin

A

antibiotic - bind to ribosomes and cause mistranslation of codons

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20
Q

Tetracycline

A

antibiotic - blocks A site of ribosomes and prevents tRNA binding

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21
Q

Chloramphenicol

A

antibiotic - prevents peptidyl bond formation in protein translation

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22
Q

Ricin toxin

A

removes adenine bases from various positions of the rRNA in large subunit, prevents translation

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23
Q

Diphtheria toxin

A

inactivates EF-2 by ADP-ribosylation, prevents translation

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24
Q

EF-2 (elongation factor)

A

provides energy for movement of mRNA one codon further, opening A site of ribosome

25
Q

Methods for regulating translation

A
  1. Preventing the recognition of a start codon - binding protein to 5’ UTR of mRNA prevents recognition of start codon
  2. Regulating activity of initiation factors - phosphorylation of eIF-2 in response to certain stimuli inactivates initiation factor and turns off translation
26
Q

Heat shock proteins (HSPs)

A

chaperone proteins that repair proteins damaged by heat and other stresses - help proteins fold correctly

27
Q

Proteins destined for export from the cell are synthesized in the

A

endoplasmic reticulum
signal sequence peptide emerges from ribosome & recognized by SRP, moving the ribosome complex to the ER - binds to docking protein that transfers ribosome to transmembrane channel - translocon
As translation continues, peptide is threaded into ER

28
Q

signal recognition particle (SRP)

A

recognizes signal sequence that peptide is being transported out of cell and binds to docking protein - transferring ribosome to translocon

29
Q

translocon

A

transmembrane channel that threads newly synthesized proteins from ribosome into ER

30
Q

Unfolded protein response

A

triggered by accumulation of unfolded proteins in ER - such as during starvation and cholesterol overload
Inhibition of global protein translation
Induce chaperone production - improve chances of proper folding
Considers apoptosis - if unfolded protein amount exceeds capacity for repair

31
Q

Glycosylation is important because

A
  1. it changes the physical properties of the protein
  2. carbohydrates on protein surface are recognition sites for trafficking, protein interactions, recognition, and immune response
32
Q

Glycosyltransferases

A

transfer sugar from an activated sugar nucleotide to an acceptor substrate
Specific for sugar donor, acceptor molecule, and type of bond formed

33
Q

N-linked Glycosylation

A

Starts in ER before folding done, continues as protein goes through Golgi apparatus
oligosaccharide molecule is added to amino group of an asparagine residue

34
Q

Modifications in Golgi yield what two types of N-glycosylated proteins?

A 
High mannose type
Complex type (mannose and 5 other charbohydrates)
35
Q

O-linked Glycosylation

A

occurs only on fully folded proteins after it has reaced the Golgi aparatus
transfer N-acetyl-galactosamine to hydroxyl group of serine or threonine resideues on surface of protein

36
Q

O-linked glycosylation is important in

A

blood types - attaches blood group antigens on red blood cells
H-antigen discriminates between self and foreign particles in blood - has 2 alleles, A & B

37
Q

A allele

A

adds N-acetylgalactosamine to H antigen

38
Q

B allele

A

adds galactose to H antigen

39
Q

O allele

A

non-functional and adds nothing to H antigen

40
Q

A & B alleles

A

express both forms of H antigen on surface of blood cells

41
Q

Failure to hydroxylate proline

A

collagen disorders - Scurvy, Ehlers-Danlos syndrome, etc

42
Q

failure to convert cysteine to formylglycine causes

A

multiple sulfatase deficiency (MSD) - sulfated glycosaminoglycans accumulate in lysosome

43
Q

Timming at N-terminus of protein

A

proteolysis removes N-terminal amino acids & modifies new terminus - many proteins need a different start than methionine

44
Q

Addition of hydrophobic moieties to protein

A

link membrane proteins to long-chain, hydrophobic molecules to change their surface properties

45
Q

C-terminus additions

A

glycosylphosphatidyl-inositol (GPI) anchor to C-terminus to tether to external side of plasma membrane

46
Q

Targeting of proteins to lysosome by

A

phosphorylating mannose residues of high-mannose glycoproteins
Mannose-6-P on protein surface targets vesicles to lysosome

47
Q

Key features of proteins targeted for mitochondria

A

Unfolded - stabilized by chaperones
Synthesized with large N-terminal presequence - interacts with receptor in outer mitochondrial membrane (cleaved off by matrix proteases in mitochondria)

48
Q

TOMs & TIMs

A

translocases of outer and inner mitochondrial membrane - channel through which preprotein enters mitochondrial matrix

49
Q

Deafness-dystonia syndrome

A

mitochondrial disorder caused by mutation in a TIM component - impairs cellular energy production by preventing assembly of fully functional mitochondria

50
Q

Cystic fibrosis

A

caused by deletion of one codon from CFTR1 gene
Interferes with folding and glycosylation of protein
CFTR protein is moved into cytosol and degraded instead of being sent to plasma membrane

51
Q

I-cell disease

A

transfer of phosphate to mannose is impaired
lysosomal proteins do not reach their compartment & function is compromised - leads to accumulation of undegraded proteins in lysosomes
In fibroblast - dense bodies of nonfunctional lysosomes & content
In serum - lysosomal proteins that did not reach lysosomes

52
Q

Mechanisms for protein degradation in cell

A

Lysosome & proteasome

53
Q

Lysosome

A

nonspecific degradation of extracellular and intracellular proteins
can digest itself - autophagy
contains high concentrations of diverse hydrolytic enzymes

54
Q

Proteasomes

A

required for specific degradation of cytoplasmic proteins

55
Q

Ubiquitin

A

mark protein for proteasomal destruction - needs multiple units of ubiquitin on same protein (poly-ubiquination) to signal for destruction
Activated by E1 enzymes, conjucated to E2 enzymes, and ligated to targets by E3 proteins
Recycled - not degraded by proteasome with protein

56
Q

Enzyme E3

A

identifies proteins for ubiquination & transfers ubiquitin to protein
Specific isozymes for certain classes of substrates

57
Q

Protein lifespan determined by:

A

Conformation (correct folding, no hydrophobic domains on surface of protein)
N-terminal residue (arginines or lysines are less stable than proteins with methionine or serine at N-terminal)
Other sequence elements (PEST sequences shorten lifespan of protein)

58
Q

PEST sequences

A

proline-glutamine-serine-threonine sequence in protein

Shorten life of protein

Biochemistry (15 decks)

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