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

Exam 4: Protein Translation & post-translation Flashcards

(58 cards)

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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)

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A

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

25
Methods for regulating translation
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
Heat shock proteins (HSPs)
chaperone proteins that repair proteins damaged by heat and other stresses - help proteins fold correctly
27
Proteins destined for export from the cell are synthesized in the
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
signal recognition particle (SRP)
recognizes signal sequence that peptide is being transported out of cell and binds to docking protein - transferring ribosome to translocon
29
translocon
transmembrane channel that threads newly synthesized proteins from ribosome into ER
30
Unfolded protein response
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
Glycosylation is important because
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
Glycosyltransferases
transfer sugar from an activated sugar nucleotide to an acceptor substrate Specific for sugar donor, acceptor molecule, and type of bond formed
33
N-linked Glycosylation
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
Modifications in Golgi yield what two types of N-glycosylated proteins?
``` High mannose type Complex type (mannose and 5 other charbohydrates) ```
35
O-linked Glycosylation
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
O-linked glycosylation is important in
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
A allele
adds N-acetylgalactosamine to H antigen
38
B allele
adds galactose to H antigen
39
O allele
non-functional and adds nothing to H antigen
40
A & B alleles
express both forms of H antigen on surface of blood cells
41
Failure to hydroxylate proline
collagen disorders - Scurvy, Ehlers-Danlos syndrome, etc
42
failure to convert cysteine to formylglycine causes
multiple sulfatase deficiency (MSD) - sulfated glycosaminoglycans accumulate in lysosome
43
Timming at N-terminus of protein
proteolysis removes N-terminal amino acids & modifies new terminus - many proteins need a different start than methionine
44
Addition of hydrophobic moieties to protein
link membrane proteins to long-chain, hydrophobic molecules to change their surface properties
45
C-terminus additions
glycosylphosphatidyl-inositol (GPI) anchor to C-terminus to tether to external side of plasma membrane
46
Targeting of proteins to lysosome by
phosphorylating mannose residues of high-mannose glycoproteins Mannose-6-P on protein surface targets vesicles to lysosome
47
Key features of proteins targeted for mitochondria
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
TOMs & TIMs
translocases of outer and inner mitochondrial membrane - channel through which preprotein enters mitochondrial matrix
49
Deafness-dystonia syndrome
mitochondrial disorder caused by mutation in a TIM component - impairs cellular energy production by preventing assembly of fully functional mitochondria
50
Cystic fibrosis
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
I-cell disease
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
Mechanisms for protein degradation in cell
Lysosome & proteasome
53
Lysosome
nonspecific degradation of extracellular and intracellular proteins can digest itself - autophagy contains high concentrations of diverse hydrolytic enzymes
54
Proteasomes
required for specific degradation of cytoplasmic proteins
55
Ubiquitin
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
Enzyme E3
identifies proteins for ubiquination & transfers ubiquitin to protein Specific isozymes for certain classes of substrates
57
Protein lifespan determined by:
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
PEST sequences
proline-glutamine-serine-threonine sequence in protein | Shorten life of protein

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