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Molecular Cell Biology Jessica > Chapter 9 > Flashcards

Chapter 9 Flashcards

1
Q

translation is???????? (1-5)

A
  1. is the synthesis of proteins as directed by mRNA templates
  2. is the only first step in the formation of a functional protein
  3. polypeptides chains must fold in a appropriate conformations and often undergo various processing steps, sorting, and transport
  4. gene expression is regulated at the level of translation in both prokaryotic and eukaryotic cells
  5. there are also multiple controls on the amounts and activities of intracellular proteins, which ultimately regulate all aspects of cell behavior
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2
Q
  1. proteins are synthesized from mRNA templates by a process that has been highly conserved throughout evolution.

all mRNAs are read in the _____________. and polypeptide chains are sythesized from the amino to the carboxy terminus

A

5’ to 3’ direction

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3
Q
  1. ________ is specified by ____________ in the mRNA
A

each amino acid is specified by three bases (a codon) in the mRNA

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4
Q
  1. translation is carried out on_________, with tRNAs serving as adaptors
A

ribosomes

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5
Q
  1. protein synthesis involves interactions between 3 types of RNA (_______,_________,________), plus other proteins
A

mRNA, tRNA, rRNA

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6
Q

______ align amino acids with corresponding _________. They are ____ nucleotide long and have characteristic cloverleaf structures resulting from base pairing between different regions

A

tRNAs

Codons on the mRNA template

they are 70-80 nucleotides long

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7
Q

structure of RNAS

  1. all tRNAs fold in compact ________ shapes, to fit onto ribosomes during translation
A

fold into L shapes

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8
Q

structure of tRNAS

  1. tRNAs have the sequence _______ at the _____ terminus, and amino acids are covalently attached to the ribosomes of the terminal adosine
A
  1. sequence of CCA at the 3’ terminus
    sequence CCA
    at terminus 3’
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9
Q

structure of tRNAs

  1. The _________ binds to the appropriate codon by complementary base pairing
A

anticodon loop

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10
Q

attachment of amino acids to specific tRNAs is mediated by enzymes called __________________

each of these 20 enzymes recognizes a single aminoale amino acid, as well as the correct tRNA to which it should attach

A

aminoacyl tRNA synthetases

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11
Q

attachment of amino acids to tRNAs

this occurs in two steps

  1. the amino acid is joined to AMP, forming __________
  2. the amino acid is transferred to ____________ of the tRNA and AMP is released
A
  1. the amino acid is joined to AMP, forming aminoacyl AMP

2. the amino acid is transferred to the 3’ CCA terminus of the tRNA and AMP is released

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12
Q

translation of mRNA

  1. the amino acid is then aligned on the mRNA template by complementary base paring
  2. most amino acids are specified by more than one codon
  3. Cells have about 40 different tRNAs for the 2- different amino acids
  4. some tRNAs can reconize more than one mRNA codon, as a result of _________ at the _____ codon position

this allows G to pair with U, and inosine (I) to pair with U,C,or A

(guanosine is modified to inosine in the anticodons of some tRNAS)

A
  1. as a resulting of NONSTANDARD BASE PARING (WOBBLE) at the 3rd CODON POSITION
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13
Q

______________ are named according to their sedimentation rates in ultracentrifugation. ______ for bacteria and __________ for eukaryotics

Cells have many ribosomes, illustrating the importance of protein synthesis. E. coli has about 20,000; growing mammalian cells can have ten million

A

ribosomes
70s for bacteria
80s for eukaryotic

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14
Q

all ribosomes have ______ subunits. Each subunit contains ____________ and characteristic proteins

the subunits of eukaryotic ribosomes are larger and have more proteins than prokaryotic ribosomes

A

TWO subunits

contains rRNA and characteristic proteins

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15
Q

ribosome can be formed in vitro by ___________ from purified ribosomal proteins and rRNAs, which provides important experimental tool

A

self assembly

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16
Q

rRNAs form characterisitic secondary structures by ____________.
Subsequent folding results in distinct 3D stuctures

A

complementary base pairing

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17
Q

unambigous evidence for rRNA catalysis came from high-resolution structural analysis of ______ ribosomal subunit, in 2000

A

50s

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18
Q

ribosomal proteins are absent from the site of the peptidyl transferase reaction showing that _____________________.

It is now thought that ribosomal proteins play a largely structural role, and the large ribosomal subunit functions as a ribozyme

this is evolutionary implications: RNAs are thorugh to have benn the first self-replicating macromolecules

A

rRNA is responsible for catalyzing peptide bond formation

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19
Q

mRNAs have noncoding ________________ at the end.

most eukaryotic mRNAs are ____________, encoding in a single protien

prokaryotic mRNAs are often _________-, encoding multiple proteins, each of which is translated from an independent start site

A

untranslated regions (UTRs)

mono-cistronic

poly-cistronic

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20
Q

in both prokaryotes and eukaryotes, translation always _________, usually encoded by ______

A

always starts with methionine

usually encoded by AUG

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21
Q

the signals that identify initiation codons are different in prokaryotic and eukaryotic cells

  1. initiation codons in bacterial mRNAs are preceded by ___________, that aligns the mRNA on the ribosomes

They can initiate translation at the 5’ end of an mRNA and at internal initiation sites of polycistronic mRNAS

  1. eukaryotic mRNAs are recognized by the _____________ at the 5’ terminus.

the ribosomes then scan downstream of this cap until they encounter the initiation codon

A
  1. SHINE-DALGARNO SEQUENCE

2. 7-METHYLGUANOSINE CAP

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22
Q

translation occurs in 3 stages: _________,________, and ______.

a specific initatior _________ and the mRNA binds to the ______________________

A

initiation, elongation, termination

a specific initator METHIONYL tRNA and the mRNA bind to the SALL RIBOSOMAL SUBUNIT

the LARGE RIBOSOMAL unit then joins, forming a functional ribosome

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23
Q

many nonribosomal protiens are also required for various stages of translation? (true/false)

A

true

24
Q

in _________________, initiation starts with a 30S ribosomal subunit bound to __________________- IF1 and IF3

then the mRNA, initator N-formylmethionyl (fMet) tRNA, and IF2 (bound to GTP) joint the complex

IF1 and IF3 are released, a 50S subunit binds to the complex and IF2 is released

A

in bacteria

initation factors

25
Q

______________- initiation is more ocmplex, and requires at least 12 proteins, designated elFs (eukaryotic initation factors)

the initiator ______________ is bound to ____________ and the _____ is brought to the complex by __________-

A

in eukaryotes

the initiator METHIONYL tRNA is BOUND TO eLF2, and the mRNA IS BROUGHT TO THE COMPLEX by eLF4E

26
Q

“Initation of translation in cells”

  • ribosome scan down the mRNA to identify ____________
  • ATP hydrolysis
  • when AUG is identified, ______ triggers the hydrolysis of GTP bound to _____
  • release of 2IF2 and other initation facotrs
  • initation factors are then released, and the 60S subunit joins the complex
A

identify AUG initiation codon

when AUG is identified, eLF5 tiggers hydrolysis of GTP bound to elF2

27
Q

“elongation stage of translation”

  1. the mechanism of elongation in prokaryotic and eukaryotic cells is similar
  2. the ribosomes has three binding sites: _____,_________,________-“

the initiator _____________ is bound at ________-
the __________ binds to the _______

A
  1. three binding sites: P (peptidyl) , A (aminoacyl), and E (exit)sites

the initiator METHIONYL tRNA is bound at the P SITE

the NEXT AMINOACYL tRNA bind to the A SITE

28
Q

“elongation stage of translation”

hydrolysis of GTP bound to eEF1a and release of the ________

then the peptide bond is formed, catalyzed by the large ribosomal subunit and the now initator tRNA is at the P site

A

release of the elongation factor

29
Q

“translation of mRNA”

The steps of ___________

  1. ribosome then moves three nucleotides laong the mRNA, positioning the ext codon in an empty A site
  2. This step translocates the peptidyl tRNA from A to P, and the uncharged tRNA from P to E
A

translocation

30
Q

“translation of mRNA”

translocation requires another _____________ (EF-G in prokaryotes and ________ in eukaryotes) and is coupled to _________

A

translation requires another ELONGATION FACTOR (EF-G in prokaryotes, eEF2 in eukaryotes) and is coupled to GTP HYDROLYSIS`

31
Q

“regeneration of eEF1 a GTP”

as elongation continues, the __________ (or EF-Tu) released from the ribosome bound to GDP must be reconverted to its GTP form

this requires another elongation factor, _____ (EF-T in prokaryotes). regulation of eEF1 alpha by GTP binding and hydrolysis is a common method of protein regulation

A

eEF1a

eEF1b

32
Q

“termination of translation”

elongation continues until a _________ ( UAA,UAG, UGA) is translocated into the ____________.

_________ recognize the signals and terminate protein synthesis

in prokaryotic cells RF1 recognizes UAA or UAG, RF2 recognizes UAA or UGA.
in eukaryotic cells eRF1 recognizes all 3 stop codons

A

elongation continues until a STOP CODON is located into the A SITE

RELEASE FACTORS recognize the sigals and terminate protein synthesis

33
Q

mRNAs can be translated simultaneously by several ribsomes. once a ribosome has moved away from the initiation site, another can bind to the mRNA and begin sythesis.
a group of ribsomes bound to an mRNA molecule is called a polyribosome, or a __________

A

polysome`

34
Q

regulation of translation plays a key role in gene expression, include:

  1. ___________________
  2. ___________________

Global translation activity is modulated in response to _____, _____________, ______________.

Example: regulation of ferritin translation (a protein that stores iron) by repressor proteins: when iron is absent, ______________________________ binds to the iron response elements (IRE) in the 5’ UTR, blocking translation

A
  1. translation repressor proteins
  2. noncoding microRNAs

global translational activity is modulated in response to STRESS, NUTRIENT AVAILABILITY, and GROWTH FACTOR STIMULATION.

when iron is absent, IRON REGULATORY PROTEIN (IRP)

35
Q

Some translational repressors bind to specific sequences in the 3’ UTR

some bind to initiation factor eLF4E, interfering with itis interaction with eLF4G and inhibiting initiation of translation

A

General

36
Q

______________________-mediated by short double-stranded RNAs, is used as an experimental tool to block gene expression at the level of translation

A

RNA interference (RNAi)

37
Q

in cells, it is an important mechanism of translational regulation. RNA interference is mediated by: two types of small RNAS mediated RNA interference

small interfering RNAs (siRNAs)- produced from __________ by nuclease Dicer

MicroRNAs (miRNAs)-transcribed by _________________, then cleaved by nucleases Drosha and Dicer

A

doulbe stranded RNAS

RNA polymerase II

38
Q

one strand of miRNA or siRNA is incorporated into an RNA induced silencing complex (RISC)

siRNAs generally pair with their targets and induce cleavage of the mRNA

most miRNAs from ___________ that repress translation

A

mismatches

39
Q

as many as 1000 miRNAs are encoded in mammals; each can target up to 100 different mRNAs

up to one-half of protein-coding genes may require regulatation by __________.

they are important in embryonic development, and may play a role in cancer and other diseases

A

miRNA

40
Q

translation can also be regulated by modification of initiation factors. This results in a global effects on overall translational activity rather than translation of specific _____________

A

mRNAs

41
Q

__________________________ by regulatory ________________ blocks the exchange of bound GDP for GTP, inhibiting initiation of translation

A

phosphorylation of eLF2 and elF2B

protein kinases

42
Q

feedback inhibition is an example of ___________________, in which a regulatory molecule binds to an enzyme site that is distinct from the catalytic site

A

allosteric regulation

43
Q

“phosphorylation and other modifications”

phosphorylation is ________; can activate or inhibit proteins in response to environmental signals

catalyzes by ______________, which transfer phosphate groups from ATP to the hydroxyl groups of side chains of serine, threonine, or tyrosine

A

phosphorylation is reversible

catalyzed by PROTEIN KINASE

44
Q

phosphorylation is reversed by ______________ , which catalyze hydrolysis of phosphorylated amino acids

protein kinases are often components of signal transduction pathways.

Sequential action of a series of protein kinases can transmit a signal from the cell surface to target proteins in the cell, resulting in changes in cell behavior in response to environmental stimuli

A

protein phosphatases

45
Q

Example: in muscle cells epinphrine signals breakdown of glycogen to glucose-1-phosphate, providing energy for increased muscular acitivity

this is catalyzed by _____________ phosphorylase, which is regulated by protein kinase

the signalling pathway is initiated by allosteric regulation-epinephrine binds to cell surface receptor, and cAMP binds to cAMP-dependent kinsase

the sinal is then transmitted to its target by the sequental action of protien kinase

A

catalyzed by glycogen phosphorylase

46
Q

other covalent modifications include:

A

acetylation of lysine

methylation of lysine and arginine

nitrosylation (addiiton of NO groups) to cysteine

glycosylation of serine and threonine

47
Q

some proteins are regulated by covalent attachment of _________.

addition of _____________ and other ubiquitin like proteins, such as __________, affect a variety of function

A

attachment of polypeptides

addition of ubiquitin

such as SUMO

48
Q

addition of ubiquitin (ubiquitylation) is a multistep process

the specificity of ________________________ selectivity targets proteins for degration

A

E3 enzymes

49
Q

“protein- protein interactions”

many proteins consist of multiple subunits; interactions between them can regulate protein activity

Example: cAMP-dependent protein kinase has two _____________ and two __________ subunits in the inactive forms

cAMP binds to the regulatory subunits, which induces conformational change and dissociation of the complex

the free catalytic subunits are then enzymatically active protein kinases

cAMP acts as an allosteric regulator by altering protein-protein interactions

A

cAMP-dependent protein kinase has two REGULATORY and two CATALYTIC subunits in active form

50
Q

protein levels in the cells are determined by rates of __________ and ________

half-lives of proteins vary greatly; differential rates of degradation are important in cell regulation

many regulatory proteins have short half lives; this allows levels to change quickly in response to external stimuli

faulty or damage protein are recognized and rapidly degraded

A

protein levels in cells are determined by RATES OF SYNTHESIS and RATES OF DEGRADATION

51
Q

the major pathway of protein degradation in eukaryotes is the __________________.

________ is highly conserved in all eukaryotes

A

ubiquitin-proteasome pathway

ubiquitin

52
Q

ubiquitin is attached to the amino group of the side chain of a lysine residue, then more are added to form a chain.

polyubiquinated proteins are recognized and degraded by a large protease complex the _________________–

A

the proteasome

53
Q

what are the four stages of mitosis?

A

phrophase

metaphase

anaphase

telophase

54
Q

many proteins that control fundamental cellular processes are targets for regulated ___________ and ____________

example: cyclins that regulate progression through the divsion cycle of eukaryotic cells

A

ubiquitylation and proteolysis

55
Q

entry of cells into mitosis is controlled in part by ___________, a regulatory subunit of Cdk1 protein kinase

the active cyclin B-Cdk1 complex induces entry into ____________

degradation of cyclin B by the proteasome then leads to inactivation of the Cdk1 kinase, allowing the cell to exit mitosis and return into interphase

A

cyclin B

mitosis

56
Q

protein degradation can also take place in _________________- membrane-enclosed organelles that contain digestive enzymes, including proteases

lysosomes digest extracellular proteins taken up by endocytosis, and take part in turnover of organelles and proteins

containment of digestive enzymes in lysosomes prevents uncontrolled degradation of cell contents

proteins move into lysosome by _________; vesicles (autophagosomes) enclose small areas of cytoplasm or organelles and then fuse with lysosomes

A

lysosomes

autogphagy

57
Q

autophagy is activated in nutrient starvation, allowing cells to degrade ____________ and ________ and reutilize the components

autophagy also plays a role in many developmental processes, such as insect metamorphosis, which involve extensive tissue remodeling

A

nonessential proteins

organells

Molecular Cell Biology Jessica (33 decks)

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