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MD2S3: Molecular Biology > Protein Synthesis and Post Translational Modifications > Flashcards

Protein Synthesis and Post Translational Modifications Flashcards

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1
Q

What are the steps of Protein Synthesis?

A

Initiation
Elongation
Termination
Translation Regulation
Protein Folding
Protein Targeting

Transcription and Translation are temporally linked in Prokaryotes due to the lack of a Nuclear Membrane

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2
Q

Initiation
Purpose

A

Assembly of Translation System Components

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3
Q

Initiation
Components of Translation System

A

Two Ribosomal Subunits
mRNA
Aminoacyl-tRNA
GTP
Initiation Factors
Eukaryotes require ATP

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4
Q

Initiation
Function of Initiation Factors

A

Assembly of Initiation Complex

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5
Q

Initiation
Names of Initiation Factors in Prokaryotes and Eukaryotes

A

Prokaryotes: IF-1, IF-2, IF-3
Eukaryotes: Multiple Initiation Factors

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6
Q

Initiation: E. Coli
Location of Shin-Dalgarno Sequence

A

6 to 10 b.p. upstream of AUG initiation codon of mRNA

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7
Q

Initiation: E. Coli
The Shin-Dalgarno Sequence enables ____ because the ____

A

__positioning of 30S subunit__
__16S rRNA component of 30S Ribosomal Subunit complementary to SD__

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8
Q

Initiation: Eukaryotes
How is initiation AUG located?

A

40S subunit and eIF-4 proteins bind to cap structure
Move in 5’-3’ direction along mRNA until it reaches AUG
Scanning requires ATP

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9
Q

Initiation
Which tRNA recognizes initiator AUG?

A

tRNAi (Initiating tRNA)

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10
Q

Initiation
Recognition by tRNAi is facilitated by ____ in prokaryotes and ____ in eukaryotes

A

__IF-2-GTP__
__eIF-2-GTP__

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11
Q

Initiation
Which Antibiotic interferes with Prokaryotic Initiation?

A

Streptomycin binds to 30S subunit

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12
Q

Initiation
Modifications of tRNAi in Bacteria and Mitochondria

A

Met attached to tRNA
Formyl group added by enzyme
Forms tRNAi carrying N-Formylated Methionine (fMet)

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13
Q

Initiation
Modifications of tRNAi in Eukaryotes

A

tRNAi carries Met that is not formylated

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14
Q

Initiation
In Prokaryotes and Eukaryotes ____ is removed before translation completion

A

__N-Terminal Met__

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15
Q

Initiation
What is the final stage of Initiation?

A

Charged tRNA moved from A site to P site (2 high energy bonds consumed)
Large Ribosomal Subunit (50S in Prokaryotes and 60S in Eukaryotes) joins forming 70S (Prokaryotes) or 80S (Eukaryotes)

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16
Q

Elongation
Purpose

A

Addition of Amino Acids to the Carboxyl end of the Growing Chain

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17
Q

Elongation
Process

A

Decoding
Peptide bond formed between amino acids of A and P sites
Transpeptidation
Translocation

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18
Q

Elongation
What is Decoding?

A

Addition of Aminoacyl tRNA to next codon of mRNA template in ribosomal A site

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19
Q

Elongation
What does decoding require?

A

Elongation Factors
GTP

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20
Q

Elongation
The ____ enzyme catalyses the peptide bond formation between ____ groups of amino acids at the A and P site

A

__peptidyl transferase__
__α-carboxyl group__

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21
Q

Elongation
Category of Peptidyl Transferase enzyme

A

23rRNA of 50S subunit

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22
Q

Elongation
What is Transpeptidation?

A

Peptide of tRNA at P site transferred to amino acid on tRNA at A site

23
Q

Elongation
What is Translocation?

A

Advancement of Ribosome by three Nucleotides

24
Q

Elongation
Describe the process of Translocation

A

Uncharged tRNA moves from P to E site where it is released
Peptidyl-tRNA moves from A to P site
Process continues until Termination Codon is reached

25
Q

Elongation
What is required for the Translocation process?

A

GTP hydrolysis

26
Q

Elongation
What drug inhibits Peptide Bond formation?

A

Chloramphenicol inhibits Prokaryotic Petidyl Transferase

27
Q

Elongation
Which drug binds to the peptide of the P site?

A

Puromycin inhibits Elongation in Prokaryotes and Eukaryotes as it resembles Aminoacyl tRNA and accepts peptide from P site

28
Q

Elongation
Which drug inhibits Translocation?

A

Erythromycin binds to 50S subunit in Prokaryotes inhibiting Translocation

29
Q

Elongation
Which drug restricts access to A site?

A

Tetracyclines interact with 30S to stop aminoacyl tRNA entering A site

30
Q

Termination
What are the three Termination Codons?

A

UAA
UAG
UGA

31
Q

Termination: E. Coli
Release Factors + Functions

A

RF-1 and RF-2: Recognize Termination Codons and Hydrolyze bonds linking Peptides to tRNA
RF-3: Causes release of RF-1 and RF-2 as GTP

32
Q

Termination: Eukaryotes
Release Factors + Functions

A

eRF: Recognizes Termination Codons
eRF-3: Same function as RF-3

33
Q

What are the methods of Translation Regulation?

A

Prokaryotes and Eukaryotes: Proteins bind to mRNA blocking translation
Eukaryotes: eIF-2 is Phosphorylated making it inactive

34
Q

How does Protein Folding occur?

A

Spontaneous or Facilitated by Chaperone Proteins

35
Q

Protein Targeting
How are Proteins directed to their final locations?

A

Amino acid sequences in the protein

36
Q

Protein Targeting
Pathway of Intracellular Processing of Protein

A

Protein moves through RER and Golgi

37
Q

Protein Targeting
What is Co- and Post-Translational Modification?

A

Co-Translational Modification: Modification of Polypeptide while still attached to ribosome
Post-Translational Modification: Modification of Polypeptide after completion of synthesis

38
Q

Protein Targeting
What are the types of Protein Targeting?

A

Trimming
Covalent Attachment
Protein Degradation

39
Q

Protein Targeting: Trimming
What is Trimming?

A

Removal of Portions of Proteins by Endoproteases in RER, Golgi, Secretory Vesicles or After Secretion

40
Q

Protein Targeting: Trimming
Purpose of Trimming

A

Cleaves Precursor Molecules into Functionally Active Molecules

41
Q

Protein Targeting: Covalent Modifications
What are the types of Covalent Modifications?

A

Phosphorylation
Glycosylation
Hydroxylation
Carboxylation

42
Q

Protein Targeting: Covalent Modifications
Phosphorylation: Definition

A

Addition or Removal of Phosphate Group on the Hydroxyl Group of Serine, Threonine and Tyrosine Residues

43
Q

Protein Targeting: Covalent Modifications
Phosphorylation: Addition catalysed by ____ and removal by ____

A

__Protein Kinase__
__Protein Phosphatase__

44
Q

Protein Targeting: Covalent Modifications
Phosphorylation: Function

A

Increases/decreases functional activity of proteins

45
Q

Protein Targeting: Covalent Modifications
Glycosylation: Definition

A

Addition of Carbohydrate Chain to terminal ends of amino acid

46
Q

Protein Targeting: Covalent Modifications
Glycosylation: Types

A

N-linked: Carbohydrate chain attached to Amide Nitrogen of Aspirigine
O-linked: Carbohydrate chain attached to Hydroxyl Groups of Serine, Threonine and Hydroxylysine

47
Q

Protein Targeting: Covalent Modifications
Glycosylation: N-Linked Glycosylation occurs in …

A

RER

48
Q

Protein Targeting: Covalent Modifications
Glycosylation: O-Linked Glycosylation occurs in …

A

Golgi Apparatus

49
Q

Protein Targeting: Covalent Modifications
Hydroxylation: Definition

A

Hydroxylation of Proline and Lysine Residues of Collagen

50
Q

Protein Targeting: Covalent Modifications
Hydroxylation: Catalysed by …

A

Vitamin-C Dependent Hydroxylases

51
Q

Protein Targeting: Covalent Modifications
Hydroxylation: Location

A

RER

52
Q

Protein Targeting: Covalent Modifications
Carboxylation: Definition

A

Carboxyl Groups added to Glutamate Residues by Vitamin K-Dependent Carboxylation

53
Q

Protein Targeting: Covalent Modifications
Carboxylation: Function

A

Y-Carboxyglutamate Residues enable activity of Blood Clotting Proteins

54
Q

Protein Targeting: Protein Degradation
What happens to defective proteins?

A

Ubiquitins mark proteins for destruction by Proteasome

MD2S3: Molecular Biology (10 decks)

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