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Karan - MBBS Year 1: Principles Week 3 > Protein Synthesis > Flashcards

Protein Synthesis Flashcards

1
Q

What is the genetic code?

A
  • Determine how RNA code is converted to amino acid sequences
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2
Q

What are the rules for the genetic code?

A
  • Code is degenerate and unambiguous
  • Code is non-overlapping
  • Start codon AUG sets reading frame and ends with stop codon UGA, UAG, UAA
  • Order of codons in mRNA determines amino acid sequence
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3
Q

What does it mean for the genetic code to be degenerate and unambiguous?

A
  • Amino acids - more than 1 codon
  • Each codon specifies only 1 amino acid
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4
Q

What does it mean for the code to be non-overlapping?

A
  • Each nucleotide only read once
  • Codons read sequentially
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5
Q

What causes mutations and what can they cause?

A
  • Occur because of DNA damage and DNA replication errors
  • Transcribed to mRNA - results in proteins with abnormal sequences
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6
Q

What are the three types of point mutations?

A
  • SILENT - Single base change - produces same amino acid
  • MISSENSE - SIMILAR TO SILENT - produces different amino acid
  • NONSENSE - Change forms premature stop codon
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7
Q

What are the two types of frameshift mutations?

A
  • INSERTION - ADDITION of 1 or more bases - protein with more amino acids
  • DELETION - REMOVAL of 1 or more bases - protein with fewer amino acids
  • Cause shift of reading frame - amino acid sequence altered
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8
Q

Outline initiation

A
  • mRNA migrates to and binds to ribosome
  • tRNA carries specific amino acid to ribosome
  • Anticodon on tRNA binds to mRNA codon
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9
Q

TWO TY

Outline elongation and terminastion.

A
  • Ribosome catalyses amino acid bonding to adjacent aa to form polypeptide chain
  • tRNA releases
  • Ribosome reaches stop codon - translation ends/polypeptide chain released
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10
Q

What is tRNA?

A
  • Adaptor molecule - carries amino acid to ribosome and binds to codon
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10
Q

What are the 4 key regions of a tRNA molecule?

A
  • Acceptor stem - carries amino acid at 3’ CCA end
  • Anticodon - associate with mRNA coodon by complementary base pairing
  • T arm - associate with ribosome at E,P and A sites
  • D arm - associate with tRNA activating enzyme
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11
Q

Outline eukaryotic ribosomal structure.

A
  • Made up of rRNA: 60S and 40S subunits
  • A site - binds tRNA carrying amino acid
  • P site - binds tRNA attached to growing peptide chain
  • E site - releases tRNA carrying last amino acid
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11
Q

Outline chain initiation. PART 1

A
  • Initiator tRNA-methionine (UAC) loaded onto 40S subunit, with eukaryotic initiation factors (eIFs)
  • 40S binds to 5’ end of mRNA by recognizing 5’ cap
  • mRNA scanned from 5’-3’ for start codon
  • Translation begins at start codon AUG, eIFs dissociate
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12
Q

Outline chain initiation. PART 2

A
  • 60S assembles to complete ribosome
  • Initiator tRNA-Met is bound to P-site, A-site vacant
  • Aminoacyl tRNA binding
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13
Q

Outline chain elongation. PART 1

A
  • 2nd complementary tRNA binds to vacant A site
  • Met in P site covalently attach to amino acid in A site (catalyzed by peptidyl transferase in 50S)
  • tRNA in P site is deacylated and peptide chain is in A site
  • Ribosome translocate (5’- 3’) and shift tRNAs to E and P sites (via EF and GTP hydrolysis)
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14
Q

Outline chain elongation. PART 2

A
  • tRNA is released from E site
  • Peptide chain is in P site
  • A site is open for next aminoacyl-tRNA
  • Polypeptide is built from N-terminal to C-terminal direction
15
Q

Outline chain termination.

A
  • Stop codons signal to ribosome to stop translation
  • Release factor (RF) bind to A site on stop codon
  • Carboxyl end of the polypeptide chain is freed from tRNA
  • Completed chain is released into the cytoplasm
  • Ribosome releases mRNA and dissociates into its subunits
16
Q

What are polysomes?

A
  • Structures in prokaryotes where multiple ribosomes simultaneously translate a single mRNA
17
Q

Describe protein folding.

A
  • N-terminal folds whilst C-terminal still synthesising
  • Molecular chaperons bind to hydrophobic residues and make folding more efficient
18
Q

Describe post-translational modifications.

A
  • Cleavages e.g of Met at N-terminal activate protein
  • Increase protein stability
  • Signal sequence added to protein to direct it to a cellular component
19
Q

Give examples of post-translational modifications.

A
  • PHOSPHORYLATION
  • HYDROXYLATION
  • METHYLATION
  • GLYCOSYLATION
20
Q

Describe proteasome-mediated protein degradation.

A
  • Abnormal/misfolded proteins tagged with ubiquitin degraded by proteasomes
21
Q

Describe the process of transporting signal peptides to their desired destinations.

A
  • SRP binds to signal peptide and translation pauses
  • Polypeptide transported to ER where translation continues
  • Protein transported to Golgi apparatus and sent to target destinations.

Karan - MBBS Year 1: Principles Week 3 (10 decks)

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