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MED 109- BIOLOGY II > 28. RIBOSOMES > Flashcards

28. RIBOSOMES Flashcards

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1
Q
  1. What do Ribosomes consist of?
A
  • they consist of proteins
  • they consist of Ribosomal RNA
  • they consist of 2 Ribosomal sub units
  • a large and a small one
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2
Q
  1. What do Ribosomes do?
A
  • they facilitate base pairing
  • this pairing happens between the tRNA anti codons
    and the mRNA codons
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3
Q
  1. What can be said about the effects of certain antibiotic drugs?

SUCH AS: Tetracycline and Streptomycin

A
  • they can inactivate prokaryotic ribosomes
  • they cannot inactivate eukaryotic ribosomes
  • these drugs can be used to treat bacterial infections
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4
Q
  1. List the features of the Prokaryotic Ribosome Structure?

S= sedimentation coefficient

A
  1. They are 70 S large
  2. They have 2 subunits
  3. The small subunit is 30 S large
    • it has 16S rRNA
    • it has 21 proteins
  4. The large subunit is 50 S
    • it has 28S rRNA
      - it has 31 proteins
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5
Q
  1. List the features of the Prokaryotic Ribosome Structure?

S= sedimentation coefficient

A
  1. They are 80 S large
  2. They have 2 subunits
  3. The small subunit is 40 S large
    • it has 18S rRNA
    • it has 33 proteins
  4. The large subunit is 60 S
    • it has 38.8 S rRNA
      - it has 46 proteins
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6
Q
  1. How many binding sites does a Ribosome have for tRNA?
A
  • it has 3
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7
Q
  1. Name the 3 binding sites that a ribosome has for tRNA?
A
  1. THE P SITE:
    - holds the tRNA that has the growing polypeptide
    chain
    - this is the Peptidly-tRNA binding site
  2. THE A SITE:
    • holds the tRNA that carries the next amino acid
    • this amino acid will be added to the chain
    • this is called the Amino Acyl tRNA binding site
  3. THE E SITE:
    • this is where discharged tRNAs leave the ribosome
    • this is the Exit
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8
Q
  1. What are the 3 different kinds of ribosomes that we get?
A
  1. Free Ribosomes
  2. Bound Ribosomes
  3. Polyribosomes
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9
Q
  1. What are Free Ribosomes?
A
  • they are ribosomes that are found in the cytosol
  • they are not bound to the Endoplasmic Reticulum
  • they assist in the synthesis of Cystosolic Proteins
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10
Q
  1. What are Bound Ribosomes?
A
  • they are bound to the Endoplasmic Reticulum
  • they assist in the synthesis of secreted proteins
  • they assist in the synthesis of membrane bound
    proteins
  • EG: ER, Golgi, Plasma Membrane, Organelle Membrane
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11
Q
  1. What are Polyribosomes?
A
  • these are groups of free ribosomes in the cytosol
  • they enable the cell to make many copies of a
    polypeptide quickly
  • each mRNA is translated simultaneously by many
    ribosomes
  • or by polyribosomes
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12
Q
  1. In which direction does Translation occur?
A
  • Translation occurs in the 5’ -3’ directiom
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13
Q
  1. How many nucleotides can you find per ribosome?
A
  • 80 nucleotides
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14
Q
  1. What is the direction of Polypeptide synthesis?
A
  • it goes from the N terminal to the C terminal
  • this goes from the amino terminal end
  • to the carboxyl terminal end
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15
Q
  1. What are the 3 stages of Translation?
A
  1. Initiation
  2. Elongation
  3. Termination
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16
Q
  1. What happens during Initiation?
A
  • the small ribosomal subunit binds with the mRNA
  • it also binds with the initiator (tRNAi)
  • the small subunit will move along the mRNA
  • it does this until it reaches the start codon (AUG)
17
Q
  1. What is the Start Codon?
A
  • the AUG

IN EUKARYOTES:
- this is when the initiator tRNA is couple to Methionine
- the Methionine at the N terminal is removed at the end
of translation

IN PROKARYOTES:
- this is when the initiator tRNA is coupled with Formyl-
methionine (fMet)

18
Q
  1. What do the Initiation Factors (IFs) do?
A
  • they induce the binding of the large ribosomal subunit
  • they also cause the formation of the translation
    initiation complex
  • mRNA + tRNAi + ribosome large and small units
  • GTP provides the energy for this complex to assemble
19
Q
  1. How does the Initiation of Translation happen in Bacteria?
A
  • the small ribosomal subunit binds to the Shine-
    Dalgarno Sequence
  • 5’-AGGAGGU-3’
  • this is located upstream from the start codon (AUG)
  • the AUG is placed at the P site of the Ribosome
20
Q
  1. How does the Initiation of Translation happen in Eukaryotes?
A
  • the small ribosomal sub-unit binds to the 5’cap on the
    mRNA strand
  • this then recognises the Start Codon (AUG)
  • the start Codon is located with the Kozak Sequence
    (5’-ACCAUG G-3’)

MED 109- BIOLOGY II (90 decks)

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