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Cell Biology > Ribosomes > Flashcards

Ribosomes Flashcards

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AP® Biology flashcards Biology 101 flashcards
1
Q

How many subunits are ribosomes made up of?

A

2

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2
Q

When are ribosomal subunits joined?

A

When synthesising a protein

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3
Q

What does the ‘S’ of a 70S ribosome stand for?

A

Svedberg unit = sedimentation coefficient

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4
Q

What is a sedimentation coefficient?

A

A measure of how quickly a molecule sediments

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5
Q

Bigger molecules sediment _______ and therefore have a ________ S value

A

Quicker

Higher

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6
Q

What is the structure of a ribosomal subunit?

A

RNA core with proteins attached to the outside

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7
Q

What is the number of proteins attached to the outside of the RNA core of a ribosome dependent on?

A

The length of RNA

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8
Q

Roughly how many ribosomes are there in a cell?

A

1,000,000

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9
Q

Describe the process of ribosome synthesis.

A
  1. rRNA is synthesised in the nucleolus
  2. Ribosomal proteins are synthesised in the cytoplasm
  3. Ribosomal subunits are produced by assembling the rRNA and the ribosomal proteins in the nucleolus
  4. Individal subunits leave the nucleus are pair off to form whole ribosomes during protein synthesis
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10
Q

Where are the genes encoding for rRNA found?

A

On 10 chromosomes in close proximity to each other found in the nucleolus

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11
Q

What is the main function of ribosomes?

A

Translation

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12
Q

Describe the process of translation.

A
  1. mRNA binds to a small subunit
  2. The subunits moves along the mRNA until it reaches the start codon
  3. The large subunit binds
  4. The ribosome matches the tRNA anticodon sequence with the mRNA codon sequence
  5. Each time a new tRNA is incorporated in the anticodon sequence the amino acid attached to it is added the the elongating polypeptide
  6. When the mRNA subunit reaches the stop codon the release factor will bind to the mRNA
  7. The polypeptide chain is released
  8. The two subunits dissocaite
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13
Q

What is a typical start codon?

A

AUG

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14
Q

What is a typical stop codon?

A

TAA
TAG
TGA

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15
Q

What three sites are found within the large subunit?

A

E - site
P - site
A - site

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16
Q

What happens at the E-site in the large subunit?

A

Uncharged tRNA exits the ribosome

17
Q

What happens at the P-site in the large subunit?

A

Peptidyl tRNA is formed

18
Q

What happens at the A-site in the large subunit?

A

Aminoacyl tRNA enters = charged tRNA

19
Q

What does ribozyme do?

A

Catalyses the formation of peptide bonds between adjacent amino acids

20
Q

What are polyribosomes?

A

Multiples ribosomes bound to the same piece of mRNA

21
Q

Why might proteins require degradation?

A

Misfolded
Aged
Damaged

22
Q

What component of the cell is responsible for the degradation of proteins?

A

Proteasomes

23
Q

What is the structure of a proteasome?

A

Hollow tube of many subunits containing ATP dependent proteases
Cap structures at either end act as gateways and have ATPase activity = this unfolds target proteins

24
Q

How long is a substrate retained in the proteasome tube for?

A

Until it is broken down into small peptides

25
Q

What molecule is responsible of regulating the degradation of proteins?

A

Ubiquitin

26
Q

What is ubiquitin?

A

A short peptide which attaches to the NH2 side chain of lysine residues in proteins targeted for degradation

27
Q

What do ubiquitin activating enzymes do?

A

Catalyse the transfer of ubiquitin ligase to proteins to be degraded

28
Q

What molecule recognises proteins targeted for degradation?

A

Ubiquitin ligase E2/E3 complex

29
Q

What happens when ubiquitin ligase recognises a protein to be degraded?

A
  • Ubitquitin ligase is transferred to the protein (catalysed by ubiquitin activating enzymes)
  • The ubiquitin dissociates from the ligase and binds to the protein
  • Further ubiquitin molecules are added to the target protein
30
Q

What is the signal for proteasomes to degrade a protein?

A

Multiple ubiquitin chains present on the protein

Cell Biology (11 decks)

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