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AQA A level Biology > Protein synthesis > Flashcards

Protein synthesis Flashcards

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1
Q

What are the 2 steps involved in protein synthesis

A
  • Transcription
  • Translation
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2
Q

Define transcription

A

Where one gene of the DNA is copied into mRNA

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3
Q

Define translation

A

Where the mRNA joins with a ribosome, and corresponding tRNA molecules brings the specific amino acid the codon codes for

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4
Q

Where does transcription happen within the cell

A

Inside the nucleus

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5
Q

Why do we have the create a copy of the gene of interest on the DNA for protein synthesis (2 reasons)

A
  • Because DNA is too big to leave the nucleus
  • There are enzymes in the cytoplasm that could damage the DNA
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6
Q

How come mRNA is small enough to leave the nucleus but DNA isn’t

A

Because mRNA carries the code for one gene whereas DNA carries the code for all the genes

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7
Q

What is the first step in transcription, and name the enzyme

A

The DNA HELIX UNWINDS to expose the bases to act as a template - unwinding is catalysed by DNA HELICASE

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8
Q

During transcription, how many chains of DNA act as a template, and why is this

A

Only one because mRNA is single stranded

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9
Q

What type of bonds does DNA helicase break between the bases

A

Hydrogen bonds

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10
Q

Once DNA helicase has unzipped the DNA strand, what do the free mRNA nucleotides do

A

They align opposite exposed complementary DNA bases

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11
Q

What is the name of the enzyme that bonds together RNA nucleotides to create a new RNA polymer chain

A

RNA polymerase

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12
Q

What bonds form between the RNA nucleotides uses the enzyme RNA polymerase

A

Phosphodiester bonds

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13
Q

What process occurs to change pre-mRNA to mRNA

A

Splicing

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14
Q

What happens during splicing

A

The introns are removed

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15
Q

What are introns

A

The sequences of bases in the DNA which don’t code for amino acids

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16
Q

What is the name of the enzyme involved in splicing

A

Splicesome

17
Q

What bonds does the splicesome break

A

The phosphodiester bonds

18
Q

Does mRNA contain any introns

A

No, it only contains exons- the coding part of DNA

19
Q

What happens during translation

A

The polypeptide chain is created using both the mRNA base sequence and the tRNA

20
Q

Once the mRNA has left the nucleus where does it go

A

It attaches to a ribosome in the cytoplasm

21
Q

What does the tRNA molecule with the complementary anticodon to the start codon do

A

It aligns opposite the mRNA, held in place by the ribosome

22
Q

What is the role of the ribosome during translation

A

To hold the mRNA and tRNA molecules in place

23
Q

Once the tRNA that has complementary anticodon to the codon on mRNA has aligned, what does the ribosome do

A

It moves along the mRNA, so another tRNA molecule can align

24
Q

How many tRNA molecules can the ribosome hold at one time during translation

A

Two

25
Q

When there are 2 tRNA molecule aligned with the mRNA molecule, what happens to their amino acids before the ribosome releases it, and what is required for this to happen

A

The amino acids are joined by a peptide bond- this is catalysed by an enzyme and requires ATP

26
Q

Can tRNA molecules be reused

A

Yes, after they have detached from the ribosome than enter the cytoplasm again and can be reused

27
Q

What codon is required at the end of the mRNA molecule to stop translation

A

The stop codon

28
Q

How does the stop codon end translation

A

Because it doesn’t code for an amino acid and therefore the ribosome detaches since there isn’t a corresponding anticodon on a tRNA molecule

29
Q

After translation, where does the polypeptide chain go and what happens

A

It enters the Golgi body for folding and modification

30
Q

When reading a base sequence wheel, what sequence does it read for; DNA, mRNA, or tRNA

A

mRNA

31
Q

Describe 2 differences between the structure of a tRNA molecule and the structure of an mRNA molecule

A
  • tRNA is clover leaf shape, mRNA is linear
  • tRNA has hydrogen bonds, mRNA does not
  • tRNA has an amino acid binding site, mRNA does not
  • tRNA has anticodon, mRNA has codon
32
Q

Describe and explain the difference in the structure of pre-mRNA and mRNA (2 marks)

A
  • mRNA has fewer nucleotides
  • Because of splicing
33
Q

Describe how one amino acid is added to a polypeptide that is being formed at a ribosome during translation (3 marks)

A
  • tRNA brings specific amino acid to ribosome
  • Anticodon on tRNA binds to codon on mRNA
  • Amino acids join by condensation reaction/ join by forming a peptide bond
34
Q

Describe how mRNA is produced from an exposed template strand of DNA, not including DNA helicase or splicing (3 marks)

A
  • Free RNA nucleotides form complementary base pairs
  • Phosphodiester bonds form
  • By action of RNA polymerase
35
Q

Describe how mRNA is formed by transcription in eukaryotes (5 marks)

A
  • Hydrogen bonds between DNA bases break
  • Only one strand acts as a template
  • Free RNA nucleotides align by complementary base pairing
  • In RNA uracil base pairs with adenine
  • RNA polymerase joins adjacent RNA nucleotides
  • By phosphodiester bonds
  • Pre-mRNA is spliced
36
Q

Describe how a polypeptide is formed by translation of mRNA (6 marks)

A
  • mRNA attaches to ribosomes
  • tRNA anticodon binds to complementary mRNA codon
  • tRNA brings specific amino acid
  • Amino acid joins by peptide bond
  • Amino acids join together with the use of ATP
  • tRNA released
  • The ribosome moves along the mRNA to form the polypeptide
37
Q

What is the proteome of a cell

A

Range of different proteins that a cell is able to produce

38
Q

Starting with mRNA in the cytoplasm, describe how translation leads to the production of a polypeptide (5 marks)

A
  • mRNA associates with a ribosome
  • Ribosome moves to the start codon
  • tRNA brings specific amino acid
  • Anticodon to codon
  • Ribosome moves along to next codon
  • Amino acids join by peptide bonds
39
Q

Describe the role of a ribosome in the production of a polypeptide (3 marks)

A
  • mRNA binds to ribosome
  • 2 codons
  • tRNA with anticodons to bind
  • Formation of peptide bonds between 2 amino acids
  • Moves along mRNA to next codon

AQA A level Biology (35 decks)

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