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A-level Chemistry > PL - Protein synthesis > Flashcards

PL - Protein synthesis Flashcards

1
Q

What does DNA contain?

A

The basis of the genetic code.

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2
Q

What does RNA do with the genetic code/DNA?

A

Takes it and turns it into proteins.

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3
Q

In terms of protein synthesis and proteins, what does DNA contain?

A

The codes and instructions for building all the proteins in an organism.

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4
Q

What is each protein coded for by?

A

A separate section of DNA called a gene.

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5
Q

What are proteins made up of?

A

A sequence of amino acids.

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6
Q

What do genes contain?

A

Information about what order amino acids should go in in a protein.

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7
Q

How do genes control the order of amino acids in a protein?

A

1) DNA codes for specific amino acids with sequences of 3 bases, called base triplets or codons. Different sequences of bases code for different amino acids.
2) There are 64 possible base triplet combinations, but only about 20 amino acids in humans proteins so there are some base triplets to spare. These aren’t wastes though as some amino acids have more than one base triplet code, and some base triplets act as ‘punctuation’ to stop and start production of an amino acid chain (start and stop codons).
3) The order in which the amino acids are connected together (the primary structure) determines the secondary and tertiary structures of a protein - and so all the protein’s properties.

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8
Q

What is a sequence of 3 bases called?

A

Base triplets or codons.

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9
Q

How many possible base triplet combinations are there?

A

There are 64 possible base triplet combinations, but only about 20 amino acids in humans proteins so there are some base triplets to spare.

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10
Q

What happens to the base triplet combinations that do not code for amino acids/that aren’t one of the 20 amino acids in humans?

A

They aren’t wasted:

  • Some amino acids have more than one base triplet code, for example serine is coded for by the triplet AGT (or UCA in mRNA), and also by the triple AGC ( or UCG in mRNA).
  • Some base triplets act as ‘punctuation’ to stop and start production of an amino acid chain (called start and stop codons).
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11
Q

What are triplets that act as punctuation instead of coding for an amino acid called?

A

Start or stop codons.

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12
Q

What do start and stop codons do?

A

Act as ‘punctuation’ to stop and start production of an amino acid chain

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13
Q

What does RNA help do?

A

Turn the genes in DNA into proteins.

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14
Q

What are the three types of RNA?

A 
Messenger RNA (mRNA).
Transfer RNA (tRNA).
Ribosomal RNA (rRNA).
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15
Q

What is mRNA?

A

A single polynucleotide strand which is an exact copy of a single strand section of DNA, expect thymine’s replaced by uracil.

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16
Q

How many polynucleotide strands in mRNA?

A

1

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17
Q

What is mRNA an exact copy of?

A

A single strand section of DNA, expect thymine’s replaced by uracil.

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18
Q

What are the amino acid codons in mRNA complementary to?

A

The DNA codons.

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19
Q

Why are the amino acid codons in mRNA complementary to the DNA codons?

A

As they form when complementary bases pair up.

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20
Q

Give an example of why/how the amino acid codons in mRNA are complementary to the DNA codons

A

For example, leucine has an mRNA codon of CUG and aspartic acid has an mRNA codon GAU. The dipeptide LeuAsp will be coded for by an mRNA sequence if CUGGAU. The DNA that codes for this section of mRNA will be complementary base pairs: GACCTA.

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21
Q

What is tRNA?

A

A single polynucleotide strand that’s folded into a clover shape.

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22
Q

What does mRNA stand for?

A

Messenger RNA.

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23
Q

What does tRNA stand for?

A

Transfer RNA.

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24
Q

What does rRNA stand for?

A

Ribosomal RNA.

25
Q

How many polynucleotide strands is tRNA?

A

1

26
Q

What shape is tRNA?

A

Clover shape.

27
Q

Describe the structure of tRNA

A

It is folded into a clover shape.

At one end of the tRNA molecule there’s a sequence of 3 base pairs called an anticodon. The anticodon complements a codon on the mRNA, so will attach to parts of the mRNA, where that codon is present by base pairing.

At the other end of the tRNA there’s a binding site where the amino acid that corresponds to the complementary mRNA codon can attach.

28
Q

How do mRNA and tRNA relate?

A

At one end of the tRNA molecule there’s a sequence of 3 base pairs called an anticodon. The anticodon complements a codon on the mRNA, so will attach to parts of the mRNA, where that codon is present by base pairing.

At the other end of the tRNA there’s a binding site where the amino acid that corresponds to the complementary mRNA codon can attach.

29
Q

What is an anticodon in tRNA?

A

A sequence of 3 base pairs that is complementary to a codon on the mRNA.

30
Q

What happens at the binding site of tRNA?

A

The amino acid that corresponds to the complementary mRNA codon can attach.

31
Q

What happens at the anticodon of tRNA?

A

It complements a codon on the mRNA, so will attach to parts of the mRNA, where that codon is present by base pairing.

32
Q

What is rRNA?

A

It is made up of polynucleotide strands that are attached to proteins to make things called ribosomes.

33
Q

What is the largest type of RNA?

A

rRNA.

Ribosomal RNA.

34
Q

What is the function of rRNA?

A

It is made up of polynucleotide strands that are attached to proteins to make things called ribosomes.

35
Q

What are the polynucleotide strands that make up rRNA attached to and why?

A

They are attached to proteins to make ribosomes.

36
Q

mRNA is made using what as a template?

A

DNA

37
Q

What is the process which makes mRNA called?

A

Transcription.

38
Q

What is the first stage of protein synthesis?

A

Transcription.

39
Q

Which type of RNA is first needed in protein synthesis?

A

mRNA.

40
Q

What type of RNA is made in/through transcription?

A

mRNA.

41
Q

Describe the process of transcription

A

1) The DNA double helix unwinds to reveal a single stranded portion.
2) The DNA bases attract free RNA nucleotides with complementary bases.
3) The RNA nucleotides are joined to each other by the enzyme RNA polymerase. This forms a strand of mRNA.
4) The DNA coils up again, unaltered.

The newly made mRNA strand does not wind up with the DNA - it is released and is free to move around the cell. It is small enough to move outside the cell’s nucleus into the cytoplasm, where it is used in translation.

42
Q

What enzyme joins the RNA nucleotides to each other in transcription?

A

RNA polymerase.

43
Q

What happens to the mRNA formed in transcription?

A

The newly made mRNA strand does not wind up with the DNA - it is released and is free to move around the cell. It is small enough to move outside the cell’s nucleus into the cytoplasm, where it is used in translation.

44
Q

What are made during translation?

A

Proteins.

45
Q

What happens in translation?

A

Amino acids are joined together to make a polypeptide chain.

46
Q

Which types of RNA are used in translation?

A

mRNA, tRNA and rRNA - so all of them!

47
Q

Describe the process of translation

A

1) DNA transcription occurs to make a strand of mRNA.
2) Ribosomes are large complexes made from rRNA and proteins. A ribosome attaches to the mRNA, and starts to move along it, looking for a start codon (AUG - methionine).
3) Once it’s found a start codon, the ribosome temporarily pauses, until a tRNA with the correct anticodon base pairs with the AUG codon inside the ribosome. The tRNA has methionine amino acid attached to it.
4) The ribosome then moves 3 bases forward, and waits for a different tRNA to bring the next amino acid that the mRNA codes for into the ribosome. Now there are 2 amino acids inside the ribosome and the ribosome joins them together with a peptide bond.
5) The ribosome moves forwards again. The first tRNA now leaves the ribosome and breaks away from its amino acid. A new tRNA brings in the third amino acid of the chain.
6) The process continues in this way until a stop codon is reached. The stop codon doesn’t code for an amino acid. The ribosome releases the polypeptide chain at this point.

48
Q

What is the second stage of protein synthesis?

A

Translation.

49
Q

What is a codon/base triplet?

A

A sequence of three bases that codes for an amino acid.

50
Q

What base sequence do start codons have?

A

AUG - methionine amino acid.

51
Q

What do start codons do?

A

Indicate that the code for a new polypeptide chain is beginning. They code for the first amino acid in the chain (so this is always the same - AUG so it’s methionine).

52
Q

What are ribosomes?

A

Large complexes made from rRNA and proteins.

53
Q

What are ribosomes made from?

A

rRNA and proteins.

54
Q

What does the ribosome attach to in translation?

A

mRNA.

55
Q

What happens in translation when a stop codon is reached?

A

The stop codon doesn’t code for an amino acid so the ribosome releases the polypeptide chain at this point.

56
Q

What bond forms between two amino acids in translation?

A

A peptide bond.

57
Q

What is formed when two amino acids are joined together?

A

A dipeptide joined by a peptide bond.

58
Q

Where in the cell does translation occur?

A

In the cytoplasm.

59
Q

Where does transcription occur?

A

In the nucleus.

A-level Chemistry (51 decks)

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