Protein Synthesis

Question 1

Where are DNA molecules found in eukaryotic cells?

Answer 1

• Nucleus

- Mitochondria

Question 2

Where are organelles making proteins found?

Answer 2

Cytoplasm

Question 3

What is the purpose of mRNA?

Answer 3

Carries genetic code from the DNA in the nucleus [too big to leave nuclear pores] to cytoplasm for translation

Question 4

Where is mRNA made?

Answer 4

In nucleus during transcription

Question 5

Where is tRNA found?

Answer 5

Cytoplasm

Question 6

Describe a tRNA molecule - 3

Answer 6

• Amino acid binding site at one end
• Sequence of 3 bases at the other end [anticodon] specific to amino acid its carrying
• Polypeptide folded by hydrogen bonds

Question 7

What is the anticodon sequence?

Answer 7

Triplet of bases complimentary to the mRNA codon for a particular amino acid

Question 8

What is the purpose of tRNA?

Answer 8

Carries amino acids used to make proteins to the ribosomes during translation

Question 9

What is the purpose of a DNA template strand?

Answer 9

To act as a template to be transcribed to make an mRNA complimentary base strand

Question 10

What is a ribosome formed from?

Answer 10

RNA and proteins

Question 11

What is the purpose of transcription?

Answer 11

Converts DNA strand to mRNA complimentary strand

Question 12

What is the purpose of translation?

Answer 12

Amino acids are joined up to form polypeptide chain following the sequence of codons in an mRNA strand

Question 13

Explain how a mutation in the genetic code can cause a non functional protein

Answer 13

• Change to DNA triplet during replication
• Changes to mRNA codon
• So different anticodon needed: so different amino acid
• Changes primary structure of protein
• Different bonding e.g hydrogen/ionic bonds
• Changes tertiary structure
• Doesn’t carry out function

Question 14

Explain how mutations can occur and there still be a functional protein produced

Answer 14

• DNA is degenerate
• Each amino acid is coded for by more than one triplet codon
• Change to DNA base e.g substitution may not cause change to amino acids in primary structure
• No change to bonding and therefore tertiary structure

Question 15

Where does transcription take place?

Answer 15

The nucleus

Question 16

Explain the process of transcription - 10

Answer 16

• RNA polymerase attaches to DNA at start codon
• DNA helicase seperates the DNA strands
• Breaks hydrogen bonds
• One of the strands becomes the template strand
• RA polyermase lines up free RNA nucleotides along side template strand
• RNA nucleotides pair up with specific bases on DNA strand by complementary base pairing and joined together by RNA polymerase
• Forms mRNA molecule
• Hydrogen bonds reform between DNA strands, winds back into double helix
• RNA polymerase reaches stop codon - detaches from DNA
• mRNA moves out of nucleus through nuclear pores

Question 17

Where does translation take place?

Answer 17

Cytoplasm

Question 18

Explain the process of translation - 11

Answer 18

• Ribosome binds onto mRNA at a start codon
• tRNA molecules carry amino acids to ribosome
• Codon is matched to anticodon by complementary base pairing
• Ribosome holds tRNA in place
• Amino acids joined together by peptide bond
• tRNA molecule moves away leaving amino acid behind
• Ribosome moves to next codon
• Used tRNA has the same amino acid reattached using ATP
• Process continues in producing chain of amino acid [polypetide]
• Ribosome reaches stop codon and moves away from polypeptide chain
• Protein is formed