3.4.2 DNA and Protein Synthesis

Question 1

Genome

Answer 1

• The complete set of genes in a cell
• Including those in mitochondria and chloroplasts

Question 2

Proteome

Answer 2

The full range of proteins that a cell is able to produce by the genome

Question 3

Complete proteome

Answer 3

Refers to the proteins produced by a given type of cell under a certain set of conditions

Question 4

Structure of RNA

Answer 4

• Polymer made up of repeating mononucleotide sub-units
• Single-stranded
• Pentose sugar: ribose
• Phosphate group
• Organic base (with uracil)

Question 5

Types of RNA that are important in protein synthesis

Answer 5

• messenger RNA (mRNA)
• transfer RNA (tRNA)

Question 6

Structure of mRNA

Answer 6

• Single-stranded
• The base sequence is determined by the sequence of bases in the DNA in transcription
• once formed mRNA leaves the nucleus through the nuclear pore + enters the cytoplasm
• Then it associated with the ribosome and template for protein synthesis

Question 7

Adaptation of mRNA

Answer 7

Possesses information in the form of codons

Question 8

Structure of tRNA

Answer 8

• Small molecule made up of 80 nucleotides
• Single-stranded
• Clover shaped
• Has an anticodon
• Specific to one amino acid

Question 9

Anticodon

Answer 9

• On the tRNA molecule, sequence of 3 other organic bases
• Specific to one amino acid

Question 10

Proteins

Answer 10

• Made up of 1 or more polypeptide chains

Question 11

Stages of polypeptide synthesis

Answer 11

• Transcription (including splicing)
• Translation

Question 12

Polypeptide synthesis: Transcription

Answer 12

Process of making pre-mRNA using a part of DNA as a template

Question 13

Stages of Transcription

Answer 13

• DNA helicase acts on a specific region of the DNA causing the 2 strands to separate and expose the nucleotide bases in that region
• The nucleotide bases on one of the two DNA strands (template strand), pair with their complementary nucleotides from the pool which is present in the nucleus
• RNA polymerase moves along the strand and joins the nucleotides together until a ‘stop’ triplet code is recognised. a pre mRNA molecule is formed

Question 14

Polypeptide synthesis: Splicing (only eukaryotic cells)

Answer 14

• pre mRNA is spliced to form mRNA
• Removal of introns
• mRNA formed leaves through a nuclear pore and is attracted to ribosomes

Question 15

Polypeptide synthesis: Translation

Answer 15

How the final polypeptide is formed

Question 16

Stages of Translation

Answer 16

1. A ribosome attaches to the starting codon (AUG) at one end of the mRNA molecule
2. The tRNA molecule with the complimentary anticodon base sequence (UAC) moves to the ribosome and pairs with the codon on the mRNA
3. The tRNA molecule has a specific amino acid (methionine)
4. Another tRNA molecule with a complimentary anticodon pairs with the next codon
5. A peptide bond forms between the 2 amino acids. An enzyme and ATP which. is hydrolysed is required
6. The tRNA molecules are slowly released so that they can collect another amino acid, and the process repeats until a ‘stop’ codon is reached.
7. A polypeptide chain is formed.

Question 17

Stages of assembling a protein

Answer 17

• The polypeptide chain is coiled or folded -> to produce its secondary structure
• The secondary structure is folded -> to produce its tertiary structure
• Different polypeptide chains and non-protein groups are linked -> to produce the quaternary structure

Question 18

Transcription converts…

Answer 18

mRNA -> DNA