Unit 1 Topic 5 - Gene Expression And Protein Synthesis

Question 1

Explain the term “genotype”

Answer 1

Genotype is the genes present in an organism

Question 2

Explain the term “phenotype”

Answer 2

Phenotype is the appearance of a characteristic

Question 3

Explain the term “Gene Expression”

Answer 3

Gene Expression is when genes are switched on to produce proteins

Question 4

List the 4 differences between DNA and RNA

Answer 4

DNA
- Found in the nucleus
- double Stranded
- Deoxyribose sugar
- Thymine (T)

RNA
- Found in the nucleus and cytoplasm
- Single stranded
- Ribose Sugar
- Uracil (U)

Question 5

Describe the function of the 3 types of RNA

Answer 5

mRNA - Messenger RNA - Nucleus & Cytoplasm - Carries a copy of the DNA code from nucleus to ribosome.

tRNA - transfer RNA - Cytoplasm and ribosome - Carries amino acids from cytoplasm to ribosome

rRNA - Ribosomal RNA - Ribosomes - Forms part of the structure of Ribosomes

Question 6

Describe the process of transcription to produce the primary mRNA transcript.

Answer 6

1. The enzyme RNA Polymerase unwinds and unzips the double helix
2. Free Nucleotides line up with their complementary DNA Nucleotide.
3. RNA Polymerase adds the RNA nucleotides onto the 3’ end of the growing mRNA strand.
4. This creates a strand of mRNA called the primary transcript.

Question 7

Describe the process of RNA splicing to produce the mature mRNA transcript.

Answer 7

The primary transcript consists of regions called introns and exons.
- The introns are non-coding regions that are removed from the primary transcript.
- the exons are coding regions that code for protein - they are joined together (spliced) to form a mature transcript.
This process is called RNA Splicing.
- the mature transcript then heads out of the nucleus into the cytoplasm and onto the ribosomes.

Question 8

State that Ribosomes are composed of rRNA and protein.

Question 9

State that a triplet of bases on mRNA is called a codon

Question 10

Describe the structure of tRNA

Answer 10

tRNA of exposed bases called an anticodon
An attachment site for a specific amino acid at the 3’ end

Question 11

Describe the steps involved in translation.

Answer 11

1. The mRNA attaches to a ribosome
2. The Ribosome moves along the mRNA until it reaches the mRNA start codon
3. tRNA with the appropriate anticodon attaches to it’s complementary mRNA codon.
4. Amino acids are then linked up by peptide bonds to form a polypeptide chain.
5. Amino acids are added to the chain until the ribosome reaches the mRNA STOP codon.
6. The polypeptide chain then detaches from the Ribosome.

Question 12

Explain how alternative RNA splicing can allow a gene to code for more than one protein.

Answer 12

Living organisms contain less genes than the number of proteins that are produced by their cells.