Biology 1.2 Transcription and Translation

Question 1

What is a gene?

Answer 1

A gene is a section of DNA that codes for a specific protein or RNA

Question 2

Introns and Exons

Answer 2

DNA contains both coding sequence and non-coding sequnce. Exons: coding DNA. Introns: non-coding DNA.

Question 3

DNA to Protein

Answer 3

Step 1: Transcription
Step 2: Splicing
Step 3: Translation

Question 4

Steps of Transcription

Answer 4

1. DNA is unzipped at a specific gene
2. RNA polymerase uses free RNA nucleotides to synthesise an RNA copy of the specific gene.
3. The whole gene is copied, including non-coding introns.
4. After copying, the DNA is zipped up again.

Question 5

Transcription

Answer 5

Occurs in the nucleus of eukaryotic cells. The template strand is copied. The RNA produced will be processed to form a mRNA. mRNA takes a copy of the gene code to the cytoplasm.

Question 6

Splicing

Answer 6

After a gene is transcribed from DNA, the non-coding introns must be removed. An RNA enzyme complex called a spliceosome brings exon ends together and cuts out the introns. The final mRNA contains only coding sequences, ready for translation in the cytoplasm.

Question 7

Codons and Amino Acids

Answer 7

A gene is specific sequence of nucleotides in DNA. A group of three nucleotides is a codon. One codon codes for one amino acid. The sequence of codons codes for a specific sequence of amino acids in a polypeptide.

Question 8

Translation

Answer 8

In the cytoplasm, a ribosome assembles around the mRNA. Specific amino acids are carried to the ribosome by transfer RNAs. The anticodon on a tRNA is complementary to a codon on the mRNA. Amino acids are joined to form a polypeptide.

Question 9

3 key step of translation

Answer 9

1. Initiation
2. Elongation
3. Termination

Question 10

Translation - Initiation

Answer 10

All genes start with an AUG codon. The initiator tRNA with a UAC anticodon binds to the mRNA. The ribosome subunits assemble at this location.

Question 11

Translation - Elongation

Answer 11

The next tRNA enters the ribosome, bringing a specific amino acid. A peptide bond forms between the first and second amino acids. The ribosome moves to the next codon, the first tRNA is released and the process repeats.

Question 12

Translation - Termination

Answer 12

Elongation continues until the ribosome reaches a STOP codon. STOP codon do not code for an amino acid. Instead, they recruit a release factor to disassemble the ribosome and release the polypeptide.