4 Genetic Information: 8 DNA, genes and protein synthesis

Question 1

What is a gene?

Answer 1

A base sequence of DNA that codes for
- the amino acid sequence of a polypeptide
- a functional RNA (including ribosomal RNA and tRNAs)

Question 2

What is a locus?

Answer 2

A fixed position on a particular DNA molecule that a gene occupies.

Question 3

What is a triplet?

Answer 3

A sequence of three DNA bases that codes for a specific amino acid.

Question 4

What features does the genetic code have? What do they mean?

Answer 4

Universal - the same triplet codes for the same amino acid in all organisms
Non-overlapping - each triplet only reads once
Degenerate - one amino acid can be coded for by more than one codon

Question 5

What are exons?

Answer 5

Coding sequences for amino acids.

Question 6

What are introns?

Answer 6

Non-coding sequences within a gene.

Question 7

What are DNA molecules like in prokaryotic cells?

Answer 7

Short, circular, and not associated with proteins.

Question 8

What are DNA molecules like in eukaryotic cells?

Answer 8

Long, linear, and associated with proteins (histones).

Question 9

What are the DNA molecules like in mitochondrion and chloroplasts?

Answer 9

Like prokaryotic DNA, they are also short, circular, and not associated with proteins.

Question 10

What is the genome?

Answer 10

The complete set of genes in a cell.

Question 11

What is the proteome?

Answer 11

The full range of proteins that a cell is able to produce.

Question 12

What is the structure of a molecule of mRNA?

Answer 12

• a single polynucleotide strand with more nucleotides
• has codons
• doesn’t have base pairing/ hydrogen bonding
• doesn’t have an amino acid binding site

Question 13

What is the structure of a molecule of tRNA?

Answer 13

• single polynucleotide that is folded into a clover shape
• has hydrogen bonds between specific base pairs
• has an anticodon
• has an amino acid binding site

Question 14

What is transcription?

Answer 14

The production of mRNA from DNA using RNA polymerase in joining mRNA nucleotides.

Question 15

In prokaryotes, what does transcription result in?

Answer 15

mRNA

Question 16

In eukaryotes, what does transcription result in?

Answer 16

The production of pre-mRNA which is then spliced to form mRNA.

Question 17

What is translation?

Answer 17

The production of polypeptides from the sequence of codons carried by mRNA.

Question 18

What is the process of transcription?

Answer 18

In eukaryotes:
1. DNA helicase breaks the hydrogen bonds between the two DNA strands, uncoiling the double helix to expose some bases.
2. One of the strands is used as a template to make an mRNA copy.
3. The RNA polymerase lines up free RNA nucleotides alongside the exposed bases on the template strand via complementary base pairing. (U instead of T)
4. RNA polymerase joins the RNA nucleotide, forming phosphodiester bonds to form pre-mRNA.
5. The hydrogen bonds reform between the DNA strands.
6. Once the RNA polymerase reaches the stop triplet, it detaches from the DNA.
7. Splicing occurs where introns are removed to leave only the exons, forming mRNA.
8. The mRNA then leaves the nucleus through a nuclear pore.

Question 19

What is the process of translation?

Answer 19

1. The mRNA attaches to a ribosome which moves along the strand.
2. A tRNA molecule (carrying a specific amino acid) with a complementary anticodon attaches to the first codon on the mRNA.
3. A complementary second tRNA molecule does the same.
4. The two amino acids are joined by a peptide bond using ATP.
5. The first tRNA molecule is released and free to collect another amino acid.
6. The process continues until a stop codon is reached which causes the ribosome to detach, leaving a polypeptide chain.