Topic 8 - DNA, Genes, and Chromosomes

Question 1

What stage in the cell cycle do chromosomes become visible and take on their X shape?

Answer 1

Prophase.

Question 2

How is DNA arranged within a chromosome?

Answer 2

DNA double helix wound around histones proteins, then coiled, folded, then coiled further before being packed into a chromosome.

Question 3

What is a phenotype?

Answer 3

Combination of proteins interacting with the environment.

Question 4

What is an intron?

Answer 4

Non-coding section of DNA.

Question 5

What is an exon?

Answer 5

Coding section of DNA.

Question 6

What is a gene?

Answer 6

Section of DNA that codes for a polypeptide, found at a particular locus.

Question 7

What is a degenerate code?

Answer 7

All but 2 amino acids have more than 1 DNA triplet.

Question 8

What is a non-overlapping code?

Answer 8

Each triplet only read once.

Question 9

What is a universal code?

Answer 9

The same in (almost) all organisms.

Question 10

What is a (point) mutation?

Answer 10

Has a different DNA nucleotide. Can make a new allele.

Question 11

True or false? The genetic code is degenerate.

Answer 11

True.

Question 12

Is RNA double-stranded or single-stranded?

Answer 12

Single-stranded.

Question 13

How does the quantity in a gamete differs from that in a body cell?

Answer 13

Amount of DNA in gamete is half that in a body cell.

Question 14

Why does DNA need to be chemically stable?

Answer 14

So that it can resist change which could lead to mutations.

Question 15

How does transcription work?

Answer 15

1) DNA helicase unwinds section of DNA to expose gene needed for protein synthesis. Breaks hydrogen bonds between bases in double helix.
2) RNA polymerase attaches to template strand and joins complementary RNA nucleotides together.
3) Forms pre-mRNA.
4) Pre-mRNA spliced to form mRNA.
5) mRNA diffuses out nucleus (through nuclear pores).
6) RNA polymerase detaches, DNA rewinds and forms hydrogen bonds between complementary bases.

Question 16

What are the advantages of a molecule of DNA having both strands even if one is not used?

Answer 16

• Protects genetic code.
• Makes DNA mores stable.
• Semi-conservative replication.

Question 17

Why does transcription in prokaryotic cells produce mRNA rather than pre-mRNA?

Answer 17

Most don’t have introns so splicing of DNA is unnecessary.

Question 18

What are the stages of translation?

Answer 18

1) mRNA molecule associates with a ribosome in cytoplasm.
2) 1st 2 codons attract complementary tRNA molecules.
3) Anticodons of tRNA molecules join via complementary base pairing, forms hydrogen bonds with mRNA codons.
4) Peptide bond formed between 2 amino acids, catalysed by Peptidyl Transferase.
5) Ribosome moves forward by one codon.
6) First tRNA leaves ribosome, new tRNA enters it, carrying amino acid towards 3rd codon.
7) Another peptide bond formed between 2nd amino acid and new one, forms a polypeptide.
8) Ribosome continues moving along mRNA until reaches a stop codon. Will detach.
9) Polypeptide chain is released, folding into correct shape.