DNA, Genes and Chromosomes

Question 1

What are the differences between prokaryotic and eukaryotic genetic material?

Answer 1

• prokaryotic DNA is found in the cytoplasm, eukaryotic DNA is found in the nucleus
• prokaryotic DNA is circular, eukaryotic DNA is linear (chromatin)
• prokaryotic DNA is not associated with proteins, eukaryotic DNA is associated with proteins (histones)
• prokaryotic DNA is smaller, eukaryotic DNA is longer
• prokaryotic DNA does not contain introns, eukaryotic DNA does

Question 2

How is DNA packed into chromosomes?

Answer 2

Hydrogen bonds connect complementary base pairs on opposite strands of DNA, which is wound into a double helix. DNA wraps around proteins called histones to form structures called nucleosomes, which are the basic units of chromatin. Chromatin is what makes up the chromosome

Question 3

What are the similarities and differences between RNA and DNA?

Answer 3

• Both contain a phosphate group, pentose sugar and nitrogenous base
• Both contain adenine, cytosine and guanine
• Both polymers of nucleotides joined by phosphodiester bonds
• DNA is double stranded whereas RNA is single stranded
• DNA has a thymine base whereas RNA has a uracil base
• DNA has a deoxyribose sugar whereas RNA has a ribose sugar

Question 4

Where is DNA found in eukaryotic cells?

Answer 4

DNA is found within chromosomes in the nucleus, however can also be found in structures such as mitochondria and chloroplasts, however like prokaryotic DNA, it is short, circular and not associated with proteins

Question 5

What is a gene?

Answer 5

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

Question 6

What is a locus?

Answer 6

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

Question 7

If the DNA base sequence is TACGGTAAT, what is the mRNA base sequence?

Answer 7

AUGCCAUUA

complementary base pairing rules, except U (rather than A) bonds with T

Question 8

If the mRNA base sequence is AUGCCAUUA, what is the tRNA anticodon?

Answer 8

UACGGUAAU

complementary base pairing rules, except A bonds to U, and U bonds to A

Question 9

If the DNA base sequence is TACGGTAAT, what is the tRNA anticodon?

Answer 9

UACGGUAAU

the bases will stay the same, except for T which is replaced with U

Question 10

Which base sequence codes for the amino acid sequence?

Answer 10

mRNA

Question 11

What 3 words are used to describe the genetic code?

Answer 11

universal, non-overlapping and degenerate

Question 12

What does non-overlapping mean?

Answer 12

Each base is only used once in coding for an amino acid

Question 13

What does universal mean?

Answer 13

The genetic code is identical in all organisms

Question 14

What does degenerate mean?

Answer 14

Some amino acids are represented by more than one codon, eg. GAU and GAC both code for Asp

Question 15

What is a codon?

Answer 15

3 adjacent bases on mRNA that code for an amino acid

Question 16

Why are 3 bases needed to code for each amino acid?

Answer 16

Because at least 20 different codons are needed to code for 20 different amino acids

1 base = 4^1, 4 triplets
2 bases = 4^2, 16 triplets
3 bases = 4^3, 64 triplets - 64>20

Question 17

What is the advantage of a cell having a degenerate code?

Answer 17

It is less likely that a change to the DNA will change the amino acid sequence (silent mutation)

Question 18

What is a sequence of 3 bases called?

Answer 18

triplet

Question 19

Why does much of the nuclear DNA in eukaryotes not code for polypeptides?

Answer 19

• there are non-coding multiple repeats of base sequence between genes
• only some sequences (exons) code for amino acid sequences
• within genes, exons are separated by one or more non-coding sequences called introns

Question 20

What 2 molecules are found within the nucleus?

Answer 20

• DNA
• histones

Question 21

Describe how a gene is a code for the production of a polypeptide

Answer 21

A gene is a base sequence on DNA. The base sequence in the triplet code determines the sequence of amino acids in the production of polypeptides

Question 22

Define exon

Answer 22

Base sequence in DNA that codes for a polypeptide

Question 23

Describe how phosphodiester bonds form between 2 nucleotides

Answer 23

• form in a condensation reaction which releases a molecule of water
• between deoxyribose and phosphate
• catalysed by DNA polymerase

Question 24

Where are non-coding regions positioned in the genome

Answer 24

between genes

Question 25

What is a homologous pair of chromosomes?

Answer 25

2 chromosomes carrying the same genes