Chapter 8 - DNA, Genes And Protein Syntheis

Question 1

List the differences between prokaryotic DNA and eukaryotic DNA. [3]

Answer 1

Prokaryotic DNA: Circular, not associated with histone proteins, short

Eukaryotic DNA: Linear, associated with histone proteins, long

• also the same for the DNA of mitochondria and chloroplasts.

Question 2

What is a gene?

Answer 2

A base sequence that codes for:
- The amino acid sequence of a polypeptide
- A functional RNA (ribosomal RNA/ tRNA)

A gene has a fixed position, called a locus, on a DNA molecule.

Question 3

What is the genetic code?

Answer 3

• a sequence of 3 DNA bases (triplet) that codes for a specific amino acid.

Question 4

What are the properties of genetic code?

Answer 4

1. Universal - found in all species - provides evidence of evolution
2. Non overlapping - each base is part of only 1 triplet
3. Degenerate - most amino acids are coded for by more than 1 triplet.

Question 5

Why does nuclear DNA in eukaryotes not always code for polypeptides?

Answer 5

Between genes:
. There are non-coding multiple repeats of base sequences

Within a gene:
. Only some bases, called exons, code for amino acid sequences
. These exons are separated by introns which are non coding

Question 6

What is the proteome?

Answer 6

The full range of proteins that a cell can produce

Question 7

What is the genome?

Answer 7

The complete set of genes in a cell

Question 8

What is the role of DNA and RNA?

Answer 8

• THEY ARE IMPORTANT INFO CARRYING MOLECULES.
• DNA holds genetic info and RNA transfers it from DNA to ribosomes during protein synthesis.

Question 9

List the differences between DNA and RNA [4]
Refer to the sugar, bases, strands and length.

Answer 9

DNA:
Sugar - deoxyribose
Bases - thymine, cytosine, guanine, adenine
Strands - double stranded
Length - long

RNA:
Sugar - ribose
Bases - swap thymine for uracil
Strands - single stranded
Length - short

Question 10

What are the 3 uses of RNA?

Answer 10

Ribosomal RNA: makes ribosomes
Messenger RNA(mRNA): protein synthesis
Transfer RNA(tRNA): protein synthesis

Question 11

Protein synthesis 1

Describe the process of transcription.

Answer 11

1. Hydrogen bonds between DNA bases break (catalysed by a helicase enzyme built into RNA polymerase)
2. Only 1 DNA strand acts as a template
3. Free RNA nucleotides align by complementary base pairing
4. In RNA , uracil is used
5. RNA polymerase joins adjacent RNA nucleotides via phosphodiester bonds
6. Pre-mRNA spliced (introns removed) to form mRNA

Question 12

Protein synthesis 2

Describe the process of translation

Answer 12

1. mRNA attaches to ribosome- finds start codon
2. tRNA anticodons bind to complementary mRNA codons
3. tRNA brings a specific amino acid - ribosome can hold 2 tRNA’s at any one time
4. Amino acids join by peptide bonds via a condensation reaction
5. Joining of amino acids requires energy from the hydrolysis of ATP
6. tRNA released after an amino acid is joined to the polypeptide
7. Ribosome moves along mRNA, codon by codon to form the polypeptide.

Question 13

Differences between mRNA and tRNA [5]

Answer 13

mRNA:
1. Linear molecule = no hydrogen bonds or base pairing
2. No amino acid binding site
3. Codons
4. Different lengths
5. More nucleotides

tRNA:
1. Cloverleaf shape
2. Amino acid binding site
3. Anti - codons
4. Similar lengths
5. Less nucleotides

Question 14

Differences in protein synthesis between eukaryotes and prokaryotes [3]

Answer 14

Eukaryotes:
1. DNA has introns so transcription results in pre-mRNA
2. transcription occurs in nucleus
3. translation occurs in cytoplasm

Prokaryotes:
1. No introns so transcription results in mRNA
2/3. All processes in cytoplasm