Protein Synthesis

Question 1

What is a locus

Answer 1

A gene located in a particular position on dna

Question 2

How many amino acids regularly occur in proteins

Answer 2

20

Question 3

What does degenerate refer to

Answer 3

Most amino acids are coded for by more than 1 triplet

Question 4

What does non overlapping mean

Answer 4

Each base is part of only one triplet

Question 5

What does it mean when the genetic code is universal

Answer 5

Each triplet codes for the same amino acid in all organisms

Question 6

What are exons

Answer 6

Base sequences coding for sequence of amino acids

Question 7

What are introns

Answer 7

Non coding sequences

Question 8

What is the difference between prokaryotic and eukaryotic DNA

Answer 8

In prokaryotic cells, there is no nucleis and the dna molecules are short, circular, contain plasmids and are not associated with proteins. In eukayotic cells there is a nucleus with nuclear envelope and the dna molecule is very long, linear, associated with histones (proteins) and contains no plasmids

Question 9

How is a chromosome formed

Answer 9

Dna molecules, in association with histones, form chromosomes

Question 10

What is significant about the mitchondria and chloroplasts of eukaryotic cells

Answer 10

Contain dna similar to prokaryotes: short, circular and not associated with proteins

Question 11

What is a gene

Answer 11

A base sequence of dna that codes for the amino acid sequence of a polypeptide and functional RNA (including ribsomal rna and trna)

Question 12

Where is a gene located

Answer 12

A gene occupies a fixed position called a locus on a particular dna molecule

Question 13

What are 3 features of the genetic code

Answer 13

Universal, non overlapping and degenerate

Question 14

Much of the nuclear dna in eukaryotes doesn’t what

Answer 14

Code for polypeptides

Question 15

What is a homologuous pair

Answer 15

Two chromosomes that cary the same genes but not the same alleles of the genes

Question 16

What is an allele

Answer 16

One of a number of alternate forms of a gene

Question 17

What is the genome

Answer 17

The complete set of genes in a cell (including those in mitochondria and chloroplasts)

Question 18

What is the proteome

Answer 18

The full range of proteins produced by a cell/ genome

Question 19

What is rna

Answer 19

A single stranded polymer, made up of repeating mononucleotide subunits

Question 20

Describe the structure of an rna nucleotide

Answer 20

Contains the pentose sugar RIBOSE, a phosphate group and one of the organic bases A,C,G or URACIL

Question 21

Describe the structure of mrna

Answer 21

Long, single, linear strand with no hydrogen bonds. Its length and quantitity varies as its base sequence is determined by dna. It also has codons (3 bases complementrary to dna) amd its structure is less stable than trna and dna

Question 22

Describe the structure of trna

Answer 22

Small, single strand folded into clover leaf shape. It contains hydrogen bonds and has an anticodon which is specific to one amino acid. Its length stays the same

Question 23

Describe the process of transcription

Answer 23

1. Dna helicase unwinds and unzips the dna molecule, breaking H bonds and exposing bases on a template strand 2. Free activated rna nucleotides pair with complementary bases 3. Rna polymerase joins nucleotides into strand until stop code is reached 4. Pre mrna detaches and is spliced into mrna by removing introns 5. Mrna leaves nucleus via pore into cytoplasm where it attaches to ribosome

Question 24

What is the difference between prokaryotic and eukaryotic transcription

Answer 24

In prokaryotic cells, transcription directly results in the production of mrna from dna but in eukaryotic cells, transcription produces pre mrna which is spliced (removing introns) to form mrna

Question 25

Describe the process of translation 1-3

Answer 25

1. A ribosome attaches to the start codon on mrna 2. The trna molecule with the complementary anticodon sequence moves to ribosome and pairs with codon on mrna, the trna carries a specific AA 3. A trna molecule with complementary anticodon pairs with next codon on mrna, trna carries another AA

Question 26

Describe the process of translation 4-7

Answer 26

4. The ribosome moves along the mrna, brining together 2 trna molecules at a time 5. The 2 amino acids on trnas are joined by a peptide bond using an enzyme and energy from atp 6. Ribosome moves to 3rd codon, linking AAs on 2nd & 3rd trnas and the 1st is released & free to collect another AA = polypeptide is formed 7. Process continues until ribosome reaches stop code

Question 27

What is a gene mutation

Answer 27

A change in the quantity or base sequnce of dna/ chromosomes

Question 28

Gene mutations can arrise spontanously during dna replication, true or false?

Answer 28

True

Question 29

What types of gene mutations are there

Answer 29

Base substitution and base deletion

Question 30

What happens in substitution of bases

Answer 30

A nucleotide in a dna molecule is replaced with another nucleotide that has a different base

Question 31

What can be the effects of a substitution of bases

Answer 31

The primary structure will differ so a different polypeptide may be produced, means bonds that form tertiary structure may change so the shape of active site may change so its no longer complementary to substrate to form ecs

Question 32

Why do not all base substitutions have an effect

Answer 32

Not all cause a change in the sequence of AAs as the genetic code is degenerate (most AA coded for by more than one base triplet/codon)

Question 33

What problem does base deletion cause

Answer 33

Sequences of dna are read in units of 3 so a deleted nucleotide cause all triplets to be read differently as each has been shifted to the left by one. This can create different polypeptides (won’t function correctly)

Question 34

What is a chromosome mutation

Answer 34

Changes in the structure or number of whole chromosomes

Question 35

What are the two forms of chromosome mutation

Answer 35

1.changes in whole sets of chromosomes, where organisms have 3 or more sets (polyploidy) 2.changes in number of chromosomes, where pairs fail to separate in meiosis (non disjunction) so gamete has 1 more/ less chromosome

Question 36

What are mutagenic agents (give examples)

Answer 36

Exposure to mutagenic agents can increase the rate of mutations, examples are high energy ionising radiation (alpha, beta, gamma radiation) and chemicals like nitrogen dioxide or benzopyrene (in tabacco)

Question 37

What is one advantage of showing the genetic code as base sequences on mRNA rather than dna

Answer 37

As ribosomes assemble polypeptides using the mRNA code. Dna has 2 strands, each with a different complementary base sequence