Protein Synthesis

Question 1

Exons

Answer 1

sections of a gene that code for the sequence of amino acids in a polypeptide

Question 2

Introns

Answer 2

DNA base sequences that do not code for any amino acids in the polypeptide

Question 3

Eukaryotic Vs Prokaryotic DNA

Answer 3

Eukaryotic: linear, associated with histones (proteins), introns

Prokaryotic: circular, not associated with histones, no introns

Question 4

mRNA Vs tRNA

Answer 4

mRNA:
-single stranded
-shorter than DNA
-3 bases=codon
-uracil
-no hydrogen bonds

tRNA:
-single stranded
-about 75 nucleotides
-cloverleaf shape
-held by hydrogen bonds
-3 bases=anticodon

Question 5

function of tRNA

Answer 5

carry a specific amino acid into a ribosome, so protein synthesis can occur

Question 6

Genome definition

Answer 6

complete set of genes in a cell

Question 7

Proteome definition

Answer 7

full range of proteins cell is able to produce

Question 8

Loci definition

Answer 8

position of a gene within chromosome

Question 9

Allele definition

Answer 9

different versions of a gene

Question 10

Gene definition

Answer 10

DNA base sequence that codes for a single polypeptide

Question 11

What does protein synthesis involve?

Answer 11

-Protein synthesis involves the nucleic acids DNA and RNA. -Both are polymers made up by many nucleotides
-joined together by phosphodiester bonds
-through condensation reactions

Question 12

DNA Vs mRNA

Answer 12

DNA:
-double stranded
-longER
-Thymine in DNA
-Deoxyribose in DNA
-has hydrogen bonds
-has introns

mRNA:
-single stranded
-shortER
-Replaced with uracil in RNA
-Ribose in RNA
-doesn’t have hydrogen bonds
-doesn’t have introns

Question 13

Where does transcription occur

Answer 13

prokaryotes- occurs in cytoplasm
eukaryotes- occurs in nucleus

Question 14

Transcription

Answer 14

1. DNA Helicase breaks hydrogen bonds so strands separate;
2. Only one DNA strand acts as template;
3. RNA nucleotides attracted to exposed bases;
4. Attraction according to base pairing rule A-U, C-G, T-A;
5. RNA polymerase joins RNA nucleotides together forming phosphodiester bonds through condensation reactions;
6. Pre-mRNA spliced to remove introns (Eukaryotes).
7. mRNA passes out of nuclear pore into ribosome

Question 15

Where does translation occur?

Answer 15

cytoplasm at a ribosome

Question 16

Translation

Answer 16

1. mRNA attaches to ribosomes
2. tRNA anticodons bind to complementary mRNA codons;
3. tRNA brings a specific amino acid;
4. Amino acids join by peptide bonds;
5. Amino acids join together with the use of ATP;
6. tRNA released after amino acid joined to polypeptide;
7. The ribosome moves along the mRNA to form the polypeptide;

Question 17

The Genetic Code

Answer 17

Universal- the same 3 bases on mRNA / DNA code for the same amino acids in all organisms

Non-overlapping –Each base is only part of 1 triplet / codon

Degenerate- More than one triplet/codon codes for an amino acid
(The first two bases are the most important when coding for amino acids.)

Question 18

What is a gene mutation

Answer 18

A gene mutation is a change to a single base in the DNA base sequence of a gene. These mutations occur randomly and happen spontaneously

Question 19

A mutation in a gene coding for an enzyme
could lead to the production of a non-functional enzyme. Explain how

Answer 19

1. Change in base sequence of DNA
2. Change in amino acid sequence / primary structure
3. Change in hydrogen/ionic/ disulphide bonds;
4. Change in the tertiary structure
5. No enzyme-substrate complexes form;

Question 20

Not all mutations in the nucleotide sequence of a gene cause a change in the structure of a polypeptide. Give two reasons why.

Answer 20

1. Triplets code for same amino acid
2. Occurs in introns /non-coding sequence

Question 21

Substitution Mutations

Answer 21

substitution in third base= silent mutation, mutation does not change the amino acid coded for, so will have no effect on the polypeptide chain (degenerate)

substitution in first/second base= change amino acid sequence, alters sequence of amino acids on the polypeptide chain, so may alter its specific tertiary structure

Question 22

Addition & Deletion Mutations

Answer 22

• frame shift
• different sequence of triplets in DNA
• different primary structure of polypeptide
• different position of R groups
• different tertiary structure

(mutation towards end=lesser effect)

Question 23

How do mutations occur?

Answer 23

occur spontaneously during DNA replication. They are natural, and cause permanent changes to the DNA which is passed on to future generations. They occur at a set rate
-Mutations are responsible for the genetic diversity of populations both in the forces of natural selection and in speciation.
-can be advantageous, disadvantageous or have neutral effects.
-Mutations in gametes can often prove fatal

Question 24

Mutagenic Agents

Answer 24

Mutagenic agents increase the rate of spontaneous mutation

1. High energy ionising radiation (X rays)
2. DNA reactive chemicals such as benzene
3. Biological agents such as some viruses and bacteria.

Question 25

Chromosomal Mutations

Answer 25

-during meiosis the daughter cell produced contains too many chromosome -pair of homologous chromosomes fail to separate in metaphase 1 or sister chromatids fail to separate in metaphase 2 -known as chromosome non-disjunction

Question 26

Inversion Mutations

Answer 26

when a segment of bases is reversed end to end

Question 27

Duplication Mutations

Answer 27

A doubling of a part of a chromosome, of an entire chromosome, or even the whole genome

Question 28

Translocation Mutations

Answer 28

when groups of base pairs relocate from one area of the genome to another, usually between non-homologous chromosomes.

Question 29

What is natural selection?

Answer 29

Process by which organisms that are better adapted to their environment survive and reproduce in greater numbers, resulting in the increase of the frequency of the advantageous allele within the population

Question 30

Explain how selection occurs in living organisms

Answer 30

1. Variation due to mutation; 2. Different selection pressures; 3. Selection for advantageous allele; 4. Selected organisms survive and reproduce; 5. Leads to change in allele frequency; 6. Occurs over a long period of time;

Question 31

Genetic Diversity Definition

Answer 31

the number of different alleles of genes in a population

Question 32

What is phenotype determined by?

Answer 32

the genotype and its interaction with the environment

Question 33

Stabilising Selection

Answer 33

* Occurs in all populations where environment is stable. * Selection pressure at both ends of distribution. * Favours the average. * Tends to eliminate extremes. * Reduces variability * Reduces opportunity for evolutionary change.

Question 34

Directional Selection

Answer 34

* Mean in population represents optimum phenotype for existing conditions * Environmental change may produce new selection pressure that favours an extreme phenotype * Changed conditions, favour allele combination necessary for survival * Some organisms will possess the new optimum phenotype (allele combination) * Over time, selection means this allele combination will predominate and the mean phenotype will shift.

Question 35

Disruptive Selection

Answer 35

* Is the opposite of stabilising selection * Environment has selection pressures that favour 2 extreme phenotypes * When conditions change the optimum phenotypes necessary for survival will also change * Some organisms will possess the new extreme optimum phenotypes * Over time selection means these 2 extremes will dominate and the mean will shift in both directions (towards extremes) * It is the least common type of selection but it is the most important in evolution

Question 36

Dilution Plating Technique

Answer 36

add 1ml of sample into 9ml broth and mix to form 1/10 dilution. add 1ml of 1/10 into fresh 9ml sample broth, mix to form 1/100 dilution...

Question 37

Counting Bacteria Calculations

Answer 37

Counting bacteria after given number of replications: 2^n (n= number of divisions) (if starting amount 100=100x2^n) Finding number of divisions: log2n (n=number of bacteria)

Question 38

How to count bacteria

Answer 38

-counting cells directly -diluting the original sample and then counting cell numbers -turbidity (cloudiness) of the culture with colorimetry

Question 39

Direct cell counts may be divided into

Answer 39

1. Total counts = which include both living cells and dead cells 2. Viable counts = which count living cells only

Question 40

The student looked at cells in a 1 in 10 dilution during his preliminary work. He decided not to use this dilution to determine the number of cells in the undiluted liquid culture. Suggest an explanation for the student’s decision.

Answer 40

1. Count unlikely to be accurate / repeatable / reproducible / reliable; 2. Because too many cells; OR Because cells overlapping / not spread out;

Question 41

Define ‘non-coding base sequences’ and describe where the non-coding multiple repeats are positioned in the genome.

Answer 41

1. DNA that does not code for protein/polypeptides OR DNA that does not code for (sequences of) amino acids OR DNA that does not code for tRNA/rRNA; 2. (Positioned) between genes

Question 42

Define ‘gene mutation’ and explain how a gene mutation can have: * no effect on an individual * a positive effect on an individual.

Answer 42

1. Change in the base sequence of DNA 2. Results in the formation of new allele; (Has no effect because) 3. Genetic code is degenerate (so amino acid sequence may not change); OR Mutation is in an intron (so amino acid sequence may not change); Accept description of ‘degenerate’, eg some amino acids have more than one triplet/codon. (Has positive effect because) 6. Results in change in polypeptide that positively changes the properties (of the protein) 7. May result in increased survival (chances);