Topic 4 - Genetic Information, Variation + Relationships

Question 1

Describe how DNA is arranged in
prokaryotes

Answer 1

In prokaryotic cells, DNA molecules are short, circular and not associated with proteins.

Question 2

Describe how DNA is arranged in
eukaryotes

Answer 2

In the nucleus of eukaryotic cells, DNA molecules are very long, linear and associated with proteins, called histones.

Question 3

Name the organelles (other than the
nucleus) which contain DNA and describe how it is arranged there.

Answer 3

The mitochondria and chloroplasts of eukaryotic cells also contain DNA which, like the DNA of prokaryotes, is short, circular and not associated with protein.

Question 4

What is a chromosome?

Answer 4

DNA molecule and its associated proteins.

Question 5

What is a gene and what does it code for?
(x2)

Answer 5

A gene is a base sequence of DNA that codes for:
1. The amino acid sequence of a polypeptide.
2. A functional RNA (including ribosomal RNA and tRNAs).

Question 6

What is a locus?

Answer 6

The position a gene occupies on a particular DNA molecule.

Question 7

What is a triplet and what does it code for?

Answer 7

A sequence of three DNA bases which codes for a specific amino acid.

Question 8

What is meant by saying that the genetic code is universal?

Answer 8

The same base triplets code for the
same amino acids in all organisms (with some exceptions).

Question 9

What is meant by saying that the genetic code is non-overlapping?

Answer 9

Each base is only read once as part of a specific triplet.

Question 10

What is meant by saying that the genetic code is degenerate?

Answer 10

Differenct base triplets or codons coding for the same amino acid.

Question 11

What is an exon?

Answer 11

Sequences of DNA bases in a gene code for amino acid sequences.

Question 12

What is an intron?

Answer 12

Non-coding sequences of DNA bases in a gene (i.e. do not code for amino acid sequences).

Question 13

What is the genome?

Answer 13

The complete set of genes in a cell.

Question 14

What is the proteome?

Answer 14

The full range of proteins that a cell is able to produce.

Question 15

Describe 4 similarities between mRNA
and tRNA

Answer 15

1. Both polymers of nucleotides / polynucleotide strands.
2. Both nucleotides contain phosphate and ribose.
3. Both contain adenine, uracil, cytosine and guanine bases.
4. Both contain phosphodiester bonds.

Question 16

Describe 4 differences between mRNA
and tRNA

Answer 16

1. mRNA has a linear shape, tRNA has a clover leaf shape.
2. mRNA has no hydrogen bonds, tRNA has hydrogen bonds.
3. mRNA is variable in length, tRNA is not variable in length.
4. mRNA has no amino acid binding site, tRNA does have an amino acid binding site.

Question 17

What are the 2 stages in protein synthesis?

Answer 17

Transcription and translation.

Question 18

Where does transcription occur?

Answer 18

Nucleus.

Question 19

What does transcription in prokaryotes result in?

Answer 19

Results directly in the production of mRNA from DNA.

Question 20

What does transcription in eukaryotes result in?

Answer 20

Results in the production of pre-mRNA; this is then spliced to form mRNA.

Question 21

What occurs in the 1st stage of transcription in eukaryotes?

Answer 21

Hydrogen bonds between DNA bases break.

Question 22

What occurs in the 2nd stage of transcription in eukaryotes after hydrogen bonds are broken?

Answer 22

One DNA strand acts as a template; free RNA nucleotides align by complementary base pairing. In RNA, uracil base pairs with adenine on DNA OR In RNA, uracil is used in place of thymine.

Question 23

What occurs in the 3rd stage of transcription in eukaryotes after bases pair up?

Answer 23

RNA polymerase joins adjacent RNA nucleotides by phosphodiester bonds.

Question 24

What occurs in the 4th stage of transcription in eukaryotes after RNA nucleotides join together?

Answer 24

Pre-mRNA is spliced (introns are removed) to form mRNA.

Question 25

What is the role of RNA polymerase?

Answer 25

Joins adjacent RNA nucleotides with phosphodiester bonds to form pre-mRNA.

Question 26

What occurs in the 1st stage of translation in eukaryotes?

Answer 26

THe mRNA attaches to ribosomes.

Question 27

What occurs in the 2nd stage of translation in eukaryotes after ribsomes attach?

Answer 27

The tRNA anticodons (which bring a specific amino acid) bind to complementary mRNA codon.

Question 28

What occurs in the 3rd stage of translation in eukaryotes after anticodons bind to codons?

Answer 28

Amino acids join by peptide bonds with the use of ATP.

Question 29

What occurs in the 4th stage of translation in eukaryotes after amino acids join together?

Answer 29

The tRNA is released and the ribosome moves along the mRNA to form the polypeptide.

Question 30

What is a gene mutation?

Answer 30

A change in the DNA base sequence of chromosomes.

Question 31

What is a deletion mutation?

Answer 31

The removal of one or more bases.

Question 32

What is a substitution mutation?

Answer 32

The replacement of one or more bases by one or more different bases.

Question 33

What is a mutagenic agent and what do they do?

Answer 33

Mutagenic agents can increase the rate of gene mutation.

Question 34

Name 5 examples of mutagenic agents

Answer 34

X-rays Gamma rays UV light Benzene Alpha and beta particles

Question 35

Why might a substitution not cause a change in the sequence of encoded amino acids?

Answer 35

The genetic code is degenerate – more than one base triplet could code for the same amino acid (CGA and CGG both code for alanine so the polypeptide remains unchanged).

Question 36

What is meant by genetic diversity?

Answer 36

Number of different alleles of genes in a population.

Question 37

Why is variation present in a population?

Answer 37

Random mutations resulting in new alleles of a gene.

Question 38

What happens to the reproductive success of an organism with a beneficial allele?

Answer 38

Increases.

Question 39

What is directional selection – include an example

Answer 39

This occurs when the environment is changing, which selects for those organisms with alleles for a phenotype towards one extreme of a range (e.g antibiotic resistance in bacteria).

Question 40

What is stabilising selection – include an example

Answer 40

This occurs when the environment is not changing (stable). Organisms with alleles for characteristics towards the middle of the range survive to reproduce and pass on their alleles to the next generation (e.g human birth weights).

Question 41

What is a species?

Answer 41

Organisms with similar characteristics which can interbreed to produce fertile offspring.

Question 42

What is courtship behaviour and why is it necessary? (6)

Answer 42

1. Courtship behaviour is a necessary precursor to successful mating Allows organisms to: 2. Recognise members of their own species 3. Recognise members of the opposite sex 4. Identify a mate who is capable of breeding (i.e. sexually mature, fertile and biologically fit) 5. Synchronise mating so that it takes when there is maximum probability of the sperm and egg meeting 6. Form a pair bond that will lead to successful mating and raising of offspring

Question 43

What is phylogenetic classification? Include an explanation of the term hierarchy and taxon (2)

Answer 43

1. Hierarchy – where smaller groups are placed within larger groups, with no overlap between groups 2. Each group a species is put into is called a taxon (plural taxa)

Question 44

List the taxa in order starting with the largest (8)

Answer 44

Domain, kingdom, phylum, class, order, family, genus and species

Question 45

What is binomial naming?

Answer 45

A name which includes genus and species e.g. Homo sapiens

Question 46

What is species richness?

Answer 46

A measure of the number of different species in a community

Question 47

What does index of diversity describe?

Answer 47

Describes the relationship between the number of species in a community and the number of individuals in each species

Question 48

What is the formula for calculating index of diversity?

Answer 48

d = N(N-1) ———— Sum n(n-1)

Question 49

What effect do farming techniques have on biodiversity? Include examples (5)

Answer 49

Farming techniques reduce biodiversity. Examples: Ploughing Grazing Deforestation Pesticides

Question 50

List 4 things which can be compared to measure genetic diversity within or between species

Answer 50

1. The frequency of measurable or observable characteristics 2. The base sequence of DNA 3. The base sequence of mRNA 4. The amino acid sequence of the proteins encoded by DNA and mRNA

Question 51

What is non-disjunction of chromosomes and when might it occur? (3)

Answer 51

1. During meiosis 2. This occurs when a homologous pair of chromosomes do not separate during the first meiotic division 3. Non-disjunction can also occur if the chromatids do not separate in the second meiotic division

Question 52

What is the purpose of meiosis?

Answer 52

Produces haploid daughter cells that are genetically different from each other

Question 53

Explain haploid and diploid cells

Answer 53

1. Haploid cells contain a single set of chromosomes (n) which is half the number of chromosomes in a diploid 2. Diploid cells contain 2 complete cells of chromosomes (2n)

Question 54

Explain how variation occurs due to crossing-over (3)

Answer 54

1. Homologous pair of chromosomes form a bivalent structure 2. Chromatids intertwine, break off and are exchanged 3. Results in the exchange of alleles and can result in new combinations of alleles (recombinants)

Question 55

Describe how variation occurs due to independent segregation (3)

Answer 55

1. Homologous pairs of chromosomes line up on spindle fibres at the equator 2, Each pair lines up independently to the other 3. Therefore, the gametes can contain varied combinations of maternal and paternal chromosomes and alleles

Question 56

Explain how variation occurs due to crossing-over (3)

Answer 56

1. Homologous pair of chromosomes form a bivalent structure 2. Chromatids intertwine, break off and are exchanged 3. Results in the exchange of alleles and can result in new combinations of alleles (recombinants)