Topic 4 : Protein synthesis, Mutations, Meosis, Natural selection, Taxonomy and Diversity

Question 1

What is a gene ?

Answer 1

the sequence of DNA bases that codes for the specific amino acid sequence of a polypeptide

Question 2

What is an allele ?

Answer 2

a version of a gene that codes for a different type of the same characteristic

Question 3

What is the genetic code ?

Answer 3

the order of bases in DNA that code for amino acids

Question 4

What are the 3 qualities of the genetic code ?

Answer 4

• degenerate
• non-overlapping
• universal

Question 5

How is the genetic code degenerate ?

Answer 5

different base triplets code for the same amino acid

Question 6

How is the genetic code non-overlapping ?

Answer 6

each base os only read once as part of a triplet

Question 7

How is the genetic code universal ?

Answer 7

the same base triplets all code for the same amino acids in all organisms

Question 8

What are stop codons ?

Answer 8

base triplets that don’t code for an amino acid but for the end of a specific polypeptide

Question 9

What are introns ?

Answer 9

base triplets that do not code for amino acids

Question 10

What are exons ?

Answer 10

base triplets that do code for amino acids

Question 11

What is the genome ?

Answer 11

the complete set of genes and non-coding DNA in a cell

Question 12

What os he proteome ?

Answer 12

the full range of proteins that a cell is able to produce

Question 13

What is transcription ?

Answer 13

the rewriting of part of the DNA code into mRNA

Question 14

Describe the process of transcription.

Answer 14

• DNA uncoils as hydrogen bonds between bases are broken
• one strand acts as a template
• individual RNA nucleotides line up along the DNA nucleotide bases on the template strand according to complementary base pairing
• uracil lines up with adenine
• the sequence of bases in the mRNA is the same as in the non-template strand, except uracil replaces thymine
• individual RNA nucleotides are joined together by RNA polymerase to form a strand of pre-mRNA
• the strand of pre-mRNA leaves the nucleus through the nuclear pore

Question 15

What happens between transcription and translation in protein synthesis ?

Answer 15

splicing of pre-mRNA

Question 16

Describe the process of spring of pre-mRNA.

Answer 16

introns are removed from the pre-mRNA and the exons joined together to form a strand of mRNA

Question 17

Describe the process of translation.

Answer 17

• mRNA attaches to ribosome
• specific tRNA molecules bring their specific amino acids to the ribosome
• the anticodon on the tRNA is complementary to the codon on the mRNA
• peptide bond forms between amino acids
• tRNA detaches to collect another amino acid
• ribosome moves along mRNA until all the codons have been read or a stop codon is reached

Question 18

Describe how a protein forms after translation.

Answer 18

• the polypeptide detaches from the ribosome
• it folds itself into its secondary and tertiary structure by forming hydrogen and ionic bonds which positions are determined by amino acids

Question 19

What are gene mutations ?

Answer 19

changes in the sequence of nucleotide bases in the DNA

Question 20

How and when do mutations occur ?

Answer 20

spontaneously in DNA replication

Question 21

How is the mutation rate increased ?

Answer 21

by mutagenic agents e.g X-rays, benzene

Question 22

What are the types of gene mutation ?

Answer 22

• substitution
• deletion

Question 23

What is substitution ?

Answer 23

the replacement of one or more bases by one or more different bases

Question 24

What might substitution of a single base result in ?

Answer 24

• a new triplet coding for a different amino acid which could result in a non-functional protein being formed
• one different amino acid in the polypeptide changes but a functional protein is formed
• the same amino acid is formed due to degeneracy of genetic code

Question 25

What is deletion ?

Answer 25

removal of one or more bases

Question 26

What does deletion of a base result in ?

Answer 26

- a frame shift which alters the base triplets from the point of deletion - the sequence of amino acids is altered from the point of deletion and so a non-functional protein is almost always formed

Question 27

What is genetic diversity ?

Answer 27

the number of different alleles of genes in a population

Question 28

What increases the genetic diversity of a population ?

Answer 28

the number of different alleles in the population

Question 29

What is adaptation ?

Answer 29

the process by which organisms adjust to suit changes in their environment

Question 30

What are the three types of adaptation ?

Answer 30

- structural - physiological - behavioural

Question 31

How does natural selection occur in the evolution of organisms ?

Answer 31

- variation is present in a population due to random mutations leading to new alleles - the new allele may be advantageous to the organism and so it can reproduce and pass on the allele - a change in the environment can lead to the advantageous allele being selected for as the organism is better adapted - organisms with the allele survive and reproduce and pass on the advantageous allele - over many generations the frequency of the allele increases

Question 32

What is stabilising selection ?

Answer 32

occurs when the environment isn't changing

Question 33

How does stabilising selection occur ?

Answer 33

- natural selection favours the organisms with alleles for characteristics towards the middle of the range - organisms at the extremes of the range are less likely to survive and breed so are less likely to pass their alleles onto the next generation - therefore a similar range of the characteristic is maintained over generations

Question 34

What is directional selection ?

Answer 34

occurs when the environment is changing

Question 35

How does directional selection occur ?

Answer 35

- the change in environment selects for those organisms with alleles for a phenotype towards the extreme of the range - these organisms are more likely to survive and breed, passing on the advantageous allele - the frequency of these alleles increases until an optimum is established

Question 36

What is a species ?

Answer 36

a group of similar organisms that are able to reproduce and give fertile offspring

Question 37

What is taxonomy ?

Answer 37

the science of classification

Question 38

What does taxonomy involve ?

Answer 38

naming organisms and putting them into groups

Question 39

What is a hierarchy ?

Answer 39

smaller groups are placed within larger groups with no overlap between the groups

Question 40

What is the order of classification ?

Answer 40

D - domain K - kingdom P - phylum C - class O - order F - family G - genus S - species

Question 41

How is each species universally identified ?

Answer 41

by a binomial, consisting of the name of its genus (capital letter) and species (lower case)

Question 42

What does courtship enable organisms to do to produce fertile offspring ?

Answer 42

- recognise members of their own species - recognise species of the opposite sex - identify a mate who is capable of breeding - synchronise mating so there is the max probability of the sperm and egg meeting - form a pair bond that will lead to successful mating and raising fertile offspring

Question 43

How does courtship behaviour show how closely related different species are ?

Answer 43

the more closely related the species are, the more similar their courtship behaviour will be

Question 44

How does courtship behaviour work in a stimulus-response chain ?

Answer 44

- the male carries out a specific action which acts as a stimulus for the female to respond to - if the response is correct then courtship continues, if she is not receptive or she is from a different species then her response will be incorrect then the male stops the courtship