OCR A BIOLOGY

Which factors affect evolution?

Mutation, natural selection, sexual selection, gene flow and genetic drift

What is a mutation?

Change in the sequence of bases in DNA

What are the three ways the base sequence can be altered?

Substitution, deletion and insertion

What is the term for a mutation where only one nucleotide is affected?

Point mutation

If a mutation leads to a new codon, what property of the genetic code may mean the protein's primary structure is unaffected?

Degenerate

What type of mutation can be caused by the insertion or deletion of nucleotides?

Frameshift mutation

Which codons does a frameshift mutation affect?

Every successive codon

What is a mutagen?

Chemical, physical or biological agent that causes mutations

What type of mutagen are x-rays?

Physical

What type of mutagen are deaminating agents?

Chemical

What type of mutagen are viruses?

Biological

How do x-rays cause mutations?

Break one or both DNA strands

How do viruses cause mutations?

Viral DNA could insert itself into a genome to change the base sequence

What do nonsense mutations do?

Make a stop codon where there shouldn't be one

What do missense mutations do?

Result in the formation of the wrong amino acid

When is heterochromatin present?

Cell division

When is euchromatin present?

Interphase

Why does transcription not happen during cell division?

Heterochromatin is too tightly wound for RNA polymerase to access the genes

What are epigenetics?

Regulating genes by modifying DNA

What happens if histones become less positive?

DNA coils less tightly which increases transcription

What happens if histones become more hydrophobic?

DNA coils more tightly which prevents transcription

What can be added to histones to make them more hydrophobic?

Methyl groups

What is an operon?

A group of genes under the control of the same regulatory mechanism and are expressed at the same time

Which type of organism has more operons?

Prokaryotic

What are the genes in the lac operon?

LacZ, lacY and lacA

What do the genes in the lac operon code for?

Enzymes

What is the regulatory genes for the lac operon?

LacI

What does LacI code for?

Repressor protein

How does a repressor protein affect the lac operon?

Prevents their transcription in the absence of lactose

What does a repressor protein bind?

Operator

How does a repressor protein prevent transcription?

Prevents RNA polymerase binding to DNA

What is the promoter?

The section of DNA where RNA polymerase binds

How does lactose affect the repressor protein in the case of the lac operon?

Changes its shape so it cannot bind to the operator

Why is glucose still preferred over lactose as a respiratory substrate when they are both present?

Glucose takes less energy to metabolise.

cAMP levels decrease in the presence of glucose which reduces the transcription rate of the lac operon

What is the role of cAMP with regards to the lac operon?

Increase the rate of transcription

What is the product of transcription?

Pre-mRNA

What are introns?

Non-coding DNA

What are extrons?

Coding DNA

What happens when RNA is spliced?

Introns are removed and the extrons joined together

How does the degradation of mRNA regulate protein synthesis?

The more resistant, the longer it lasts, the more proteins are made

How do inhibitory proteins regulate protein synthesis?

Bind to mRNA to stop it binding to ribosomes

What are protein kinases?

Enzymes that catalyse the addition of phosphate groups to proteins

How do protein kinases regulate cell activity?

Change tertiary structure of proteins

What are protein kinases usually activated by?

cAMP

What is post-translational control?

Modifications to proteins

What is morphogenesis?

The regulation of the pattern of anatomical development

What is the purpose of a homeodomain?

Switch other genes on or off

What is a homeodomain?

Part of a protein, highly conserved in plants, animals and fungi

What do homeobox genes code for?

Homeodomain

How many base pairs are in a homeobox?

180

How many amino acids are in a homeodomain?

60

Where are hox genes present?

Animals

How many hox genes do human beings have in total?

39

What is radial symmetry?

When an animal has no right or left sides, only a top and bottom

Give an example of an organism with radial symmetry.

Jellyfish

What is bilateral symmetry?

When organisms have left and right sides as well as a top and bottom

Give an example of an organism with bilateral symmetry.

Humans

Give an example of an organism with asymmetry?

Sponge

What is apoptosis?

Programmed cell death

What is chlorosis?

When leaves don't produce a lot of chlorophyll

Why does an absence of light cause chlorosis?

Leaves stop chlorophyll production to conserve resources

Why does iron deficiency cause chlorosis?

It is needed as a cofactor by some enzymes that make chlorophyll

Why does magnesium deficiency cause chlorosis?

It is part of the chlorophyll molecule

How do viruses cause chlorosis?

Interfere with metabolism and the cells can't support chlorophyll synthesis

What is genotype?

Combination of alleles an organism inherits

What is phenotype?

Observable characteristics in an organism. Depends on genotype and phenotype

Which type of variation is most often caused by just genetics?

Discontinuous

What is monohybrid (or monogenic) inheritance?

The inheritance of a single gene

What is it called when two equally dominant alleles occur for a gene, and are both expressed?

Codominance

How does natural cloning occur in plant bulbs?

Buds form internally and develop into new shoots and new plants in the next growing season

How does natural cloning occur in plant runners?

The lateral stem grows away from the plant and roots develop where it touches the ground, eventually, the runner withers away leaving a new individual

What is a plant rhizome?

A specialised horizontal stem running underground

How does natural cloning occur in plant rhizomes?

Buds develop and form vertical shoots which become independent plants

Which 6 precautions increase the success rate of cloning via plant cuttings?

Use a non-flowering stem, make an oblique cut, use hormone rooting powder, reduce leaves to two or four, water the cutting well, cover with a plastic bag

What is micropropagation?

The process of making large numbers of genetically identical offspring from a single parent plant

What is a callus?

A mass of identical plant cells

What is the disadvantage of having a monoculture?

All the plants are susceptible to the same diseases and changes in conditions

What is a monoculture?

Many plants that are genetically identical

What is the main form of natural vertebrate cloning?

Identical twins

How do identical twins form?

The early embryo splits to form two separate embryos

Which method of artificial animal cloning clones an embryo?

Artificial twinning

Which method of artificial animal cloning clones an adult?

Somatic cell nuclear transfer

What is an enucleated egg cell?

An oocyte with the nucleus removed

How was Dolly cloned?

Somatic cell nuclear transfer

What is a somatic cell?

Body cell

How many adult animals are involved in somatic cell nuclear transfer?

3

Why is cloning animals useful?

More offspring produced, passing on desirable characteristics

How could animal cloning be useful in the future?

Reproducing extinct animals

What are some arguments against animal cloning?

Inefficient, many are miscarried or die young

Why are microorganisms good for use in industry?

No welfare issues, can be genetically engineered, rapid growth rate, few nutrient requirements, processes are cheap to run

What microorganism is involved with baking?

Yeast

Why is yeast good for baking?

Produces carbon dioxide to make bread rise

What microorganism is used in brewing?

Yeast

What microorganism is used in cheese making?

Bacteria

What microorganism is used in yoghurt making?

Bacteria

What are some advantages of using microorganisms to produce food?

Produce protein quickly, high protein content, genetic modification, not dependent on weather, no welfare issues

What are some disadvantages of using microorganisms to produce food?

Can produce toxins, sterile conditions, people don't like eating genetically modified food, needs additives

Why does the process of producing penicillin use relatively small fermenters?

It is difficult to maintain high levels of oxygenation in large bioreactors

What is bioremediation?

The use of microorganisms to break down pollutants in soil or water