Topic 4 - DNA, chromosomes etc!

What is a gene

A section of DNA that contains a code for making a polypeptide and functional RNA, the code is a specific sequence of bases.

what is a locus

the location of a particular gene on a chromosome

definition of an allele

An allele is one of a number of alternative forms of a gene. Most genes occur in two occasionally more different forms

draw and label a chromosome

correctly labelled chromosome

What is a homologous pair

A homologous pair of chromosomes are exactly same size they have exactly same genes but might have different alleles

DNA storage in a eukaryote

DNA stored as chromosomes inside of the nucleus. Chromosomes in eukaryotic cells are linear in shape. To tightly coil the DNA to fit in the nucleus the DNA is tightly wound around proteins called histones.

This complex on DNA wrapped around a histone is called a nucleosome.

DNA in prokaryotic cells

Also carry DNA in chromosomes but DNA molecules are shorter and circular, not wound around histones.

Similarities between mitochondria, chloroplast and prokaryotic DNA

short and circular

There are 20 different amino acids the genetic code has to be able to code for. The genetic code is triplet (4³).

As 4³ = 64. 64 combinations is more than needed to code for 20 amino acids meaning each amino acid is coded for by more than one triplet of bases.

Why is the dna being degenerate an advantage

If a point mutation occurs even though the triplet of bases will be different it may still code for the same amino acid and therefore have no effect

How is genetic code universal

The same triplet of bases code for the same amino acid in all organisms

advantage of genetic code being universal

means genetic engineering is possible eg inserting human gene for insulin into bacteria

what does non overlapping mean for genetic code

Each base in a gene is only part of one triplet of bases that codes for one amino acid. Therefore each codon, or triplet of bases is read as a discrete unit

Eg

ACG GCT TCA ACT

Why is the genetic code being non overlapping an advantage

As if a mutation occurs it will only affect one codon and therefore one amino acid

What are introns

Introns are sections of DNA that do not code for amino acids and therefore dont code for polypeptide chains. Introns are found in eukaryotic DNA but not in prokaryotic DNA. They are in mrna but get spliced

What are exons

sections of dna that do code for amino acids

what is genome and proteome

The genome is an organisms complete set of DNA in one cell where as the proteome is the full range of proteins in one cell

what is in RNA nucleotide

ribose, nitrogenous base and phosphate

what are nitrogenous bases in RNA -

adenine, guanine, cytosine and uracil

what is mrna and features

a copy of gene from dna. it is created in nucleus and leaves nucleus to carry the copy of the genetic code of one gene to a ribosome in the cytoplasm. mrna is shorter than dna so can leave the nucleus, but ie short lived as is only required temporarily.

mRNA is single stranded

trna facts and features

found only in the cytoplasm, single stranded but folded to create a cloverleaf like shape which is held in place by hydrogen bonds. contains anticodon which is complementary to codon on mrna

Compare RNA and DNA monomers

DNA contains bade thymine whereas rna contains uracil

DNA contains pentose sugar deoxyribose, whereas RNA contains pentose sugar ribose.

compare DNA and RNA polymers

DNA is much larger whereas rna is much shorter as its only the length of one gene

dna is double stranded whereas rna is single stranded

Describe process of transcription

1. the dna helix unwinds to expose the bases to act as a template, this is catalysed by dna helicase

2. only one chain of dna acts as a template

3. DNA helicase breaks the hydrogen bonds between bases

4. free mrna nucleotides in the nucleus align opposite exposed complementary dna bases.

5. Joins adjacent nucleotides together

6. The enzyme rna polymerase bonds together the rna nucleotides to create a new rna polymer chain. one entire gene is copied.

premrna gets modified to become mrna by splicing. the introns are spliced out by a protein called splicesome. This leaves behind just the exons, coding regions.

describe translation

1. Once modified mrna has left the nucleus attaches to a ribosome in the cytoplasm

2. the ribosome attaches at the start codon

3. the trna molecule with the complementary anticodon to the start codon aligns opposite the mrna held in place by the ribosome.

4. The ribosome moved along the mrna molecule to enable another complementary trna to attach to the next codon on mrna

5. the two amino acids that have been delivered by trna molecule are joined by a peptide bond. this is catalysed by an enzyme and requires atp

6. This continued until ribosome reaches stop coronary at the end of mrna molecule. the stop codon does not code for an amino acids and therefore ribosome detaches and translation ends.

what is meiosis

type of cell division which produces daughter cells which are genetically different from each other.

meiosis involves two nuclear divisions and creates four haploid daughter cells from a single diploid ( two copies of homologous chromosomes ) parent cell.

what occurs in independent segregation / assortment

In meiosis 1, homologous pairs of chromosomes line up opposite eachother at the equator if cell. it is random placement of chromosomes along equator. these pairs are separated so one of each homologous pair ends up in the daughter cell. This creates a larger number of possible combinations in the daughter cells

what happens during crossing over

when homologous pairs line up opposite eachother other at the equator in meiosis 1, parts of the chromatids can become twisted around eachother (point of twist is called chiasmata) this puts tension on the chromatids causing parts of the chromatid to break. The broken parts of the chromatid recombine with another chromatid. resulting in new combinations of alleles

what is non disjunction

when chromosomes or chromatids do not split equally during anaphase

what is polploidy

changes in while sets of chromosomes occur when organisms have 3 or more sets of chromosomes rather than the usual two. normally occurs in plants

what js aneuploidy

individual homologous pairs of chromosomes fail to separate during meiosis. resulting in a gamete having one more or one fewer chromosome

what is genetic diversify

the number of different alleles of genes in a population

What is natural selection

Process which leads to evolution in populations, evolution is the change in allele frequency over many generations in a population. Natural selection results in species becoming better adapted to their encironment.

types of adaptations

anatomical - structural features eg shape of a beak of a bird

Physiological - chemical reactions within body eg quantities of chemicals or enzymes

behavioural - how the organism behaves eg penguins huddling together

Describe the Process of natural selection

1. new alleles for a gene created by random mutations

2. if the new alleles increase the chances of the individual to survive in that environment then they are more likely to survive and reproduce

3. this reproduction passes on the advantageous allele to the next generation

4. as a result over many generations the new allele increases in frequency in the population

what is directional selection

one of the extremes has the selective advantage

occurs when there is a change in the environment

the modal trait changes

eg antibiotic resistance in bacteria

what us stabilising selection

The modal traits has the selective advantag

occurs when there is no change in the environment

modal trait remains same

standard deviation decreases as individuals with the extreme trait decrease

eg baby birth weight

what is a species

a group if similar organisms that can breed to produce fertile offspring

what are courtship rituals

sequence of actions which are unique to each species this is how animals identify members of their own species to reproduce with.

what is the importance of courtship rituals

ensures successful reproduction

• enabled them to recognise their own species and opposite sex

• synchronises mating behaviour - indicates sexually mature and in season (releasing egg)

  to ensure survival of offspring

• form a pair bond

• choose a strong and healthy mate

What is the binomial system

first name is genus second name is species

what is a hierarchy (in terms of classification)

smaller groups arranged within larger groups, there is no overlap between groups

modern and accurate classification methods

DNA sequence

mrna sequence

amino acids sequence

immunological - comparing similarities in self- antibody shape

What is phylogenetic classification

Arranging species into groups according to their evolutionary origins and relationships.

what is species diversity

The number of different species and individuals within each species in a community

Species richness definition

the number of different species in a particular area at the particular time

genetic diversity definition

the variety of genes amongst all the individuals in a population of one species

ecosystem diversity

range of different habitats

how does farming reduce biodiversity

1. destruction of hedgerows - as they provide habitats for insects etc

2. selective breeding - reduces gene pool

3. monocultures - only growing one plant species in the entire field

4. overgrazing reducing plants

5. filling in ponds and draining wetland to provide space

how to measure biodiversity

index of diversity - measure if species diversity. it is a calculation to measure relationship between the number of species in a community and the number of individuals in each species.

what is the cell cycle made out of?(in terms of stages )

Interphase (G1, S, G2)

G1- growth

S- DNA synthesis

G2- growth and preparation for mitosis

Interphase is the longest stage in the cell cycle. Interphase is when the organelles double, the cell grows and then DNA replicates.

Nuclear division -can be either mitosis, creating two identical diploid cells, or meiosis, creating four genetically different haploid cells. Mitosis creates cells with identical DNA for growth and repair, where as meiosis creates gametes.

Cytokinesis -the final stage. It is the division of the cytoplasm to create the new cells.

what occurs in prophase

chromosomes condense and become visible. In animal cells, the centrioles separate and move to opposite poles of the cell.

metaphase

The chromosomes align along the equator of cell. The spindle fibres released from the poles now attach to the centromere and chromatid.

anaphase

The spindle fibres start to retract and pull the centromere and chromatids they are bound to towards the opposite poles. This causes the centromere to divide in two and the individual chromatids and pulled to each opposite pole. These separated chromatids and now referred to as chromosomes.

This stage requires energy in the form of ATP which is provided by respiration in the mitochondria.

telophase

The chromosomes are now at each pole of the cell and become longer and thinner again.

The spindle fibres disintegrate, and the nucleus starts to reform.

The final stage in the cell cycle is when the cytoplasm splits in two to create the two new genetically identical cells.