Topic 4 Flashcards
Describe how DNA is arranged in prokaryotes
In prokaryotic cells, DNA molecules are short, circular and not associated protein with proteins
Describe how DNA is arranged in eukaryotes
In the nucleus of eukaryotic cells, DNA molecules are very long linear and associated with proteins
Name the organelles, other than the nucleus, that contain DNA and describe how it is arranged here
Me mitochondria and chloroplasts of eukaryotic cells also contain DNA and like prokaryotic DNA it is shout circular and not protein associated
What is a chromosome?
DNA molecule associated with proteins
What is a gene and what doesit code for ( 2x bullet points)?
A gene is a base sequence of DNA that codes for:
- the amino acid sequence of a polypeptide
- a functional RNA (including ribosomal and tRNA)
What is meant by saying the genetic code is universal?
The same base triplets code for the same amino acids in all organisms (with some exceptions)
What is a locus?
The position a gene occupies on a particular DNA molecule.
What is a maple and what does it code for?
A sequence of three DNA bases that code for a specific amino acid
What is meant by saying the genetic code is non-overlapping?
Each base is only read once as apart of a specific triplet
What is meant by saying that the genetic code is degenerate?
Different base triplets /codons coding for the same amino acid
What is an exon?
Coding Sequences of DNA bases in a gene-they code for amino acid sequences
What is an intron?
Non-coding sequences of DNA bases in a gene
What is he genome?
The complete set of genes in a cell
What is a proteome?
The full range of proteins that a cell is able to produce
Describe the similarities between mRNA and tRNA
- Both are polymers of nucleotides/ polynucleotide strands
-nucleotide bases are adenine, uracil, guanine and cytosine - both contain ribose
- mom contain phosphodiester bonds
Describe the differences between mRNA and tRNA
- mRNA has a linear shape tRNA has a clover leaf shape
-mRNA does snot have hydrogen bands tRNA has hydrogen bonds - mRNA is variable in length, tRNA is not
-mRNA does not have an amino acid binding site, tRNA does
What happens in transcription?
1) Hydrogen bonds break
2) Only one DNA strand acts as a template
3) Free RNA nucleotides align based on complementary base pairing
4) In RNA uracil base pairs with adenine on DNA.
5) RNA polymerase joins adjacent nucleotides by phosphodiester bonds
7) Pre-mRNA is spliced removing introns to form mRNA
Where does transcription take place? (Eukaryotes)
In eukaryotes transcription occurs sin the nucleus.
How does transcription dissed eukaryotes and prokaryotes?
In prokaryotes transcription results directly in the production of mRNA from DNA
In eukaryotes transcription results in the production of pre-mRNA which is then spliced to form mRNA
What is the role of RNA polymerase?
Joins adjacent nucleotides with phosphodiester bonds to form pre-mRNA
Where does translocation occur?
The ribosome in the cytoplasm.
Describe translocation
1) mRNA attaches to the rough endoplasmic reticulum of ribosomes
2) tRNA anticodons bind to complementary mRNA codons
3) tRNA brings a specific amino acid
4) Amino acids join by condensation reactions forming peptide bonds
5) They use ATP to join together
6) tRNA is released after the amino acid has joined to the polypeptide
7) The ribosome moves along the mRNA to form the polypeptide
What is a gene mutation?
Gene mutations involve a change in the DNA base sequence of chromosomes
What is deletion?
The removal of one or more bases leading to a frame shift.
What is substitution?
The replacement of one or more bases by one or more different bases
What is a mutagenic agent and what do they do? Give some examples
Mutagenic agents can increase the rate of gene mutation.
EXAMPLES INCLUDE:
- benzene
- x rays
- gamma rays
- UV light
- alpha and beta particles
Why might a substitution not cause a change in the sequence of encoded amino acids?
The genetic code is degenerate meaning more than one base triplet could code for the same amino acid
What is non-disjunction of chromosomes and when might it occur?
The homologous pair of chromosomes do not separate during the first meiotic division.
It can also occur if the chromatids do not separate in the second meiotic division.
It might occur during meiosis
What is the purpose of meiosis?
Meiosis produces haploid daughter cells that are genetically different from each other
Explain the term haploid
A haploid cell contains a single set of chromosomes. (n)
Half the number of chromosomes in a diploid cell
Explain the term diploid
A cell that contains two complete sets of chromosomes (2n)
Describe how variation occurs due to crossing over
- Homologous pair of chromosomes form a structure known as a bivalent
- Chromatids intertwine, break of and a exchanged.
- Resulting in an exchange of alleles and can result in new combinations of alleles known as recombinants
Describe how variation occurs due to independent segregation
- The homologous pairs of chromosomes line up on spindle fibres at the equator, each pairs lines up independently to the other
- The subsequent separation of the two members of a pair is completely independent from the separation of another pair during anaphase
- The gametes can contain varied combinations of maternal and paternal chromosomes and alleles.
What do we mean by genetic diversity?
Genertic diversity is the number of different alleles of a gene within a population
What are the principles of natural selection?
- Variation will already be present in the population due to random mutations which can result in new alleles of genes.
- Many mutations are harmful but in certain environments the new allele of a gene might benefit an organism leading to increased reproductive success
- A change in the environment results in organisms with advantageous alleles for a particular phenotype being selected for as they are better adapted
- Organisms with the allele for this selected phenotype survive and reproduce whilst passing on the advantageous allele, whilst those without the allele do not. (differential reproductive success)
- Over many generations the frequency of the advantageous allele increases in the population.
What is directional selection? Include an example
Directional selection is when the change in the environment selects for those organisms with allele for a phenotype towards one extreme of a range.
An example of this is antibiotic resistant bacteria.
What is stabilising selection? Include an example
Occurs when the environment is not changing and it selects for organisms with characteristics towards the middle of the range, these organisms then survive and reproduce passing on their alleles to the next generation. Organisms with alleles for the extremes are selected against.
An example of this is human birth weights.
What is a species?
A group of organisms with similar characteristics that can interbreed to produce fertile offspring.
What is courtship behaviour and why is it necessary.
Courtship behaviour is a necessary precursor to successful mating.
It allows organism to:
- recognise members of their own species
- recognise members of the opposite sex
- identify a mate who is capable of breading (ie sexually mature, fertile, biologically fit)
- synchronise mating so that it takes place where there is maximum probability of the sperm and egg meeting
- form a pair bond that will lead to successful mating and raising of offspring.
What is meant by hierarchy?
Where smaller groups are placed within larger groups with no overlap between the groups.
What is meant by the term taxon?
Each group a species is put into is called a taxon (plural = taxa)
List the taxa in order starting with the largest
- Domain
- Kingdom
- Phylum
- Class
- Order
- Family
- Genus
- Species
What is binomial naming?
A name which includes a genus and species.
EG: Homo Sapiens
What is species richness?
A measure of the number of different species in a community.
What does index of diversity describe?
The relationship between the number of species in a community and the number of individuals in each species.
What is the formula for calculating index of diversity?
D= [ N (N - 1)] / [ sum of n(n-1)
N= total number of organisms of all species
n= total number of organisms of each species
What effect do farming techniques have on biodiversity? Include an example
They reduce biodiversity
EG:
ploughing, grazing, deforestation, use of pesticides such as herbicides and insecticides.
List three things that can be compared to measure genetic diversity within or between species.
- the base sequence of DNA
- the base sequence of mRNA
- the Amin acid sequence of the proteins encoded by DNA and mRNA.
