Topic 4 Flashcards
what are the similarities between the DNA is euk and pro cells
- both made of DNA nucleotides
- nucleotides joined by phosphodiester bonds to make polymer chain
differences between DNA in euk and pro cells
- euk is longer / pro is shorter
- euk is linear / pro is circular
- euk has histones / pro doesnt associate with proteins
describe the DNA of mitochondria and chloroplasts
- shorter
- circular
- doesnt associate with proteins
what is a gene
a base sequence of DNA that codes for
- amino acid sequence of polypeptide
- a functinal RNA
whats the locus
fixed occupied postion of a gene on a chromosome
how many DNA bases code for an amino acid
three
three features of genetic code
- degenerate
- non-overlapping
- universal
explain the degenerate feature of the genetic code
- theres more than one triplet base that codes for each amino acid
- genetic code has to code for 20 amino acids
- four DNA bases (ATCG) and so therefore three bases are needed to make enough combinations for at least 20 amino acids
> 4 x 4 x 4 = 64 amino acids
why is the degenerate feature an advantage
if a point mutation occurs, despite the triplet bases being different, the coding for the amino acid could still be the same
explain the universal feature of the genetic code
all dna bases code for the same amino acid in all organisms
explain the non-overlapping feature of the genetic code
- each base is only part of one triplet
why is non-overlapping an advantage
if point mutation occurs, only one triplet is affected so only one amino acid will change
what are introns
sections of DNA bases that do not code for polypeptides
> only found in eukaryotic DNA
what are exons
sequences of DNA that code for amino acids
whats a codon
triplet on mRNA that codes for a specific amino acid
whats a start codon
three bases at the start of every gene that initiates translation
whats a genome
an organisms complete set of genes in a cell
whats a stop codon
three bases at the end of every gene that cause ribosomes to detach and stop translation
whats a proteome
full range of proteins that a cell can produce
should genome change
no
> unless theres a mutation
should proteome change
yes > constantly changing depending on what proteins are needed
what does mRNA stand for
messenger RNA
what is mRNA, where is it found and made
- short, single stranded molecules
- found in cytoplasm and nucleus
- made during transcription and is complemnetary to the DNA base sequence
whats tRNA, where is it found
transfer RNA
cytoplasm
describe features of tRNA and what theyre for
- has amino acid attachment site
- anticodon at base of molecule > complementary to mRNA codons
what does tRNA look like
- single polynucleotide strand folded into a clover shape with hydrogen bonds between base pairs to hold the shape
what are the two steps of protein synthesis
transcription and translation
whats transcription
one gene on the DNA stand is copied into mRNA
whats translation
mRNA from transcription joins with a ribosome and corresponding tRNA molecules bring the specific amino acids the codon codes for
outline steps of transcription
- DNA helix unwinds to expose bases to act as a template
- hydrogen bonds broken by DNA helicase between bases
- free mRNA nucleotides align with complementary bases with template DNA strand
- RNA polymerase joins the mRNA nucleotides > forms RNA polymer chain
- leaves nucleus via nuclear pores after modifications
what are the modifications to the pre mRNA before it leaves the nucleus as a mRNA strand
splicing
> the introns are spliced out by a splicesome leaving just the exons (coding regions)
why does transcription in prokaryotes create mRNA directly and not pre mRNA
because prokaryotes DNA do not contain introns
outline steps of translation
- mRNA attaches to a ribosome in the cytoplasm at the start codon
- tRNA molecule with complementary anticodon at its start codon aligns opposite the mRNA > held in place with ribosome
- ribosome moves along one codon along mRNA to allow for another complementary tRNA molecule to attach
- the amino acids delivered by the tRNA are joined with a peptide bond > requires ATP and enzyme
- continues until ribosome reaches stop codon at the end of the mRNA and detaches
why does the stop codon allow for the ribosome to detach
it doesnt code for an amino acid
what is a gene mutation
change in the base sequence
what is the effect of mutagenic agents on gene mutations
random mutations are more likely to occur
examples of mutagenic agents
- high energy radiation
- ionising radiation
- chemicals
what can a gene mutation result in happening to the base sequence
bases being deleted or substituted for different ones
explain what frameshift is
one base is deleted so all of the base codons change and different amino acids could be coded for
why is it possible for a base substitution to have no impact on the overall coding
- genetic code is degenerate
- multiple codons code for the same DNA base
what are chromosome mutations
changes in the number of chromosomes
what is non-disjunction
when chromosomes or chromatids dont split equally during anaphase
or meiosis 1 / 2
what is polyploidy
changes in whole sets of chromosomes
when does polyploidy occur
when organisms have three or more sets of chromosomes rather than two
> common in plants
> fatal in humans
what is aneuploidy
changes in the number of individual chromosomes
how does aneuploidy occur
individual homologous pairs of chromosomes fail to separate during meiosis
what are the two ways variation is introduced in meiosis
independant segregration
crossing over
> occur in meiosis 1
what is independant segregration
when the homologous pairs of chromosomes line up opposite eachother at the equator and the pairs seperate randomly
what is crossing over
when homologous pairs line up opposite eachother at equator and parts of the chromatids twist around eachother
- this causes tension on the chromatids and breaks them
- broken parts of the chromatid recombine with another chromatid > resulting in new combinations of alleles
compare mitosis and meiosis
- meiosis is two divisions / mitosis is one
- meiosis produces haploids / mitosis produces diploids
- meiosis introduces genetic variation / mitosis creates genetically identical cells
how can you identify meiosis in a life cycle
diploid (2n) > haploid (n)
what is genetic diversity
number of different alleles of genes in a population
what is natural selection
process that leads to evolution in populations
what is evolution
change in the allele frequency over many generations in a population
what type of adaptations can natural selection result in
anatomical
physiological
behavioural
outline the process of natural selection
- new alleles for a gene are created from random mutations
- if the allele is advantageous, survival increases > more reproduction
- reproduction passes on the advantageous allele to next generation
- new allele has increased in frequency over many generations
how do you know if organisms are part of the same species
both can have fertile offspring
why is courtship behaviour essential
enables successful mating and for species recognition
what is courtship behaviour
a sequence of actions which is unique to each species to help animals recognise their own species and help reproduction
who usually performs the courtship ritual
the males
how can courtship rituals be observed to conclude the relations between the species
the more similar the ritual, the closer in relation they are
what is phylogenetic classification
arranging species into groups according to their evolutionary origins and relationships
whats the order of hierarchy
domain
kingdom
phylum
class
order
family
genus
species
what is a hierarchy
smaller groups arranged within larger groups
how does binomial system work
first name is genus
second name is species
same species = closely related
what is species diversity
number of diff species and individuals within each species in a community
what is genetic diversity
the variety of genes amongst all the individuals in a population of one species
what is ecosystem diversity
range of different habitats
what is species richness
number of different species in a community
what are farming techniques to balance between conservation and farming
- destruction of hedgerows
- selective breeding
- monocultures
- over-grazing
- filling in ponds and draining wetlands
how do you measure biodiversity
index of diversity
N = total num of organisms of all species
n = total num of organisms of a particular species
D = Simpsons diversity index
(1 is lowest value for D > the higher it is, the greater the species diversity
what can we compare to invesitgate relationships between species
amino acid sequence
mRNA base sequence
DNA base sequence
observable traits
