Section 4 Flashcards
Genetic information, variation and relationships between organisms
Describe the structure of DNA in eukaroyotic cells
Linear, long DNA which exists as chromosomes found in the nucleus
Wound around proteins called histones
The mitochondria and chloroplasts have their own DNA which is similar to prokaryotic cells becuase it is circular and shorter
Describe the structure of DNA in prokaryotic cells
DNA in chromosomes but is shorter and circular
No histones
What is a gene?
DNA contains genes
It is a sequence of DNAbases that codes for a polypeptide or functional RNA
What is a genome and a proteome?
Genome - complete set of genes in a cell
Proteome - the full range of proteins that the cell is able to produce
What are introns and exons?
Introns - sections of DNA which don’t code for amino acids
Exons - genes that do code for DNA
What is an allele?
Different forms of the same gene
What are homologous chromosomes?
Pairs of matching chromosomes with the same size and genes but with different alleles
What is a locus?
Fixed position of an allele on the chromosome
Alleles coding for the same characteristic will be found in the same place
Describe mRNA
Made during transcription
Carries the genetic code from the DNA to the ribosomes where it is used to make a protein during translation
A single polynucleotide strand
Has codons/ triplets - three bases which code for an amino acid
Describe tRNA
Carries amino acids to the ribosomes
Single polynucleotide strand folded into a clover shape
H bonds between specific base pairs hold the shape
Has an anti codon - a specific sequence of three bases
Amino acid binding site at the other end
Describe transcription
RNA polymerase attaches to DNA and breaks H bonds between the two strands
One of the strands is used as a template
RNA polymerase lines up free RNA nucleotides to complimentary base pairs with uracil instead of thymine
RNA polymerase joins the nucleotides making an mRNA strand
When RNA reaches a stop signal it detaches from the DNA
mRNA moves out of the nucleus and attaches to a ribosome
What is splicing?
When introns are removed from pre - mRNA
Takes place in the nucleus
Doesn’t happen in prokaryotic cells as there are no introns
Describe translation
mRNA attaches itself to a ribosome and the tRNA molecules carry amino acids to it
ATP provides energy needed for the bond between the amino acid and the tRNA molecule to form
A tRNA molecule with an anti codon that is complimentary to the codon on the mRNA attaches by complimentary base pairing
A second tRNA molecule attaches in the same way
These two amino acids are joined by a peptide bond
The first tRNA molecule moves away leaving the amino acid behind
A third tRNA molecule binds and the second tRNA molecule moves away until there is a stop codon
What is the genetic code?
Sequence of codons in mRNA
What does non- overlapping mean?
Each codon is read in sequence
Bases don’t share their bases
What does degenerate mean?
there are more possible combinations of codons than there are amino acids
Some amino acids are coded for by more than one codon
What does universal mean?
codons are all the same for all living things
What does diploid mean?
Normal body cells have the diploid number of chromosomes meaning each cell contains two of each chromosome - one from mum and one from dad (46 chromosomes)
Describe the process of meiosis
1) DNA unravels and replicates so there are two copies of each chromosome called chromatids
2) The DNA condenses to from double armed chromosomes each made from two sister chromatides joined by a centromere
3) Meiosis 1 - the chromosomes arrange themselves into homologous pairs
4) These are seperated
5) Meiosis 2 - the pairs of sister chromatides that make up each chromosome are seperated
6) Four haploid cells that are genetically different are produced
What causes genetic variation in gametes?
Crossing over of chromatids
Independaent segregation of chromosomes
Random fertilisation
Describe crossing over of chromatids
In meiosis 1 homologous chromosomes come together to pair up
The chromatids twist around each other and bits of chromatids swap over
The chromatids contain the same genes but a different combination of alleles
Describe independant ssegregation of chromosomes
Each homologous pair of chromosomes is made up from one chromosome from mum and one from dad
When the homologous pairs are seperated in meiosis 1 it is random to which chromosome from each pair ends up in which cell
Resulsting in different combinations of mum and dad chromosomes
What is a mutagenic agent and an example?
Things that increase the rate of mutations
Radiation, chemicals, viruses
What is genetic diversity?
the number of different alleles of genes in a species or population
How is genetic diversity increased?
Mutations in the DNA forming new alleles
Different alleles being introduced into a population (gene flow)
Describe the process of natrual selection
1) A mutation occurs leading to a new allele which can be advantageous
2) Individuals with this allele are more likely to survive and reproduce and pass the allele on than those without it
3) Allele frequency increases leading to evolution
What is evolution?
The gradual change in a species over time
What is an adaptation and what are the three types?
Features that help organisms to survive in their enviroment
Behavioural
Physiological
Anatmoical
What are behavioural adaptations?
The way an organism acts that increases its chance of survival
e.g playing dead
What are physiological adaptations?
Processes inside an organisms body that increase its chance of survival
e.g when bears hibernate their metabolic rate slows down to conserve energy
What are anatomical adaptations?
Structrual features of an organisms body that increase its chance of survival
e.g Whales having blubber
What is directional selection?
Individuals with alleles for characteristics of an extreme type are more likely to survive and reproduce
Could be in response to an enviromental change
What is stabilising selection?
Individuals with alleles for average characteristics (middle range) are more likely to survive and reproduce
When the enviroment isn’t changing
What is the taxonomy group names?
Kingdom
Phylum
Class
Order
Family
Genus
Species
What three ways can we classify using DNA or proteins?
Genome sequencing
Comparing amino acid sequences
Immunological comparisons
What is genome sequencing?
Comparing the DNA base sequence between different organisms to see how closely related they are
What is interspecific/ intraspecific variation?
Inter - variation between different species
Intra - variation within the same species
What is standard deviation?
A mesure of the spread of values around the mean
What is biodiversity?
the variety of living organisms in an area
What is a habitat?
Where an organism lives
What is a community?
All the populations of different species in a habitat
What is species richness?
A measure of the number of different species in a community
What is a species?
A group of similar organisms which can breed to produce live fertile offspring
What is the equation for index of diversity?
d = N(N-1)
————–
∑ n(n-1)
N = total number of organisms of all species
n = total number of organisms of one species
∑ = sum of
