November mock prep- topic 4 Flashcards
gene
section of DNA that codes for a specific sequence of amino acids, making a polypeptide
locus
specific location of a gene on a chromosome
what are the 3 characteristics of the genetic code?
universal-
same for multiple organisms
non-overlapping-
each base sequence only read once
degenerate-
amino acids coded for by multiple triplets
what is the same at the start of every DNA sequence?
the start codon
what marks the end of the DNA sequence?
the stop codon
what are introns?
non-coding sequences found in a gene
what are exons?
coding sequences within a gene
when are chromosomes visible?
when a cell is dividing
what are chromatids?
one of the two strands that make up a chromosome joined at the centromere
how are chromosomes formed?
DNA combines with histone forming a DNA-histone complex
coils then folds to form loops
loops coil and pack together to form the chromosome
what is a homologous pair?
one chromosome from maternal chromosomes and one chromosome from paternal chromosomes
what is an allele?
alternative form of a gene
what happens when the base sequence of a gene changes?
a new allele is produced due to the mutation
this codes for a different amino acid creating a different polypeptide
this therefore creates a different protein
what is a codon?
sequence of 3 bases on mRNA
what is the genome?
complete set of genes in a cell
what is the proteome?
full range of proteins produced by the genome
what is the structure of RNA?
ribose sugar
phosphate group
bases- A-U/ C-G
mRNA
single helix
long strand
transcription
leaves through nuclear pores
acts as template for protein synthesis
information in form of codon
tRNA
small
around 80 nucleotides
anticodon on opposite end- specific to the amino acid
clover leaf shape with one end extended past the other where the amino acid attaches
describe transcription
process of making pre-mRNA
DNA helicase breaks hydrogen bonds exposing the nucleotides in that area, creating a template strand
bases on template strand pair with complementary RNA nucleotides using RNA polymerase
RNA polymerase reaches stop codon and detaches
describe splicing
process of making mRNA
introns removed as they are non coding and would prevent protein synthesis
functional exons are joined
describe translation
1) mRNA leaves through nuclear pore into cytoplasm
2) ribosome attaches to start codon
3) tRNA with complementary anticodon pairs up with codon, carrying a specific amino acid
4) tRNA binds with next codon carrying a different amino acid
5) ribosome moves along mRNA bringing two tRNA molecules each time with amino acids being joined by peptide bonds
6) first tRNA is released when ribosome moves to third codon so it can collect another amino acid
7) process continues until stop codon is reached
what is a mutation?
any change to the quantity or base sequence of the DNA
what are the 3 mutations?
substitutions-
nucleotide replaced by a different one
usually coding for a new amino acid
this doesn’t always happen due to the genetic code being degenerate
deletion-
nucleotide is lost causing a frame shift often completely changing the amino acid sequence
addition-
new nucleotide is added causing a frameshift
what are the two chromosome mutations?
polyploidy-
change in whole set of chromosomes
non-disjunction-
changes in the number of individual chromosomes when chromosomes fail to separate
leads to gamete having one more or one less chromosome
why is meiosis important?
for sexual reproduction
if each gamete was diploid, the cell would produce 92 chromosomes
to maintain a constant number they must be halved at some point
how many daughter cells does meiosis produce?
4 daughter cells (haploid)
describe meiosis
first division:
1) homologous chromosomes pair up and chromatids wrap around each other
2) equivalent portions can be exchanged during crossing over
3) divides with one chromosome from each pair going into one daughter cell
second division:
1) chromatids move apart
2) 2 daughter cells divide to produce 4 daughter cells
how does meiosis produce genetic variation?
independent segregation of homologous chromosomes
new combinations of alleles by crossing over
what is independent segregation?
one of each chromosome pair will go into one of the daughter cells
depends on how they are lined up to which daughter cell they go in
describe crossing over
chromatids of each pair become twisted creating tension, breaking a portion of the chromatids
describe recombination
rejoin with chromatids of its homologous partner
what is genetic diversity?
total number of different alleles in a population
what is a population?
group of individuals of the same species that can reproduce to make fertile offspring
what does genetic diversity enable?
natural selection to occur
when is genetic diversity greater?
with more different alleles
wider range of characteristics
more likely some individuals will survive environmental change
describe natural selection
1) random mutation of alleles within gene pool may result in a new allele
2) this may give the possessor an advantage
3) they will have better chance of breeding successfully and producing more offspring
4) this passes the advantageous allele on to the next generation
5) over time the frequency of the allele increases
what is selection?
process by which organisms better adapted to their environment tend to survive and breed
directional selection
more extreme phenotypes selected for
stabilising selection
favour average individuals- normal phenotype selected for
what are the 3 adaptations?
anatomical
physiological
behavioural
what is courtship behaviour?
individuals can identify other members of their own species by how they act
identify a mate capable of breeding
form a pair bond
synchronise mating
become able to breed
classification
grouping of organisms
taxonomy
theory and practice of biological classification
artificial classification
divides organisms according to differences that are useful at the time
phylogenetic classification
based upon evolutionary relationships
classifies species into groups using shared features
arranges groups into hierarchy
taxon
each group in a phylogenetic biological classification
what are the taxons in the phylogenetic classification?
Domain
Kingdom
Phylum
Class
Order
Family
Genus
Species
mnemonic:
do keep ponds clean or frogs get sick
what is a phylogeny?
evolutionary relationship between organisms represented by a phylogenetic tree
what is biodiversity?
variety of different species in an ecosystem
species diversity
number of different species and individuals within a community
genetic diversity
variety of genes possessed by the individual
ecosystem diversity
range of different habitats
species richness
measure of species diversity
index of diversity
sum of total no. of organisms of all species/ sum of total no. of organisms of each species
impact of agriculture
agricultural ecosystems controlled by humans
genetic variety of alleles reduced as farmers select species for specific qualities
practices removing habitats
removal of hedgerow/ woodland/ ponds
overgrazing
creating monocultures
practices of farming with an indirect effect
use of pesticides
escape if effluent
lack of crop rotation
conservation techniques
maintain hedgerows
plant hedges as field boundaries
create ponds
leave wet corners of fields
organic fertilisers
