Bio 3.4

Created by

Maisie Green

Cards (102)

What are the 2 structural things that both eukaryotic and prokaryotic DNA share?
Made of DNA nucleotides containing deoxyribose, phosphate and nitrogenous base
Nucleotides are joined together by phosphodiester bonds to make a polymer chain
3 characteristics of euk dna
longer
linear
histones
3 characterists of pro dna
shorter
circular
no histones
characteristics of mitochondria and chloroplast dna
short
circular
no histones
what is a gene
a base sequence of DNA that codes for the amino acid sequence of a polypeptide and a functional RNA
what is a locus 
Location of a gene on a chromosome
what are the 3 characteristics of the genetic code
degenerate

universal

non-overlapping
explain what is meant by the genetic code being degenerate
each amino acid is coded for by more than one triplet of bases

eg: tyrosine is coded for by ATA and ATG
explain what is meant by the genetic code being universal
the same triplet of bases codes for the same amino acid in all organisms
explain what is meant by the genetic code being non-overlapping
each base in a gene is only part of one triplet of bases that codes for one amino acid
what are introns
sections of DNA that do not code for polypeptides
found in euk DNA not in pro DNA
what are exons
the sequences of DNA that do code for amino acids
what is a codon 
3 bases on mRNA that codes for a specific amino acid
what are start and stop codons
Start : three bases at the start of every gene that initiate translation
Stop: three bases at the end of every gene that cause ribosomes to detach and therefore stop translation
what is a genome 
an organisms complete set of genes in a cell
what is a proteome 
the full range of proteins that a cell is able to produce
what is mRNA 
short, single stranded molecules
found in the cytoplasm and nucleus
it is made during transcription - it is copied from DNA and is therefore complementary to the DNA sequence.
in mRNA, groups of 3 adjacent bases are called codons
what is tRNA
involved in translation

carries the amino acids that are used to make proteins to the ribosomes

tRNA is a single polynucleotide strand that is folded into a clover shape

H bonds between base pairs hold the shape

each tRNA molecule has a sequence of 3 bases called an anti-codon
what are the 2 steps of protein synthesis
1. Transcription
2. Translation
describe the process of transcription
1) DNA helix unwinds to expose bases
2) one chain of DNA acts as template
3) unwinding is catalysed by DNA helicase
4) DNA helicase breaks H bonds
5) free mRNA nucleotides align opposite exposed complementary bases
6) RNA polymerase joins RNA nucleotides to create new RNA polymer chain
7) mRNA is modified and leaves the nucleus through nuclear pores
what is pre-mRNA
mRNA which contains introns

introns are spliced out, leaving just the exons
describe the process of translation
1) mRNA attaches to a ribosome
2) ribosome attaches at the start codon
3) tRNA molecule with complementary anti-codon to the start codon aligns opposite the mRNA
4) ribosome moves along one codon on the mRNA molecule
5) the 2 amino acids are joined by a peptide bond
6) this continues until the ribosome reaches the stop codon, causing the ribosome to detach
what is a mutation 
a change in the base sequence of the DNA, gene mutations occur randomly during DNA replication
what are the types of gene mutation
substitution, insertion, deletion
what is a chromosome mutation
mutation in the number of chromosomes can arise spontaneously by chromosome non-disjunction.
what is non-disjunction
when chromosomes or chromatids don't split equally during anaphase
What are the 2 ways that chromosome non-disjunction can occur?
Polyploidy - changes in whole sets of chromosomes
Aneuploidy - changes in the number of individual chromosomes
What does meiosis produce?
Genetically different from each other and 4 haploid daughter cells
How is variation introduced in variation?
Independent segregation
Crossing over
Explain independent segregation.
Homologous pairs line up opposite each other at the equator of the cell
It is random which side of the equator the paternal and maternal chromosomes from each homologous pair
These pairs are separated, so one of each homologous pair ends up in the daughter cell
Explain crossing over in meiosis.
When homologous pairs line up, chromatids can become twisted around each other
This put tension on the chromatids, causing parts to break
The broken parts of the chromatid recombine with another chromatid
Results in a new combination of alleles
What are the main differences between meiosis and mitosis?
Meiosis has 2 nuclear division whereas mitosis has 1 nuclear division

Meiosis produces haploid cells whereas produces diploid cells

Meiosis introduces genetic variation whereas mitosis produces genetically identical cells
What is genetic diversity? 
the number of different alleles of genes in a population

one factor that enables natural selection
What is natural selection? 
the process that leads to evolution in populations
What is evolution?
the change in allele frequency over many generations in a population
The process of natural selection:
- new alleles are created by random mutations
- if new allele increases chance of survival, they are more likely to survive and reproduce
- reproduction passes on advantageous allele
- over many generations, new allele increases in frequency
What is directional selection?
One of the extremes has selective advantage
Occurs when a change in the environment
What is stabilising selection?
Occurs when environmental conditions stay the same. Individuals closest to the mean are favoured, and any new characteristics are selected against. Results in low diversity.
What is disruptive selection? 
favors individuals at both extremes of the phenotypic range
Define species.
group of organisms that can interbreed and produce fertile offspring