higher biology unit 1

nucleotide

deoxyribose sugar, phosphate, and base

components of DNA

nucleotides, sugar-phosphate backbone, and bases

DNA structure

anti-parallel, double helix, double stranded

genetic code

the base of sequence of DNA

eukaryotic DNA

linear chromosomes in nucleus, tightly coiled and packaged with histones, and circular chromosomes in chloroplasts and mitochondria

prokaryotic DNA

single, circular chromosomes and smaller plasmids

structure of a nucleotide

base connected to deoxyribose which is held together by hydrogen bonds, and the sugar is connected to a phosphate

structure of a DNA stand

made up of repeating units of nucleotides, held together by hydrogen bonds between complementary bases

organisation of DNA in prokaryotic cells

circular chromosomes, not associated with histones, free in cytoplasm, and extra circular plasmids

organisation of DNA in eukaryotic cells

linear chromosomes, associated with histones, membrane bound nucleus, and circular chromosomes in chloroplasts and mitochondira

DNA polymerase

replicates DNA, needs primers to start, adds nucleotides from 3’ to 5’ ends of forming DNA strand

primer

short strand of nucleotides which binds to 3’ end of template strand

DNA replication

• DNA unwound and hydrogen bondds broken to form two template strands

• leading strand is replicated continuously

• lagging strand is replicated in fragments

• fragments are joined together by ligase

PCR

amplifies DNA using complementary primers for specific target sequences

PCR primers

short strands of nucleotides which are complementary to specific target sequences at the two ends of the region to be amplified

PCR process

• DNA heated between 92 and 98°C to seperate the strands

• DNA cooleed between 50 and 65°C to allow primers to bind to target sequences

• DNA heated again between 70 and 80°C for heat toleant DNA polymerase to replicate the region of DNA

PCR practical applications

• amplify DNA to help solve crimes

• settle paternity suits

• diagnose genetic disorders

DNA replication requirements

ATP, enzymes, nucleotides, primers and DNA template

leading strand

• continously replicated

• DNA polymease adds nucleotides to the 3’ deoxyribose ended strand

lagging strand

• replicated in fragments

• nucleotides can’t be added to phosphate end as DNA polymerase can only add nucleus in a 5’ to 3’ direction

• joined together by ligase

gene expression

transcription and translation of DNA sequences, only a fraction are expressed

different types of RNA involved in gene expression

mRNA, tRNA, and rRNA

codon

triplet of bases on mRNA

anticodon

triplet of bases on tRNA which codes for a specific amino acid

tRNA structure

folded, anticodon with specific amino acid

ribosome structure

protein and rRNA

transcription process

• RNA polymerase unwinds DNA and breaks hydrogen bonds

• RNA polymerase synthesises the primary mRNA transcript by complementary base pairing

RNA splicing

• introns from primary mRNA transcript are removed

• exons joined together in order to form mature transcript

primary transcript journey

mRNA transcribed from DNA in nucleus, and carries complementary copy of code to a ribosome in the cytoplasm

translation process

• begins at start codon and ends at stop codon

• anticodons bond to codons by complementary base pairing

• peptide bonds join amino acids toether in sequence

• tRNA leaves the ribosome as polypeptide is formed

alternative RNA splicing produces

different mRNA transcripts and different proteins

phenotype

determined by the proteins expressed and the environment

mRNA

• carries a complementary copy of the DNA code from the nucleus to the ribosome

• transcribed from DNA in the nucleus and translated into proteins by ribosomes in the cytoplasm

cellular differentiation

when a cell expresses certain genes to produce proteins characteristics of that specialised cell

meristems

unspecialised cells in plants that can divide and self renew

stem cells

unspecialised cells in animals that can self renew and differentiate

embryonic stem cells

• pluripotent

• can differentiate into all cell types that make up an organism

• all genes can be switched on

• can self renew in a lab

(adult) tissue stem cells

• multipotent

• can differentiate into all cell types found in a particular tissue

• are involved in growth, repair, and renewal of cells in that tissue

stem cell theuraptic uses

• repair of damaged organs/ tissues

• treating blood diseases (e.g. leukaemia through bone-marrow transplants)

stem cell research uses

• disease development

• drug testing

• cell processes

genome

• the genome of an organism is its entire hereditary infomation encoded in DNA

• made up of genes and other DNA sequences not coding for proteins

genes

DNA seqeunces that code for proteins

mutation

change in structure or amount of an organisms DNA

single gene mutations

• substitution of nucleotide

• insertion of nucleotide

• deletion of nucleotide

missense mutation

• when one amino acid is changed for another

• can result in a non functional protein or have little effect

nonsense mutation

• when an amino acid is changed for a premature stop codon

• can result in a non functional protein or shorter protein

splice site mutation

• alteration in DNA at the boundary of an intron and an exon

• can result in some introns being retains, or exons not in the mature transcript

frame shift mutation

• all codons and amino acids after mutation are changed

• results in a non functional protein

• e.g - deletion/ insertion

chromosome structure mutations

changes in chromosome mutations are often lethal

deletion

where a section of chromosome is removed, e.g - critical du chat

inversion

where a section of chromosome is reversed

duplication

where a section of chromosome is added from its homologous partner

translocation

where a section of chromosome is added to another chromosome

importance of mutations and gene duplication in evolution

duplication allows for potential beneficial mutations to occur in a duplicated gene, while the original gene can still be expressed to produce its protein

evolution

changes in organisms over generations as a result of genomic variations

natural selection

non random increase in frequency of DNA sequences that increase survival and the non random reduction in frequency of deleterious sequences

stabilising selection

when an average phenotype and extremes of the phenotype range are selected for

directional selection

when one extreme of the phenotype range is selected for

disruptive selection

when two or more phenotypes are selected for

horizontal gene transfer

genes transferred between individuals in the same generation

vertical gene transfer

genes transferred from parent to offspring as a result of (a)sexual reproduction

natural selection is more rapid in..

pokaryotes as they exchange genetic information horizontally, resulting in faster evolutionary change than in organisms using vertical gene transfer

speciation

generation of new biological species by evolution as a result of isolation, mutation, and selection

species

a group of organisms capable of interbreeding and producing fertile offspring which don’t normally breed with other groups

importance of isolation barriers

prevents gene flow between sub-populations during speciation

geographical barriers

lead to allopatric speciation as organisms cannot meet to interbreed

ecological barriers

lead to sympatric speciation due to different habibtats, ph, breeding areas etc.

behavioural barriers

lead to sympatric speciation due to different mating times, or complex mating rituals

genomic sequencing

the process by which the sequence of nucleotide bases can be determined for individual genes and entire genomes

bioinformatics

computers can be used to identify base sequences by looking for sequences similar to known genes and using statistical analyses

genomes from different species that can be sequenced are

• disease causing organisms

• pests

• model cells for research

comparison of genomes shows

many genes are highly conserved across different organisms

phylogenetics

study of evolutionary relationships of different species (e.g. archea, bacteria, eukaryotes), or groups of organisms by using sequence data and fossil evidence

sequence divergence

where sequence data shows estimated time since lineages diverged

evolution of life - main sequence of events:

cells, last universal ancestor, prokaryotes, eukaryotes, multicellularity, animals, vertebrates and land plants

molecular clocks

show when species diverged during evolution and assume a constant mutation rate, and show differences in DNA/ amino acid sequences

predictive medicine

when an individual’s genome is analysed to predict the likelihood of developing certain diseases

pharmacogenetics

use of genome information in the choice of drugs, this can be used to select the most effective drugs and dosage to treat ones’ disease