DNA, protein synthesis and natural selection Flashcards
DNA semi conservative replication requires
Free nucleotides
DNA helicase to unzip the double helix
DNA polymeraseto join nuceotides together
Steps of DNA replication semi conservative
- DNA helicase unzips the original DNA double helix
- Free nucleotides from the cytoplasm pair to the original bases on the original strands of DNA
- DNA polymerase joins the new nucleotides together
- The enzyme rewinds DNA into a double helix and 2 copies are made w/ one strand new and one strand old (semi conservative)
Evidence for semi conservative replication stahl
Used E. coli with density gradient configuration
- Labeled DNA of a strand of Ecoli bacteria with N15 so it would only have that isotope
- Transferred the cultured bacteria to A tube of N14 and allowed the. To replicate once
- He took a sample of the 1st replication and did thus 4 times
Stahl results
Parent - only N15 1st gen- 100% mix of N15 and N14 2nd gen - 50% N14 50% mix 3rd gen - 75% N14 25% mix 4th gen - 87.5% N14 12.5% mix
What stahl was dependent on
All bases contains nitrogen
N having two isotopes
The bacteria corporations N from their growing medium into any new DNA made
Genome
Complete set of genes in an individuals DNA
Genes
A segment of a DNA molecule that codes for the synthesis of a single polypeptide
Proteome
Full range of proteins an individual can produce
Codon
Sequence of three bases that codes for a specific amino acid
Stop codon UAG
Protein synthesis
mRNA is transcribed from DNA in the nucleus to produce a single stranded RNA
The mRNA strand is complementary to the DNA base sequence
mRNA travels from the nucleus to the ribosomes in the cytoplasm
Ribosomes are proteins that translate mRNA into amino acids and synthesis the polypeptide
tRNA forms a clover like shape and is vital for translation. It then reads the mRNA codons and brings the corresponding amino acids int the ribosomes
Each tRNA molecule has a specific anticodon which is complementary to a codon on mRNA
The amino acid that corresponds to that specific anticodon binds to a specific attachment site on the tRNA molecule
1st stage of protein synthesis
- transcription
RNA polymerase bind to the locus of the gene to be transcribed (trhe target gene)
The H bonds between the 2 DNA strands breaks when RNA polymerase binds to DNA leaving the bases of the target gene exposed as the two strands separate.
RNA polymerase binds free floating RNA nucleotides to the template strand (template strand is a DNA strand that is complementary to the base sequence of the target gene)
These nucleotides form a strand of mRNA which is a copy of the gene which is a copy of the gene
The free floating nucleotides are joined together by RNA polymerase. Phosphodiester bonds form between the nucleotides in a condensation reaction
RNA polymerase eventually reaches a stop codon (UAG)
The mRNA strand is separated from the template strand by RNA polymerase the H bonds between DNA strands form a again
The completed mRNA strand leaves the nucleus and enters the cytoplasm and is then used in translation
Stage 2 of proteinsynthesis
- translation
mRNA bind to the ribosome in the cytoplasm - the ribosome is the site of proteinsynthesis
One molecule of tRNA binds to the first codon in the ribosome. The tRNA molecule has an anticodon specific to a complementary codon
Each tRNA molecule carries a specific amino acid into the ribosome. The amino acid is bound to tRNA using ATP
The tRNA molecule binds to the second codon in the ribosome. When a tRNA molecule binds to mRNA the corresponding amino acid Is brought to the ribosome the 2 amino acids form a peptide bind between the two.
The ribosome moves along the mRNA strand so that a new codon enters the ribosome and the process repeats
When the ribosome reaches a UAG codon there is no corresponding tRNA molecule and the polypeptide chain us released from the ribosome
The chain then completes its function as. A protein
mRNA in eukaryotes
Called pre-mRNA
Sliced before translation to remove non-coding sections
RNA polymerase only produces mRNA
mRNA in prokaryotes
No splicing
RNA polymerase catalysts every step of transcription
Non coding genes
Coding genes
Introns
Extrons
Genetic code is…
Degenerate - some amino acids are coded by more than one codon
Universal - TACG used in every organism
Mitosis definition
A sexual cell duplication for growth and repair
For a 2 identical daughter cells
Major phases of mitosis
Interphase and mitotic-phase
I.P.M.A.T
Interphase ( general )
G1 - cell grows
S - DNA synthesis
G2 - cell grows
Mitotic phase
Replicated DNA and cytoplasmic contents are are separates Prophase Metaphase Anaphase Telophase
Interphase (IPMAT)
Cell prepares to divide
Semi-conservative replication- organelles replicated
More ATP produced to be used in division
Prophase
Nuclear envelope breaks down so the chromosomes are free in the cytoplasm
Chromosome coil more tightly and become tighter and can be seen by a microscope
Centrioles move to opposite poles of the cell
Microtubules form the mitotic spindle fibres between centrioles
Metaphase
Chromosomes line up down the middle of the cell and maximally condensed. They attach to spindle fires at the centromere
Anaphase
Chromosomes separate onto 2 sister chromatids
Each sister chromatid is pulled to opposite poles of the cell
Telophase
Chromatids reach the opposite poles and de-condense. Nuclear envelopes form around the chromosomes
There are 2 nuclei and cytokinesis takes place as the cell membrane split at the cleavage furrow and 2 identical daughter cells are formed
Investigating mitosis
Root tip meristem tissue experiment
Root tip experiment
Place sample in 5cm HCl Cut tips 2mm 2-3 drops of stain 2mins Spread with needle and place cover slip and apply force to remove bubbles Figure out mitotic index
Mitotic index =
( Number of cells in mitosis/ total cells ) x 100
Cancer drugs
Can target damaged DNA in S phase to kill cells and parent tumours
Can inhibit G1 to halt cell cycle and Kill cells
Addition mutation
One or more bases added to DNA sequence
Deletion mutation
When one or more bases are removed from the sequence
Substitution mutation
One or more bases changed in the sequence
Causes of mutation
Errors in DNA replication Mutagenic agents ( radiation )
Chromosome mutations In meiosis ;
Can effect the number of chromosomes in developing zygote
Non- disjunction is where sister chromatids don’t separate properly
Meiosis definition
Sexual cell division of 2 gametes that results in 4 non identical daughter cells
Gametses
The sex cells that fuse to form a new diploid organism ( an organism with 2 copies of each chromosome)
Factors that inc genetic diversity
Random fertilisation
4 genetically different daughter cells each with a different combos of chromosomes
Chromosomes split into random combinations (independent segregation)
Stages of meiosis
- The chromosomes in the cells replicate to produce an identical copy of each other ( chromatids ) these chromatids condense to form a double armed chromosome
- Homologous pairs are arranged in the centre of the cell ( moved my spindle fibres)
- The homologous chromosomes are separated randomly and pulled to opposite sides by spindle fibres. Random combos of chromosomes are pulled to each side of the cell
- Cell divides in 2 with one chromosome from each pair in each cell creating 2 genetically different cells with 1/2 the number or chromosomes (meiosis 1)
- The sister chromatids are separated by spindle fibres and pulled to opposite side of the cell
- This then divides into 2 cells with one sister chromatid in each cell (meiosis 2)
What happens when the homologous pairs are arranged down the middle
Section do DNA are swapped between paired chromosomes ( crossing over) this produces a combo of alleles
Allele
Variations on a specific gene
Genetically variation allows _________ ___________ to take place
Natural selection
Natural selection
Actors on a population to inc frequency of advantageous alleles to increase chances for a species to survive and reproduce and to select out any harmful alleles
Mutations are
Spontaneous and change the sequence of DNA resulting in new alleles of a gene
Evolution is
The change in allele frequency over time
Natural selection acts on an individual by…
Imposing a selection pressure
What is a selection pressure
A factor that influences the reproductive success of an individual
Stabilising selection
Favours the average and selects against the extremes
Takes place in an environment that does not change
Eg human birth weight
Directional selection
Favours 1 extreme causing one new mean
Takes place when the environment has experienced a change
Eg. Antibiotic resistance
Disruptive selection
Selects against the mean and favours both extremes causing 2 new means
Change in a physical structure
Anatomical adaptation
Eg. Giraffe long neck
Changes within the body
Physiological adaptation
Eg snake venom or shivering
Changes in behaviour
Behavioural adaptation - can be learnt or inherited
Eg spiders web
