Bio Unit 6

Evidence for DNA as genetic material

in nucleus, doubles during S phase, 2 times in diploid cells

Chargaffs Rules

DNA composition varies from one species to the next, base composition of dna varies between species, percentage of bases are equal

Three major differences between DNA and RNA

base pair —> nucleobases, thymine —> uracil, double stranded —> single stranded

DNA structure

nitrogenous bases, sugar phosphate backbone, 5 prime end to 3 prime end

Key features that define DNA structure

anti parallel backbones, uniform pairing with a purine and pyrmidine

Structure function relationship

storage of genetic info—> many nucleotides, complementary base paring —> precise replication during S phase, susceptible to mutations, expression of code and info as phenotypes

Steps for DNA Replication

dna double helix is unwound separate two template strands make them available for new base pairing, added nucleotides form complementary base pairs with template dna, linked phosphodiester bonds

Replication

dna strands split, topoimerase seperates them, primase/RNA polymerase, replication force, single strand binding proteins, helicase

DNA polymerase

enzyme responsible for DNA synthesis

helicase

enzyme that opens the double helix and causes strand separation

single stranded binding proteins

keeps the single strands of DNA separated

primase

puts down small RNA primer necessary for DNA polymerase to bind at the origin of replicaton

topoisonmerase

rotates the dna helix to decrease torque which would shred the helix and shear dna

DNA replication step 1

begin at specific location the origin of replication, bubble in 2 directions, replication fork

Elongation

newly replicated dna stranded must be formed antiparallel to the template strand, elongate only in 5-3 direction

Termination

telomeres and telomerase

Two major repair mechanisms for dna repair

proof reading, mismaten repair, nucleotide exiscion repair

proof reading

dna polymerase proofread newly made DNA, replacing any mispairing

mismaten repair

occurs after replication is complete, recognizes missed mispairings and removes a protion of dna along with the incorrect nucleotide

nucleotide exiscion repair

nuclease cuts out and replaces damaged stretches of DNA

Evolutionary purpose for altered nucleotides

sequence changes may become permanent and heritable, genetic variation natural selection, specifies diversificaiton

spontaneous

permanent changes in genetic material that occur without any outside influence

induced

cause by mutagens, leading to permanent change in the DNA sequence

Importance of DNa

info content of genes form specific sequences of nucleotides in Dna, specific trates dictated by synthesis of proteins, proteins links between genotype and phenotype, gene experession

characteristics of genetic code

universal shared simple bacteria, transplantable genes can be transcribed and translated after being transplanted from one species to another

messenger RNA

produced after the template strand is transcribed

ribosomal rna

catalyze peptide bond formation between amino acids to form a polypeptide

transfer rna

binds to specific amino acids and recognizes and a psecific sequence of nucleotides in rna

template strand

provides a template for orderinf the sequence of comlpemnetary nucleotides in a rna transcript

RNa polymerase

pries dna strands apart, joins together dna nucleo tides, attaches to promotoer region

promoter region

dna region, upstream of a gene

prmoters

signals trancriptional start point and usually extend several dozen nucleotide pairs upstream of the starting point

transcription factors

mediate the binding of rna polymerase and the initiation of transcription

enlongation key components

occurs in 5—> direction, rna polymerase adds rna nucleotides to the template strand, nontemplate strand will have the same sequence as the rna strancript

RNA processing

modification of pre mRNA on obth ends of primary transcript, faciliates export mRNA to cytoplasm, protect mRNA from hydrolytic enzymes

introns

long nonconding streches of nucleotides comprising most eukaryotic mRNA

exons

regions that are usually translated into amino acid sequences

RNA splicing

removes introns and joins exons, creating an mRNA molecule with conitnous coding sequence

alternative RNA splicing

many genes can give rise to two or more different polypeptides, pdeneding on which segments are used as exons

spliceosomes

consists of proteins

tRNA structure and function

translates a mRNA codon into an amio acid using amino acyl rTRNA synthase, brings the amino acid to the ribosome

free ribosomes

synthesize proteins that function in the cytosol

band ribosomes

makes proteins of the endomembrane system and proteins that are secreted from. thecell

ribosome APE

A- amino acids enter, p-polypeptide chain, E-exit side

building a polypeptide

protein factors that aid in the translation processs, energy is provided by hydrolysis of G and P

Initation of translation

mRNA, tRNA, first amino acid, 2 ribosubunits, start codon reads frame, translation iniation complex, initiation factors brings all the components together

Elongation translation

starts with elongation factors, codon recognition, peptide bond fomratino, translocation

termination

ribosome reaches a stop codon, release factor promotes hydrolysis, ribosomal sub units of compnents dissociate

nucleotide pair subsitution

repairs one nucleotide and its partner with another pair of nucleotides

silent mutations

have no effect on the amino acid produced vy a codon because of redundancy in the genetic code

missnese amino acids

still code for an amino acid, not the correct amino acid

nonsense amino acids

change an amino acid codon into a stop codon, always leading to a nonfunctional protein

frame shift mutation

alter reading frame of the genetic message

purpose of gene expresssion

alter gene expression in response ot changing enviornment, develop and maintain multiple cell types

regulation techniques of gene expression

feedback inhibition, gene regulation

repressor

protein that binds to a specific site on the near promoter to prevent transcription, negative regulation

activator

protein that binds to a specific site or near the promoter to stimulate trancription, positive regulation

inducers

compounds that stimulate the trancruption of specific genes

inducible genes

variable activity depending on needs of cell

constituative

expressed at constant rate

operon

group of functionally related genes that share a single promoter

operator

repressor binding site that can bind very tighley with a repressor protein, usually positioned within the promoter

repressible operon

operon that is usually on, binding of a repressor to the operator shuts off transcription

inducible

operon that is usually off, this operon is controlled by a molecule called a inducer which inacitivates the repressor and turnson transcription

repressor

protein that can switch off the operon, prevents gene trancruption by binding to the operator and blocking rna polymerase