Biology Exam 4

Watson and Crick

deduced that DNA is from a double helix

Meselson and Stahl

DNA replication is semiconservative

Franklin and Wilsons

Produced DNA photo showing the helical structure

Hershey and Chase

Confirmed that DNA is the genetic material

Chargaff

Found base pairing rules

• A=T, G=C

Griffith

Discovered the ‘transforming principle’ that transfers genetic information

Order of DNA structure

histones → nucleosomes → 30 nm fiber → looped domains → chromosomes

Euchromatin

Less compact, available for transcription

Heterochromatin

More compact, NOT available for transcription

DNA Polymerase 3

Adds nucleotides to the leading strand

• adds 5’ → 3’

DNA Polymerase 1

Replaces RNA primers with DNA

Helicase

unwinds DNA

Primase

Builds RNA Primers and adds to DNA

Okazaki Fragments

segments of DNA on lagging strand

DNA Ligase

Seals okazaki fragments on lagging strand

Topoisomerase

Relieves tension ahead of the replication fork

Single Stranded Binding Proteins

Binds to unpaired DNA strand to keep from repairing

Gene Cloning

Multiple Copies of a Gene

• uses restriction enzymes to cut molecules

• produces sticky ends that H-bond with other sticky ends

Gel electrophoresis

visualization of length of DNA fragments

• DNA goes from negative to positive

Polymerase Chain Reaction (PCR)

Used to amplify a target sequence of DNA to use as a fragment for cloning

• Primers bracket the segment

DNA Sequencing

DNA pol. is used to synthesize a stretch of DNA using a single stranded template

CRISPR-Cas9

Allowing for the editing of genes in a specific, desired way

• uses an RNA sequence to edit genes

Central Dogma

DNA → RNA → Protein

Transcription

DNA is used as a template to make RNA

• occurs in the nucleus (eu.) /cytoplasm (pro.)

Initiation of Transcription

RNA pol. binds to the promoter

• in eukaryotes, it requires transcription factors

Elongation of Transcription

RNA pol. synthesizes RNA 5’ → 3’ on the template strand

Termination of Transcription

Prokaryotes: terminator sequence

Eukaryotes: polyadenylation signal

5’ Cap

Modified Guanine to the 5’ end

• helps ribosomes attach

• protects mRNA from degradation

Poly-A Tail

50-250 adenines to the 3’ end

• extends the mRNA lifespan

• helps ribosomes to bind to mRNA

RNA Splicing

Removes introns

• accomplished by spliceosome

• keeps exons

Alternative Splicing

Removes introns

• exons combined in different ways

• one genes = multiple proteins

mRNA

Carries codon sequences from DNA

• short lived

• template for protein synthesis

tRNA

carries amino acids to ribosomes

• has anticodons to match mRNA codons

• can, and is, reused

rRNA

makes up the ribosome

• long lived

A site of Ribosome

tRNA arrives with amino acid

P site of Ribosome

tRNA puts amino acids into the chain

• fused with peptide bond

E site of Ribosome

tRNA exits the ribosome

Beadle and Tatum

discovered that one gene → one polypeptide

AUG codon

codes for Methionine (Met)

• the ONLY start codon

UGA, UAG, UAA

The stop codons!

Trancription Unit

Promoter: where RNA pol begins transcription

(pro.) Terminator: where transcription ends

Transcription Initiation Complex

Transcription factors → Promoter → RNA pol.

Ribozymes

RNA molecules that act as enzymes and catalyze their own splicing and removal

Translation Initiation Complex

Small subunit + tRNA + Large subunit

Elongation of Translation

Codon Recognition → Peptide Bond Formation → Translocation

Termination of Translation

Stop codon triggers addition of release factor

Point Mutation

Change in a single nucleotide pair

• bad mutation: genetic disorder

Substitutions

replacement of one nucleotide and its pair

Silent Mutation

Has no effect on protein

Missense Mutation

Changes 1 amino acid to another

Nonsense Mutation

Prematurely stops polypeptide formation

Frameshift Mutation

Number of Nucleotides added or deleted aren’t a multiple of three

Mutagens

Mutations from physical or chemical agents

Nucleotide Analogs

Chemicals similar to normal DNA that pair incorrectly during replication

Operon

group of genes that are transcribed together with one promoter

• has an operator: off/on switch

Repressible Operon

default on, but is turned off by a repressor

• used for anabolic (biosynthetic) pathways

Repressor

Turns a Repressible Operon off

• allosteric, meaning it needs a corepressor to activate

Inducible Operon

Default off, but is turned on via inducer

• used for catabolic (metabolic) pathways

Inducer

Binds to repressor and turns it off in an Inducible Operon

Negative Control

Operon is turned off via repressor

• both trp and lac

Positive Control

Regulatory protein turns operon ON

• lac operon via CAP (cAMP receptor protein)

Dual Control

Operon uses BOTH negative and positive control

Differential Gene Expression

same DNA, different function

Epigenetic Inheritance

• Histone Acetylation

• Histone Methylation

Histone Acetylation

addition of acetyl groups

• looses chromatin → Euchromatin → genes are transcribed

Histone Methylation

addition of methyl groups

• tightens chromatin → Heterochromatin → genes are NOT transcribed

Transcriptional Control

controls whether transcription begins

• regulated via promoters, enhancers, and specific and general transcription factors

Specific Transcription Factors

Increases or decreases transcription for particular genes

Post transcriptional control

includes alternative splicing, RNA splicing, and mRNA stability → poly-a tail length

Post Translational Control

Protein Processing: chemical modifications and folding to make it functional

Protein Degradation: when their time is up, proteins are sent to proteosomes for destruction

noncoding RNA

transcribed but not translated

micro RNA (miRNA)

degrades mRNA or blocks translation

small interfering RNA (siRNA)

silences gene expression by degrading mRNA

piwi associated RNA (piRNA)

induces formation of heterochromatin

nucleic acid hybridization

nucleic acid probe detects the presence of specific mRNA

in situ hybridization

detects the presence of a given mRNA in tissue

RT-PCR

detects the presence of a given mRNA in RNA sample

DNA Microarray Assay

identifies sets of genes coexpressed by a group of cells

Epigenetics

environment modifying gene expression without changing DNA sequence

Phosphorylation

increases or decreases gene expression

Whole Genome Shotgun Approach

whole genome is cut into small overlapping pieces and computer software assembles into the entire sequences

Metagenomics

DNA comes from a community of species that is collected and sequenced

Bioinformatics

use of computational tools to analyze, compare, and annotate genomes

• identifies and regulatory elements

• comparing genomes of different species

Proteome

all proteins produced in a cell/tissue

Gene Duplication

creates extra copies of genes

• one has og function, the other can mutate and evolve

Exon Shuffling

exons from different genes recombine → new genes or protein domains

Transposons

moves via a DNA int.

• can or cannot leave a copy

Retrotransposons

moves via RNA int.

• always leaves a copy

Transposable Elements

jumping genes that move within the genome

• transposons

• retrotransposons

Genome Sequences with HIGH similarity

recent divergence

Genome Sequences with LOW similarity

ancient divergence

• helps scientists identify which genes have remained conserved

population

localized group of organisms belonging to one species

gene pool

the total of all the alleles in a population

species

a group of populations who can make fertile offspring

allele frequency

proportion of a specific allele in the gene pool

genotype

allele combination

phenotype

observable traits

fitness

how well an organism passes on its genes relative to others

Mutation

source of all new genetic variation

• creates new alleles

• usually neutral or harmful

Sexual Reproduction

shuffles alleles, doesn’t make new ones

• crossing over

• ind. assortment

• rand. fertilization