Exam 2(post ME 2) Flashcards
Results of transcription, what happens after?
mRNA, rRNA and tRNA. These types of RNA then undergo translation
T.H. Morgan
Showed that genes are located on chromosomes and that chromosomes have 2 components-DNA and protein.
Frederick Griffith
Proved the “transforming principle” of genetic material. He did this in an experiment with 2 types of a virus. S cells killed mice and R cells did not. He found that mice lived when injected with heat-killed S cells but died when injected with a mixture of heat killed S-cells and living R cells. The R cells added carbs, protein and DNA to the heat-killed S-cells
Alfred Hershey and Martha Chase
Showed that DNA is the genetic material of a phage in an experiment in which the protein and then the DNA of the phage were radioactively labeled. The phages were allowed to infect a bacterial cells then a centrifugation was performed and the phage protein was found in the liquid whereas the DNA was found in the solid pellet(bacteria)
Rosalind Franklin
x-ray crystallographic images of DNA enabled Watson to deduce that DNA was helical. She concluded that there were two outer sugar-phosphate backbones with nitrogenous bases paired in the molecule’s interior
Watson and Crick
built models of a double helix to conform to the x-rays and chemistry of DNA, enabled by Rosalind Franklin. Watson built a model in which the backbones were antiparallel
Chargaff’s rules
- The base composition of DNA varies between species
2. In any species that number of A and T bases are equal and the number of G and C bases are equal
of H bonds in A/T and G/C
A and T: 2 H bonds
G and C: 3 H bonds
bases present in DNA and RNA
DNA: A, T, G, C
RNA: A, U, G, C
In what direction does DNA grow
from the 5’ and 3’
DNA structure
double helix with H bonds, complementary strands, antiparallel, more stable than RNA
Models for DNA replication modes
- Conservative model: two strands reassociate after acting as templates for new strands, thus restoring the parental double helix.
- Semiconservative model: two strands of parental molecules separate and each functions as a template for synthesis of a new, complementary strands
- Dispersive model: Each strand of both daughter molecules contains a mixtures of old and newly synthesized DNA
Experiment to determine mode of DNA replication
Bacteria were cultured in medium with heavy N isotope then transferred to medium with a lighter isotope. The sample was centrifuged twice(once after each replication) and the more dense centrifugations went closer to the bottom of the solution. This proved the semiconservative model correct. This rejected both replications of the conservative model and the second replication of the dispersive model.
What DNA replication looks like in bacteria
Happens in a single, circular, chromosome with a single origin of replication
What DNA replication looks like in eukaryotes
Multiple, linear chromosomes, much longer than bacterial chromosomes, multiple origins of replications, occurs in both directions
Helicase
unwinds parental double helix at replication forks
Single-strand binding protein
Binds to and stabilizes single-stranded DNA until it is used as a template
Topoisomerase
Relieves overwinding strain ahead of replication fork by breaking, swiveling, and rejoining DNA strands
Primase
Synthesizes RNA primer at 5’ end of leading strand and at 5’ end of each okazaki fragment of lagging strand, using parental DNA as a template
DNA polymerase I
Removes RNA nucleotides of primer from 5’ end and replaces them with DNA nucleotides adde to the 3’ end of adjacent fragment
DNA polymerase III
Using parental DNA as a template, it synthesizes new DNA strand by adding nucleotides to an RNA primer or pre-existing DNA strand, elongates leading strand continuously in the 5’ to 3’ direction as fork progresses
DNA ligase
Joins okazaki fragments of lagging strand; on leading strand, join 3’ end of DNA that replaces primer to rest of leading strand DNA. Also performs this function in proofreading and repairing DNA
Overall purpose of DNA polymerases
Catalyze the synthesis of new DNA by adding nucleotides to the 3’ end of a preexisting chain. They also repair damaged DNA by filling in missing nucleotides, suing the undamaged strand as a template
direction of DNA elongation
5’ to 3’, leading strand is elongated continuously in the 5’ to 3’ direction as the fork progresses
synthesis of lagging strand
synthesized discontinuously, synthesized as a series of okazaki fragments which are joined together by DNA ligase. Primase makes RNA primer from 5’ to 3’ starting closer to the replication fork and moving away, the DNA pol III makes an okazaki fragment starting at the end of the primer furthest from the fork. Then they both detach and repeat this closer to the replication fork. DNA pol I replaces RNA with DNA, DNA ligase bonds fragments
Ends of leading and lagging strands
leading strand is 5’ to 3’, lagging is 3’ to 5’
trombone model
a recently supported model of DNA replication in which DNA polymerase molecules “reel in” parental DNA and extrude newly made daughter DNA
nuclease
enzyme that cuts damaged DNA strand at 2 point, removing the damaged section
Eukaryotic chromosome structure components from smallest to largest
- DNA: double helix, 2nm in diameter
- nucleosome: 10nm in diameter, histones wrapped in DNA with histone tails sticking out
- Fiber: 30 nm in diameter, many nucleosomes
- Looped domain: 300 nm in diameter, has scaffolding pattern, fiber
- chromatid: 700nm
- Chromosome: 1400nm, 2 chromatids
General mechanisms of gene regulation
- structural and chemical changes to the genetic material
- binding of proteins to specific DNA elements to regulate transcription
- Mechanisms that modulate translation of mRNA
operons
clusters of genes with one promoter, serving several adjacent genes
operator
site of DNA that switches operon on or off, resulting in coordinate regulation of genes, part of operon
repressible operon
usually on, repressors bind to them to shut off transcription
inactive repressor
repressor with no corepressor present
active repressor
repressor with corepressor bound
tryptophan
a co-repressor that activates the repressor, therefore turning the operon off
inducible operon
usually off, inducers inactivates repressor and turns on transcription
Lactose
when present, allolactose acts as an inducer to inactive the repressor and turn on the operon. It promotes the transcription of the enzymes that use lactose
histone tails
protrude outward from a nucleosome, providing amino acids that are available for chemical modification
Acetylation/unacetylated histone tails
acetylation of histone tails promotes loose chromatin structure that permits transcription. Unacetylated histone tails are compact and DNA is not accessible for transcription
Purpose of alternative splicing
allows for an increase in the size of the proteome while maintaining the size of the genome, conserves energy by not increasing genome size
miRNA
microRNA, binds to target mRNA. If the bases are complementary, the mRNA is degraded, if the match isn’t complete, translation is blocked
What do all viruses have?
Genome and a capsid protein coat
Viral genome
may consist of either double stranded or single stranded DNA or RNA
What do all viruses NOT have?
cell membranes, ribosomes, cell walls, organelles
Viral envelope
extra layer of protection found in SOME viruses
How do viruses affect host gene expression?
They make the host cell, replicate viral genome, transcribe viral genes and translate viral proteins
HIV
Virus that causes AIDS. It is a retrovirus that uses reverse transcriptase and infects helper T cells
CRISPR-Cas system
- Infection by phage triggers transcription of the CRISPR region of the bacterial DNA, where phage has inserted its DNA.
- RNA transcript is processed into short RNA strands
- Each short RNA strands binds to a Cas protein, forming a complex
- Complementary RNA binds to DNA. Cas protein cuts the phage DNA
- Phage DNA can no longer replicate
How do scientist take advantage of viral element that control gene expression?
They give “guide RNA” to a Cas9 protein to target a gene, making a Cas9-guide RNA complex. It will then cut the target part of the gene. The target gene can then be isolated so its function can be studied, or if it has a mutation it can be repaired
siRNA
stands for small interfering RNA
Methlyation
methylation of DNA increases its density and decreases expression of methylated genes
promoter
sequences of DNA(a control element) that are part of the operon where RNA polymerase first binds to start transcription
where do transcription and translation occur?
Transcription: nucleus
Translation: cytoplasm
Enhancers
Region of DNA(a control element) that can be bound by activators to increase the likelihood that transcription of a particular gene will occur, transcription factors can also bind to enhancers
transcription factor
proteins that turn specific genes on or off by binding to nearby DNA.
Activators
transcription factors that boost a gene’s transcription
control element
region of DNA that allows the regulation of gene expression by binding of transcription factors
Mendel definition of a gene
discrete unit of inheritance that affects phenotypic character
Morgan definition of inheritance
specific loci on chromosomes
One gene-one enzyme hypothesis
Hypothesis by beadle and Tatum, included that not all proteins are enzymes
One gene-one protein hypothesis
Many proteins are constructed from two or more different polypeptide chains, and each polypeptide is specified by its own gene
One gene-one polypeptide hypothesis
still not entirely accurate, a eukaryotic gene can code for a set of polypeptides via a process called alternative splicing
General definition of transcription
Synthesis of RNA using information in DNA, produces mRNA
General definition of translation
synthesis of a polypeptide using the information in mRNA
Role of RNA in transcription and translation
bridge between genes and proteins for which they code