cell bio exam 3

what did watson and crick discover?

the double helix of DNA. 1953.

What did TH morgan discover?

genes are located on chromosomes. 1926.

what did frederick griffith discover?

found that nucleic acid shared genetic material not proteins. 1928.

what was the experiment that determined nucleic acid shared traits not proteins?

injected a mouse with either a pathogenic or non pathogenic bacteria. when the mouse was injected with a heat treated pathogenic bacteria, the mouse lived (showed not proteins). when the mouse was injected with both the heat treated pathogen and pathogen virus, the mouse died (the nucleic acid had to have transferred to the living virus. not the protein bc the protein was dead).

bacteriophage

injects DNA into bacteria and kills by replicating harmful DNA

what did Hershey and chase discover?

bacteriophages inject DNA to kill the bacteria not protein. 1952

what was the experiment that determined bacteriophages injected DNA not protein.

ran 2 trials using radioactive tags. in the first experiment tagged protein with S35, centifuged, and then found that the radioactive material was not in the bottom pellet containing the injected cells. in the second experiment tagged DNA with P32, centrifuged, then found that the radioactive material was in the cell, not in the excess liquid.

what did chargaff discover?

DNA compositions vary by species and there are equal amounts of A/T and C/G. 1950

what did rosalind franklin discover?

used x-ray crystallography to find structure of DNA. 1950. then used those measurements to identify that A/T and C/G must go together based on measurements.

what did watson discover?

used franklins images to suggest that DNA had a double helix structure and base pairs must purine and pyramidines.

how many hydrogen bonds do A and T have?

2

How many hydrogen bonds do C and G have?

3

what does DNA being anti-parallel mean?

one side is 3’ to 5’ and the other is 5’ to 3’

what did meselson and stahl discover?

DNA replication follows the semiconservative model

conservative model of DNA replication

the parent DNA splits and creates copies, then the parent strands and copy strands bind to themselves

semiconservative model of DNA replication

the parent DNA splits, each parent molecule produces a copy and stays with the copy

dispersive model of DNA replication

the parent DNA splits and bits and pieces are replicated to create new combined strands

how did meselson and stahl determine that DNA was replicated via the semi-conservative model?

grew bacteria in heavy nitrogen ($^{15}\text{N}$) and then moved them to light nitrogen ($^{14}\text{N}$). after centrifuging, the first generation produced DNA with intermediate density (1 band), and the second generation produced both intermediate and light DNA bands (2 bands). this proved that each new DNA molecule keeps one parent strand and gains one new strand, aka semi-conservative replication

how is DNA in eukaryotic cells replicated?

It creates bubbles in the DNA that expand outwards, allowing replication to occur simultaneously at multiple sites along the strand.

Helicase

Unwinds the parental DNA double helix at the replication forks. Breaks the hydrogen bonds between bases.

Single strand binding protein

Binds to and stabilizes single-stranded DNA until it is used as a template

Topoisomerase

Relieves the strain from the DNA being so wound up. Does this ahead of the replication forks by breaking, swiveling, and rejoining DNA strands

Primase

Synthesizes an RNA primer at 5’ end end of each leading strand and at the 5’ end of each Okazaki fragment of the lagging strand

DNA polymerase 3

using parental DNAS as a template, it synthesizes new DNA strand by adding nucleotides to an RNA primer

DNA polymerase 1

removes the RNA nucleotides/primer from the 5’ end and replaces them with DNA nucleotides added to the 3’ end of the adjacent fragment

Ligase

joins the DNA together where there are gaps due to Okazaki fragments or primer. Forms a phosphoesterlinkage

Leading Strand

Where you are able to add DNA to the 3’ end. 3’ is toward the replication fork

Lagging strand

Where you would have to add DNA to the 5’ end. 5’ is closest to the replication fork. must use Okazaki fragments

What replaces incorrect nucleotides in the DNA

DNA polymerase

mismatch repair

repair enzymes correct errors in base pairing

nucleotide excision repair

nuclease cuts out the incorrect segment. then DNA polymerase lays down new DNA

mutation

sequence changes that become permanent and passed down to the next generation

sticky end of DNA

the part of the DNA in which it is too short for DNA polymerase to lay down new matching pairs. This leads to one end sticking out

telomere

the end of the DNA. super long so that no genetic information is cut off in the sticky ends

telomerase

cuts off the sticky end of DNA

histone

a tailed protein. a group of 8 histones get wrapped in 2 strands of DNA

What acts as markers on the DNA to where genetic information is

acetyl groups

Epigenetics

Changes in gene expression or phenotype that occur without altering the underlying DNA sequence.

What hypothesis did Garrod come up with?

1903. suggested that genes dictate phenotypes through the synthesis of particular enzymes.

what did beadle and tatum discover?

1 gene leads to 1 enzyme.

how did beadle and tatum discover their conclusion?

using cells that would turn into bread mold, they hit them with x-rays (no particular order just hit parts of the DNA with x-rays). the surviving cells then were tested to see what supplements were required for them to grow mold. this allowed them to see that certain enzymes were missing after the DNA was hit.

transcription

reading DNA to make RNA. creates mRNA

translation

creating proteins from RNA. created in ribsomes

what happens in eukaryotes but not in prokaryotes in terms of DNA expression?

post-transcirtional modification and post-translational modification

codon

a set of 3 bases that correlate with an amino acid

the start codon

AUG (methoionine)

the stop codon

UAA, UAG, or UGA

what does RNA polymerase do?

opens up the DNA and bind to a single strand. Reads the DNA and produces the appropriate base

what strand of DNA does the RNA polymerase read?

the RNA strand needs to start with 5’ and be adding to the 3’ end. Must choose the DNA that is opposite to that.

promoter

A specific DNA sequence where RNA polymerase binds and initiates transcription

transcription factors

mediate binding of RNA polymerase and initiation of transcription

what are the 2 common promoter boxes?

TATA and CAT

transcription initiation complex

transcription factors plus RNA polymerase

endonuclease

chop up single stranded nucleic acids in the cytoplasm (to help prevent bacteria replication)

polyadynlation sequence

a sequence of AAA …on the end of an RNA. this poly-A tail doubles over to make RNA look double stranded

5’ cap

added to 5’ end of RNA. a modified guanine nucleotide

introns

noncoding regions. get cut out (most of the time)

exons

coding regions that are then expressed in amino acid sequence

RNA splicing

done by spliceosomes. cut introns out and put together all the exons

tRNA

transfer RNA. brings the correct amino acid to the rRNA to build polypeptide chain

rRNA

ribosomal RNA. has 3 sites E,P,A. where the polypetide chain is created

anticodons

found at the bottom of tRNA. are the opposite of the protein attached (so that it can bind on the correct mRNA sequence)

what order does the tRNA follow in the rRNA

complex: A → P → E

how does the new amine group bind to the polypeptide chain?

the amine group from the new tRNA binds to the carboxyl group of the last peptide on the chain. done through a dehydration reaction

how do antibiotics work?

through blocking the attachment of tRNA to mRNA, meaning no proteins are formed from the bacterias DNA

post-transcriptional modification

splicing introns and exons

wobble

some tRNA doesnt have to have all 3 of the correct base pairings because there are multiple sequeences that code for the same protein

what happens when the stop codon is read by the tRNA

a release factor comes into the rRNA. then tRNA and polypeptides are released. then the ribosomal subunits disassociate (small and large) along with the mRNA

upstream

Toward the 5’ end of an RNA transcript, moving opposite to the direction of transcription

downstream

which is toward the 3’ end. in direction of transcription

how to make tRNA

a amino-acyl synthetase combines tRNA and the amino acid. the enzyme uses ATP to catalyze covalent bonding

signal peptide

tells cells where to send proteins in the cell

post translational modification

Chemical modifications made to a polypeptide or protein after translation, such as folding, cleavage, or the addition of chemical groups, necessary to make it functional.

polyribsomes

when multiple ribosomes are put on mRNA in order to produce proteins faster

point mutations

just one nucleotide base pair is incorrect

nucleotide pair substitution mutation

replaces 1 nucleotide with its pair (essentially flips the base pair upside down in comparison to what it should be)

silent mutation

has no effect on the genetic code

missense mutation

codes for the wrong amino acid

nonsense mutation

changes an amino acid to a stop codon (these types of mutations usually lead to death)

insertion mutation

addition of nucleotide base pair

deletion mutation

loss of a nucleotide base pair

frameshift mutation

insertion/deletion leads to the reading frame altered

mutagen

physical or chemical agents that can cause mutations

mitosis

process of cell division in which genetic material doubles and then splits

meiosis

division of reproductive cells. new cells only have half the genetic information

cytokinesis

division of the cytoplasm

karyokinesis

division of the nucleus

somatic cells

non reproductive cells that have 2 sets of chromosomes

gametes

reproductive cells that have half as many chromosomes as somatic cells (1 set)

centromere

holds chromatids together in the middle

mitotic phase

mitosis and cytokinesis

interphase

G1, S, G2

genome

all the DNA in a cell

how does a cell prep for cell division?

DNA is replicated and the chromosomes condense

prophase

1st phase of mitosis. chromosomes condense

prometaphase

second phase of mitosis. nuclear envelope starts to break down

metaphase

third step of mitosis. the chromosomes get lined up on the equator of the cell

anaphase

fourth step of mitosis. the sister chromosomes get pulled apart to form daughter chromosomes

telophase

the fifth and final step of mitosis. the cleavage furrow starts to form and DNA uncondenses.

how do microtubules work?

they are strings of amino acids that connect to the centromeres, then a motor protein pulls the chromatid away from the cell mid line. afterwards the microtubules are broken down to monomers