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building block of nucleic acid
nucleotide
what is nucleotide composed of
phosphate group, pentose sugar, nitrogenous base
what bases does DNA contain
adenine, guanine, cytosine, thymine
what bases does RNA contain
adenine, guanine, cytosine, uracil
is dna or rna single stranded
rna
is dna or rna double stranded
dna
what sugar does dna contian
deoxyribose
what sugar does rna contain
ribose
hershey and chase experiment
used radioisotopes to label T2 bacteriophage either internally or externally, determined which part of the virus contained the instructions for infection, realized only thing being transmitted between virus and bacterium is the stuff inside-genetic material makes up the virus
what does the condensation reaction form in the backbone of the dna
phosphodiester (covalent) bond between 3' carbon (OH) and 5' carbon(PO4)
which direction is the backbone of the dna assembled
5' to 3' direction - creates alternating phosphate/sugar backbone
how is the double strand of dna held together
hydrogen bonds
what direction is the double strand of dna formed in
anti parallel
purines (double ring structure) pair with
pyrimidines (single ring structure)
purines are
adenine and guanine
pyrimidines are
cytosine and thymine
adenine with
thymine
guanine with
cytosine
triple bond between which pair in dna
cytosine and guanine
double bond between which pair in dna
adenine with thymine
in formation of chromosomes, dna is supercoiled with several proteins that are called
histones
structures formed when dna is coiled with proteins in formation of a histone is called
nucleosomes
what do nucleosomes consist of
two molecules each of four histone proteins (an octomer)
why is dna attracted to histones?
dna is negatively charged
steps of making a chromosome
starts with histone
dna wraps around octomer
dna associated with octomer (protein) =nucleosomes
series of nucleosomes=chromosome -fiber formed from groups of nucleosomes =chromatid 5)H1 histone locks spool in place, can't unwind
further histone association occurs outside nucleosome with connection of H1 histone protein
histone is
protein whose primary purpose is to associate itself with dna
octomer is
8 little histone proteins
how much of the human dna actually codes for proteins
less than 2%
what percentage of the dna is unique for every person
98%
what percentage is known as genes
2%
majority of dna is composed of what type of sequences
repetitive
what are the two types of dna repetitive sequences
HRS, STR
HRS (highly repetitive sequences)
unique, no coding function, 5-300 bases in length
STR (short tandem repeats)
(ex. GAGGAGGAGGAG) used for dna profiling, unique regions: polymorphisms ,2-5 bases in length, inherited
unique regions on STR are called
polymorphisms
how many places (loci) will have polymorphisms
13 - look at these to match sample tissues
how much of 2% helps to form the structure of the DNA around a centimeter-called structural dna
20%
what is necessary during cell division to double the quantity of DNA
replication of DNA
what does dna replication involve
enzymes, free nucleotides
what type of process is dna replication
semi-conservative
what experiment confirmed semi-conservative process
meselson stahl
what does semi-conservative process mean
when you make new pairs of DNA, you conserve half the strand into the new stand
5 steps to dna replication summary
unzipping dna strand
initiation of new strand
elongation of growing strand
the lagging strand
completion
step one of dna replication involves which enzyme
helicase bc it breaks down the hydrogen bonds between nitrogenous bases to expose these new bases to new pairs- unzips the dna (zipper starts at the replication fork) , identifies strands (depends on direction)
in dna replication how are new strands built (what direction)
5'-3' , so there there is an exposed 3' carbon, and bc of condensation reaction there is a hydroxl group on 3' end (can add another group and form water)
in dna replication what way is leading strand and what direction is new strand
leading is 3'-5' and new is 5' to 3'
what enzyme is involved in step two of dna replication
primase
what does primase do in step two of dna replication
adds a short sequence of RNA (5-10 nucleotides) called a primer at the replication fork, tells the action where to start
what enzyme is involved in step three of dna replication
dna polymerase III
what does dna polymerase III do in step three of dna replication
adds nucleotides in a 5' to 3' direction, nucleotides originate as dNTP molecules, two phosphate groups used as energy source to join nucleotide to complementary base, looks for primer, recognizes it and gets the complementary bases in 5'-3' direction
what enzymes are involved in step 4 of dna replication
primase, DNA pol III, dna ligase
replication occurs
continuously on parental strand
replication occurs in fragments called
ozaki fragments
DNA pol III adds
new dNTPs to the strand, waits until there are bases exposed, brings "chunks" together
in 4th step of dna replication, what does DNA ligase do
joins fragments brought by DNA pol III, once ozaki fragment is placed- joins two fragments together
what enzyme is involved in step 5 of dna replication
DNA pol I
what does DNA pol I do in 4th step of dna replication
removes the original RNA primer and replaces it with DNA nucleotides/bases (bc the primer is ran based) , spot checks for errors
what is transcription
process of synthesizing a complementary rna strand using dna as a template, copies stuff that is important, not transcribing the 2% anyways
what is rna used for in transcription
primary enzyme (RNAP), used to create the preRNA strand
transcription makes a single strand of rna that can
leave the cell and transmit the code
why does transcription only transcribe genes?
genes are the only things that mean anything
steps of transcription
rna poly searches dna strand for a coded region known as promoter
rna poly binds to promoter and begins to unzip 2 dna strands
rna poly also brings complementary NTPs to bind with only one of the DNA strands (known as the antisense strand)
transcription continues until the terminator is reached- indicates the completion of the transcription and causes the newly sequenced RNA to detach
diagramming in transcription uses a promoter called a
TATA box that tells RNA pol to bind there- will bind, break bases, and pulls in corresponding RNA nucleotides
strand used as a template in diagramming in transcription
antisense strand
other strand in diagramming in transcription is called
sense strand
sense strand in diagramming does what in transcription
gives the message
what is the terminator in diagramming in transcription
tells transcription to stop
rna strand in diagramming in transcription
same as the sense strand except all Ts are replaced by Us ( no thymine in RNA), this is the message but the sense strand is also the message
within protein coding regions in post-transcription modification there are stretches of non-coding DNA called what
introns
in post transcription modification the initial rna strand that is formed contains both
introns and exons (expressed sequences)
in post- transcription modification what are specialized enzymes that cut the non coding regions
splicosomes
what is added to the 5' end in post-transcription modification
cap (guanine)
what is added to the 3' end in post-transcription modification
poly -A tail (adenine)
why is the cap and the poly-a tail added to the new mRNA in post-transcription modification
provides some protection
every protein begins with what sequence (post-transcription modification)
AUG (won't start until this sequence is read)
CH3 is what group
methyl
appears that dna that is inactive is also what
highly methylated (meaning that methyl groups have been added) - like barr bodies
transcription factors
proteins that assist with gene expression by binding the RNA poly to the promoter
transcription activators
proteins which cause looping of dna to shorten the distance to the next promoter
repressors
proteins that bind to dna segments called silencers to block transcription
environment can also
play a role in a number of genes that are expressed (areas of pollution)
translation
the process by which a mRNA molecule is used to determine the sequences of amino acids found in a protein... takes place of ribosomes.... to be continued
ribosome consists of
two subunits (large and small)
each subunit of ribosome is composed of
rRNA and proteins, constructed in the nucleus
between the two subunits of a ribosome there are
binding sits for mRNA and three sites for the binding of tRNA ( A and P and E sites)
the A site between the two subunits of a ribosomes does what
holds the tRNA carrying the next amino acid
the P site between the two subunits of a ribosomes does what
holds the tRNA carrying the growing chain
the E site between the two subunits of a ribosome does what
site from which the tRNA has lost its amino acid and is discharged (e= exit)
all three types of rna work together to form
polypeptide
how is mra read
in a 5' to 3' direction as a series of codons (triplet bases)
first codon bases will enter on 5' end with GGG cap
looking for start codon - AUG
64 possible combinations (4 RNA bases)
20 amino acids
lots of redundancy - degenerate
the tRNA molecule will move...
sequentially through the three binding sites from A to P to E (exit)
tRNA or transfer RNA is
a nucleic acid with 5' to 3' end 3' end has a base sequence CCA which is where the amino acid will attach folder "clover leaf" structure due to hydrogen bonds that occur between parts of the single strand on one of the loops of clover there is an anticodon unique to each tRNA which will pair with specific mRNA codon activated when amino acid is attached
four phases of translation
initiation, elongation, translocation, termination
initiation stage of translation begins with
start codon AUG which is found on 5' end of the mRNA
during initiation each codon will
attach to a particular tRNA molecule with the exception of the 3 stop codons (61 with amino acids), this attachment is facilitated by an enzyme specific to each amino acid and requires energy,
once the amino acid attaches to the tRNA in initiation of translation the structure is
activated and combines with the large ribosomal subunit and forms the translation initiation complex
elongation
more tRNAs will bring amino acids to the mRNA ribosomal complex, elongation factors provide assistance in joining tRNAs to the mRNA at the A site, the initiator tRNA moves to the P site and peptide bonds are formed between amino acids
translocation in translation begins when
during elongation
what is translocation
the movement of one tRNA from one site to another adding the amino acid to the growing chain, as the tRNA moves from the A site to the Psite it transfers the polypeptide chain to the new tRNA which enters exposed A site
when does termination begin
with one of the three stop codons
Note
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