Unit 3: Molecular Genetics Flashcards
Who were credited with deducing the structure of DNA
James Watson and Francis Crick
What year was the DNA structure deduced
1953
3 main components of DNA
- A deoxyribose sugar
- A phosphate group
- A nitrogenous base
DNA is a what
Nucleotide polymer
What is DNA structure like
- Thread like
- it is twisted in a clockwise direction to form a double helix
What direction does DNA strands run in
Consists of 2 anti parallel strands of nucleotide( run side by side in opposite direction)
Each DNA strand has what
5’ and 3’ end which run in opposite directions to one another
The 5’ end terminates with what
Phosphate group
The 3’ end terminates with what
Hydroxyl (OH) group of the sugar
What are the complementary nitrogenous base pairings
Adenine and thymine
Cytosine and guanine
What nitrogenous bases are purines
adenine and Guanine
What nitrogenous bases are pyrimidines
Cytosine and thymine
How long would s stretched out long double helix be
1.8m but an individual núcleos would be 5nano meter
Histones
8 stabilizing proteins
For every 200 nucleotides , DNA is what
Coiled around a group of 8 stabilizing proteins
What charge are histones
Positively
Nucleosomes
The complex of histones supporting coiled DNA
Chromatin fibre
A series of nucleosomes coiled
How is final chromosome structure obtained
Supercoiling of chromatin fibre
What are the 3 forces contributing to DNA molecule
- Phosphodiester Linkages
- Hydrogen bonding
- Hydrophilic/ hydrophobic reactions
Phosphodiester linkages
Link the sugar / phosphate of one nucleotide to another ( stabilizes the handrail)
Hydrogen bonding
Keeps the 2 strands together as well as stabilizing the inner core (rungs)
Hydrophilic/ hydrophobic reactions
Cause the bases (hydrophobic) to remain inside the structure while the phosphate group and group (hydrophilic ) face out into the watery nucleus of the cell
(Similar to the cell membrane )
Senescent cell
larger than young cells, excrete proteins at a different rate and no longer divide.
telomerase
enzyme that appears to stabilize telomere length and keep cells useful
telomeres
chromosome tips and they consist of thousands of identical secions of DNA strung together like beads of a neckalce.
which type of cells seem to have a supply of telomerase
cancer cells and stem cells
the link between telomerees and aging has been supproted by what evidence
by studying people with progeria who are born with short telomeres and have an average lifespan of 12,7 yrs
why might cell senescence have evolved
to keep us tumor free during our reproductive years
Watson and crick discovery
credited with deducing the structure of DNA (double helix) in 1953
Rosalind Franklin
- suggested that the sugar phosphate backbone of DNA faced the outside of the molecule and not the inside
- suggested DNA was a double helix
- determined the diameter of DNA moleucle
Alfred Hershey and Matha chase
- confirmed that the DNA of a bacteriophage transformed the DNA of an infected bacterium
Avery, Mccarty, and mcleod
showed that DNA rather than RNA or protein, was the transforming substance
Chargaff
discovered that the nitrogenous bases in DNA always occur in exact ratios, with the number of adenine matching the number of thymine, and the number of cytosine matching the number of guanine
Hammerling
the nucleus of a cell contains hereditary info that controls the development of organisms
Griffith
discovered a substance derived from infectious bacteria that could turn non-infectious bacteria into infectous bacteria
Miescher
“nuclein” - DNA
what did melseson and stahl discver and what is it known as
proof of semiconservative replication aka “the msot beautiful experiment on earth”
what did meselson and stahl do to discover what they did
- grew Ecoli bacteria in a nutrient medum rich in 15N for several generations to ensure that the 15N would be encorporated in the DNA.
- bacteria were then transfered to a culture medium containing the light isotope 14N
- centrifugation was used to isolate the DNA strands
- cetrifugation was centrifugal force and boyant forces to seperate materials of diffeent densities
what was in test tube 1 , 2, 3 , 4 and what did they prove
TEST TUBE 1: containing heavy DNA - produce one discrete bond in a low region
TEST TUBE 2: Containin regular DNA- produce one discrete bond in a higher region
TEST TUBE 3: Bacteria from heavy N medium allowed to replicate once in the normal N medium - produced an discrete bond intermediate between the bonds in tube 1 and 2
- PROVED THAT DNA WAS A HYBRID(combined one heavy and one regular strand)
TEST TUBE 4: Bacteria from hevy n medium allowed to replciate twide in the normal nitogen medium - produced 2 discrete bonds: one at at the intermediate level and one at regular N level
- PROVED THAT THE INITIAL DNA WAS CONTINUALLY USED AS A TEMPLATE
what type of replication is DNA
semi-conservative
what is each new DNA strand composed of
an existing parent half and newly synthesized half combined together
what do proteins bind to on DNA
replicated origins
DNA helicase
breaks the hydrogen bond holding the two complementary parents together. Resulting in an unzipped helix that terminates at the replication fork
Single stranded binding proteins
- keep the DNA strands seperated by blocking reformation of hydrogen bonds
DNA gyrase and Topoisomerase
relieves tension and unwinds double helix
what does DNA polymerase III do
builds the complementary strand
what direction does DNA polymerase synthesize DNA in
5’ to 3’ direction
leading strand
strand which uses the 3’ to 5’ direction template strand and synthesized continuosly(5’to3’) in the direction of the replication fork
lagging strand
strand which uses the 5’ to 3’ template strand and is synthesized discontinuosly (5’ to 3’) in short fragments called okazaki fragments in the opposite direction of the replication fork
DNA polymerase 1
removes RNA primers from the leading strand and fragments of the lagging strand and replaces them with the correct deoxribonucleotide
DNA ligase
joins the okazaki fragments together via phosphodiester bonds.
termination of DNA rep
as strands are built, they automatically rewind to form a double helix
how does DNA rep ensure accuracy
- DNA polymerase III and I can recognize whether hydrogen bonding has taken place between base pairs, if not , a mismatch has occurred and the polymerase excises the incorrect base and inserts the correct one
telomeres
- long sequences of repetitive non coding DNA
- buffer zones at the ends of chromosomes that help guard against the loss of valuable genetic material during replication.
DNA in comparison to RNA
- SUGAR: DNA has deoxyribose and RNA has ribose
- STRUCTURE: DNA has double helix and RNA has single helix
- SIZE: DNA is a larger molecule that can be thousands of nucleotides long while RNA is a smaller molecule that transcribed only a section of DNA
-AMOUNT: DNA is few molecule in the cell and RNA is many molecules in the cell - WHERE: DNA in nucleus and RNA in both nucleus and cytoplasm
-KINDS: DNA has one type and RNA has three types (mRNA,tRNA and rRNA)
-NITROGENOUS BASES: DNA- A,C,G,T while RNA- A,C,G,U
genes
a sequence of nucleotides in DNA or RNA that encodes the synthesis of a protein
genes are not what
spaced regularly along chromosomes
size of genome and number of genes is?
Not directly related
Exons
coding regions
Introns
noncoding regions
In general, the frequency and length of introns is loosely related to
the development complexity of the organism
In vertebrates what percentage of introns we have
95% non coding regions
multigene family
- contain from a few hundred up to hundred of thousands of copies of the same or very similar genes
- in some cases they code for a high in demand protein
triplet hypothesis
genetic code codons are made up of nucleotide triplets - Francis crick
genetic code central dogma
the genetic code reveals the amino acid that each codon (nucleotide triplets/3 letters) codes for
characteristics of genetic code
- continuity - reads as a set of 3 letter codons with no spaces and has a correct reading frame
- redundancy- 64 possible codons but only 20 amino acids
- offers some protection against mutation
- not random - Universality- genetic code is essentially the same in all living organisms(ie. same mRNA codons correspond to the same amino acids)
- provides evidence that most organisms share a common ancestor
1 protein has
hundreds of amino acids
the sequene of amino acids is determined by
the sequene of nucleotides in an organism
a protein is composed of combinations of
20 amino acids
3 types of RNA
mRNA- messenger RNA
tRNA- transfer RNA
rRNA- ribosomal RNA
rRNA
provide the site on the ribosome where the polypeptide is assembled
tRNA
- smaller than rRNA
- there are a max number of the kinds of tRNA, though may vary from organism to organism
- float freely in cytoplasm
- transport amino acids to the ribosome and position amino acids on the chain
mRNA
- long single strand of RNA
- passes from nucleus to cytoplasm through nuclear pores
- brings info from chromosomes to ribosomes to direct protein synthesis
-spliced, capped and tailed before leaving nucleus
2 main processes in protein syntheis
Transcription
Translation
transcription
- RNA copy of a gene is produced (mRNA) which is transcribed from DNA
- ## this is initiated when the enzyme RNA polymerase binds to a sequence of nucleotides on one DNA strand
translation
- synthesis of polypeptides by a ribosome
- information of mRNA directs the choice of amino acids
- ribosomes moves along in step 3(codons)
DNA to mRNA
transciption
4 stages of transcription in DNA to mRNA
- Initiation
- Elongation
- Termination
- Processing of mRNA transcript
a)capping and tailing
b) splicing
Initiation in transcription
- RNA polymerase contains a binding site that only recognizes a promoter sequence on the DNA
promoter sequence
- rich in A and T nucleotides
- sequences are not palindromic so RNA polymerase will bind in only one orientation
- this sequence does not get transcribed only serves as the attachment site for RNA polymerase
- Elongation in transcription
- RNA polymerase works in the 5’ to 3’ direction
- Does not require a primer to begin
- transcribes only one strand( template strand)
- RNA polymerase opens the helix one section at a time and arranges the correct RNA nucleotides according to the DNA template
- Once the RNA polymerase passes a given point the DNA helix reforms and the mRNA strand seperates from the DNA
- RNA polymerase no proofreading capability
- Termination in transcription
- transcription stops when RNA polymerase encounters a terminator sequence (highly specific)
- processing of mRNA transcript a)capping and tailing
- 5’ cap- made of modified guanine nucleotides which is added to the start of the primary transcript(pre-cursor mRNA)
- Poly A tail- string of 200 adenine ribonucleotides is added to the 3’end by poly A polymerase
- both addition protect the mRNA from digestion by enzymes and assist in the initiation of translation
- processing of mRNA transcript b) splicing
- eukaryotic genes contain exons and introns
- spliceosome cut out introns and join exons together to create a continuous coding regions on the mRNA transcript
From mRNA to protein
translation
5 sidesteps of translation
- ribosomes
- transfer RNA
- initiation
- elongation(of polypeptide)
5.termination
ribosomes in translation
- ribosomes consists of 2 subunits (1 large and 1 small) and rRNA
- 2 subunits bind mRNA between them
- moves along the mRNA transcript in the 5’ to 3’ direction
tRNA in translation
- tRNA is a small single stranded RNA with a 3 lobed stercutre resembling a clover leaf
- anti codonregion- contains a nucleotide triplets complementary to a codon on mRNA
- amino acid attachment site - across from anticodon region where the appropriate amino acid bonds
- aminoacyl tRNA- a tRNA bound to its particular amino acid
3.initiation in translation
- 1st tRNA is brought into the P(peptide) site carrying methionine since it corresponds to the start codon AUG
- 2nd tRNA enters the A(acceptor) site
- Elongation of polypeptide in translation
- A peptide bond is formed between the 2 adj amino acids
- the ribosomes translocates (shifts) one codon over to the 5’ to 3’ direction and the next tRNA enters the A site
- process is repeated until a stop codon is reached ( a codon that does not code for an amino acid)
- termination in translation
- a release factor protein aids in dismantling the ribosome- mRNA complex releasing the polypeptide chain
- polypeptide chain may undergo further processing
- sugar (glycosylation) or phosphate(phosphorylation) may be added
- polypeptyide may be cleaved
- 2 or more polypeptides may combine together
mutations
errors made in the DNA sequence that can be inheritied or caused by the environment
silent mutation
A mutation that does not alter the resulting sequence
missense mutation
a mutation that changes a single amino acid in the coding sequence
nonsense mutation
a mutation that results in a premature stop codon
framshift mutation
a sifdt in the reading frame resulting in multiple missense and/or nonsense effect
point mutation
A change in a single nucleotide within a gene
substitution
the replacement of one base pair in a DNA sequence by another base pair
deletion
the removal of a base pair (small scale mutation) or larger coding regions(large scale mutation ) to a DNA sequence
translocation
the movement of entire genes or sequences of DNA from one chromosome to another
inversions
chromosomal segment that has reversed its orentation in the genome
transporable elements
jumping genes that can move from one location to another n the genome
proteins are produced in your body on the basis of
supply and demand
different proteins are needed at
different stages of your life, different time of the day and different cells of the body
all cells in your body contain the information (gene) for producing hemoglobin but
not all cells activate this gene
the LAC operon
- Ecoli produces the enzyme B-galactoidse, responsible for breaking down lactose only when latose is present
- the gene for B-galactosidase is part of an operon
- if lactose is not avaliable for the E.coli a repressor protein binds to the operator region making it impossible for RNA polymerase to bind to the promoter
- if lactose is present in some E.colis environment the cell will take up the lactose and some will bind to the repressor. xausin a conformational change in the repressor resulting in it detavching from the operator site- lactose acts as an inducer in this case
operon
a cluster of genes under the control of one promoter and one operator
operator
the region in the operon that regulatory factors
corresporessor
a signal molecule that binds to reduce the expression of an operons gene
repressor
a protein that binds to the operator to repress gene transcription
inducer
a signal molecule that triggers the expression of an operons gene
the TRP operon
- Trpytophan is an amino acid that is used by E.coli cells for the production of protein
- if concentration of tryptophan is high the genes for this amino acid production are no longer transcribed
- with high levels of tryptophan it binds it to TRP repressor protein , altering it’s shape so that it can now bind to the TRP operator
- Tryptophan is required to inactivate the trp-operon corepressor
gene expression regulation in eukaryotic cells
pretranscriptional control
transcriptional control
posttranscriptional control
translational control
post translational control
pre transcriptional control
- cells control the extent for which DNA is exposed to transcriptional enzymes 9the more condensed regions of DNA are not transcribed)
transcriptional control
the cells control whether or not exposed DNA is transcribed - involves regulatory proteins
post transcriptional control
cells controls the rates of processing of pre-mRNA into finished mRNA
- accomplished by not adding cap or tail
translational control
regulatory proteins can bind to 5’cap of the molecule preventing the small ribosomal subunit from altering to the mRNA
post translational control
regulatory proteins may break down the polypeptide before ity is able to reach its destination
during prophase of meiosis homologous chromosomes
pair up forming a tetrad
crossing over is
the exchange of DNA between the 4 chromatids of a tetrad
linkage
- genes that are part of the same chromosome are said to be linked
- the degree of crossing over between 2 genes on a single chromosome is proportionate to the distance between them
mapping
- the frequency of crossovers in offspring can be used to map the relative position of the genes on the chromosome
- this method is called recombination mapping
- distance is measured in map units (m.u.)
the highest possible recombination frequency is
50%
if recombination occurs twice between 2 genes
then there is no recombination in the offsprings(only odd num of crossovers will show up in offspring)
HIV 1
first indentifed in 19812, evolved in chimps and jumped species to humans
HIV 2
first identified in 1985, less prevalent, less virulent form
a virus must be able to
make it past the bodys defense mechanisms
HIV is unique as it
invades the cell whose job it is to protect the body
with HIV you become
susbsceptible to infections our immune system could normally fight off
HIV infects what cell
helper T-cell
HIV is a what
Retrovirus - genetic information is in the form of RNA instrsad of DNA
retrovirus encodes a special virus called
reverse transcriptase
reverse transcriptase
coverts RNA into a complementary strand of DNA
HIV is very good at
mutating to avoid immune detection, it does this by changing the protein on the outside of its memebrane
