Molecular Genetics - Till Midunit Flashcards
What are the instructions in an organism’s DNA do
Provide the direction to build the proteins the organism requires
What is DNA responsible for ensuring
genetic continuity
What is specific about chromosomes when it comes to different species
Size and number of chromosomes
What is the name of the plant with the most chromosomes
The Adder’s Tongue Fern
What are the three steps that need to occur to go from a gene (DNA) to a polypeptide
Portion of DNA that codes for a protein is activated, the nucleotide sequence is transcribed into a molecule of RNA which then moves to the cytosol where its sequence is translated by ribosomes into polypeptides
Where is DNA stored in Eukaryotes
The nucleus
Where is DNA stored in prokaryotes
The nucleoid region
What are genes
Genes are the coding regions of DNA which contain the instructions to build proteins responsible for each trait
What are alleles
Versions of each gene that give a trait more than 1 potential physical appearance
How do eukaryotes pack all of their DNA into a cell
A DNA strand is wrapped around 8 alkaline histone proteins and they are held together by positive and negative charges. It coils up to protect itself and fit
What is a genome
A genome is the complete set of an organisms hereditary material
What is the size of a human genome
3 billion base pairs
How many genes do humans have
20-25000
What functional group is associated with the 3’ Carbon
Hydroxyl group
What functional group is associated with the 5’ Carbon
Phosphate group
What is the orientation that the strands of DNA run in
Anti parallel
What is the distance between each base pair
0.34 nanometers
What way does the double helix turn
Clockwise
What is the size of one complete turn of the double helix of DNA
3.4 nanometers (10 base pairs)
What are the complimentary base pairs
Adenine - Thymine
Guanine - Cytosine
How many hydrogen bonds does the G-C base pair create
3 Hydrogen Bonds
How many hydrogen bonds does the A-T base pair create
2 Hydrogen Bonds
What is the bond that connects the sugar and base in a nucleotide
Glycosyl Bond
When a lot of crossing over occurs, what happens to the distance between two genes
They get farther apart
What did Gregor Mendel do
Carried out genetic experiments with pea plants and then published his work on the principles of genetics (called them factors at the time)
What did Fredrich Miescher do
Isolated a substance from the nucleus of white blood cells which he called nuclein (now known as DNA)
What did Sutton and Boveri do
Proposed the chromosome theory of heredity. They both independently realized that the factors mendel talked about were on the chromosomes
What did Thomas Morgan Hunt do
Morgan was skeptic of the Sutton Boveri theory, however he then identified the first X-Linked gene in fruit flies showing that a trait could be linked to the sex of the fly supporting Sutton and Boveri’s theory
After proving sex-linked traits, what did Morgan do
Described Gene linkage where genes on the same chromosomes are linked together
What did Alfred Sturtevant do
He was a student in Morgan’s lab who created the first gene map
What does crossing over do
Brings new phenotypes
What is an example of gene linkage
Blue eyes and blonde hair on the same chromosome
What did Griffith discover in his mouse disease experiment
Dead cells’ pathogenic properties could be passed on to living bacterial cells, this was the accidental “Transforming Principle”
As Griffith passed away in an air raid during WWII, who carried on with his work
Avery and his team were the first to demonstrate that the transforming principle was likely DNA, This experiment was not conclusive as it was a negative experiment
Who provided conclusive evidence to say that DNA was the genetic material
Hershey and Chase did a radioactive DNA experiment where they took radioactive DNA and Radioactive Protein and added them to samples of E-Coli, this was conclusive that DNA was the genetic material INSTEAD of protein
Why was Avery and his team hesitant to report their findings
At the time it was believed that protein were the genetic material
What did Joachim Hammerling prove
Used Green alga (Acetabularia) and determined that its genetic information was store in the nucleus containing foot which meant that the nucleus contained the hereditary material. He did this by cutting the alga to the foot, and saw that it regenerated a copy of the stalk and cap to its original state
What did Chargaff propose
Chargaff’s Rules stated that A=T and C=G, and that the complimentary pairs occured in the same ratios,
Adenine = x% and Thymine = x%, Guanine = y% and Cytosine = y%
What did Franklin and Wilkins do
Used X-Ray crystollography to show the shape of DNA
What was Franklin’s main acompolishment
Photo 51 which shows the x-ray diffraction pattern of a DNA molecule which provides info about the position of atoms in DNA (Equal spaces between rings)
What conclusion did Watson and Crick reach after seeing this image and reading Franklin’s report unethically
It was a double helix that had two antiparallel backbones on the outside with bases inside
What was Linus Pauling in the hunt for DNA exploration
He was a well known nobel prize winner in the states who was giving competition to those overseas, however his proposal of a triple helix was wrong
What was unethical about Maurice Wilkins
Showed watson and crick photo 51 without telling franklin
What were the three proposed mechanisms of DNA replication
Conservative replication (lots of bonds breaking and forming), Semi conservative (what actually happens), and Dispersive replication (regions of DNA interspersed with new DNA)
After mitosis, 2 daughter cells end up with the same sets of chromosomes what does this mean and when does it occur
Means that DNA must replicate, occurs in the S Phase of Interphase
What did Meselson’s and Stahl’s experiment say
Nitrogen is found in DNA, they grew e coli bacteria in a heavy isotope and then switched to a light isotope then used the density gradient centrifugation, cesium chloride was used. This allowed them to use this technique to predict and then test the results of DNA replication that semi conservative was the actual method of replication
What type of replication did Watson and Crick propose
Semi conservative
What happens before DNA replication to start it up
when proteins bind to the origin of replication, only one ori in prokaryotes but many in eukaryotes
What are the two reasons that eukaryotes have many origins of replication
The DNA cannot be completely unwound because it would be too big to fit in the cell, it would also take far too long to replicate the 3 billion base pairs of human genome (700 days)
What happens in the first step of DNA replication
DNA helicase breaks the bonds between complementary base pairs making them linear, single stranded binding proteins bind to the linear pairs preventing reannealing, DNA gyrase then relieves the tension created by unwinding the strands and cutting them
What is the second step of DNA replication and what happens
Elongation is when replication starts in 2 different directions from each origin, the replication fork is the area where enzymes that are replicating DNA are bound to ssDNA, there is a replication fork at each end of a replication bubble
After the replication bubble is created, what happens
A RNA primer (10-60 base pairs) is put on by the enzyme primase because DNA polymerase III, the enzyme that synthesizes DNA 5’ to 3’ can only add nucleotides to a free 3’ end.
Where does Energy for elongation come from
Deoxyribonucleoside triphosphates
What is the leading strand
The top strand of DNA going from 5’ to 3’ built continuously toward the replication fork with only one RNA primer at the 3’ end
What is the lagging strand
The bottom strand of DNA from 5’ to 3’, but on the opposite sides as the Leading strand, and this is built discontinuously away from the replication fork with multiple RNA primers
What does DNA Polymerase I do
excises the RNA primers and replaces them with appropriate DNA strands
What happens after the excising of the RNA primers
DNA ligase joins the okazaki fragments by phosphodiester bonds to get rid of the gaps
Without proofreading, what is the chance for a DNA replication error
1 in 10 000 base pairs
What does the proofreading
DNA polymerase I and III act as an exonuclease which removes nucleic acids to fix incorrect base pairing (excises)
After proof reading, what is the chance for DNA replication error
1 in 1 billion base pairs
Why is prokaryotic DNA found in the nucleoid region
There is no nucleus
What is the shape of prokaryotic DNA
The ends of DNA bind to form closed circular DNA loops which fold on themselves becoming supercoiled DNA
In addition to the super coiled DNA, what other DNA molecules exist in prokaryotes
There are often other circular DNA molecules found in prokaryotes called plasmids where antibiotic resistance genes can usually be found
What are characteristics of plasmids
They can be copied and transmitted between cells which is why antibiotic resistance can spread in bacteria
What do plasmids help humans with in today’s world
Genetic engineering/biotechnology
Do Eukaryotes also have supercoiled DNA
they do have supercoiled DNA, but it is not that important compared to that of the prokaryotes
What is the length of one human genome
1.8m (6 billion base pairs, 3 billion from each parent)
What are the constituents of chromosomes
5% RNA, 35% DNA, and 60% Protein
What does DNA wrap around
8 Alkaline histone proteins to create a nucleosome
What is a nucleosome
The bead-like structural unit of chromosomes composed of acidic DNA (200 base pairs) with a negative charge that are wrapped twice around a cluster of 8 alkaline histone proteins with a positive charge, opposites attract
What percentage of the human genome is non coding
around 95%
How do you compare the genomes of different individuals?
By their non coding regions
What are non coding regions filled with
Variable number tandem repeats which are sequences of base pairs that are repeated over and over again
What about the VNTR’s varies between individuals
The length of the base pair sequences, and the position of the repeating segment in the genome
Can VNTR’s also be found in genes
Some VNTR’s on occasion can be found in the genes (coding regions)
What are the ends of chromosomes made of, and what name are the ends given
The ends of chromosomes are made of long sequences of non coding DNA known as telomeres
What is the main role of telomeres
Critical to preventing cells from losing valuable genomic material during DNA replication
What would happen if DNA Gyrase was not available during DNA replication
The strands would not be able to relieve the tension created by the Helicase untwisting and so this could destabilize the strand and may also prevent the binding of other enzymes
Given histones, solenoids, nucleosomes and Chromosomes, arrange them from smallest to largest in terms of molecule size
Histones, Nucleosomes, Solenoids, and Chromosomes
When the RNA primer is removed from both daughter strands’ 5’ end, what happens
There becomes no adjacent nucleotide chain with a free 3’ end that can be extended to fill the gap and so no enzyme works in the 3’ to 5’ direction. Not only are their gaps on the daughter strands, the corresponding parent segments end up breaking off because the complementary strands are left unpaired.
With each replication, what happens to the daughter strands
Each daughter strand becomes shorter than its parent, each time DNA is lost, the loss i approximately 100 base pairs
What is the hayflick limit
Also known as cellular senescence, this limit says that in humans, DNA can be passaged 50 times before it can’t replicate anymore
How big is the sequence of Telomeres
6 Base sequence repeated thousands of times
What is the erosion of telomers related to
Cell death
What does telomerase do
Extends the length of telomeres
What do cancer cells have a lot of
Telomerase allowing them to divide well beyond normal life span
To provide anti aging, what should be done to telomerase levels
Increase telomerase levels making cells and whole organism last longer, also an increased chance for cancer
To treat cancer, what should be done to telomerase levels
Decrease telomerase levels making cancer cells not live long, however it will make you age faster as it will effect all cells
What steps should be taken to maintain telomere length and increase telomerase levels in the human body
Less stress, excercising, good diet, and sleep
What does obesity cause
Shorter telomeres
Where is telomerase found
Stem cells and certain white blood cells
Can conclusions be made about telomere length and life span between different species
No direct conclusions can be made based on solely this factor
Where can full length telomeres be found
In germ cells, as those cells give rise to gametes
What does cell life depend on
Depends on rate of telomere erosion, not length of telomeres
Can shortening telomeres treat cancer
No, the underlying issue of heightened telomerase levels still exists and so it will just extend the telomeres again
what is the one gene one enzyme hypothesis
each gene is unique and codes for the synthesis of a single enzyme
what is the one gene one polypeptide hypothesis
each gene is unique and codes for the synthesis of a single polypeptide; the restated version of the one gene–one enzyme hypothesis
What is the central dogma
the fundamental principle of molecular genetics, which states that genetic information flows from DNA to RNA to proteins
What are the two main processes in the central dogma
Transcription and Translation
What is transcription
mechanism by which the information coded in nucleic acids of DNA is copied into the nucleic acids of RNA; something rewritten in the same language occurring in the nucleus
what is translation
mechanism by which the information coded in the nucleic acids of RNA is copied into the amino acids of proteins occurring in the cytoplasm
What are the three differences between RNA and DNA
DNA is double stranded while RNA is single, Adenine pairs with thymine in DNA and with Uracil in RNA, in DNA the sugar is deoxyribose and Ribose in RNA
what are the characteristics of mRNA
- varies in length, depending on the gene that has been copied
- acts as the intermediary between DNA and the ribosomes
- is translated into protein by ribosomes
- is the RNA version of the gene encoded by DNA
what are the characteristics of tRNA
- functions as the delivery system of amino acids to ribosomes as
they synthesize proteins - is very short, only 70 to 90 base pairs long
What allows mRNA to leave the nucleus after transcription
The pores in the nuclear membrane
