DNA Replication- lecture #18 Flashcards
what is non-disjunction?
homologous pairs fail to separate it normally leaves the other chromosome pairs distributed normally
when does non-disjunction occur?
when members of homologous pairs do not separate during meiosis I
when sister chromatids do not separate during meiosis II
when sister chromatids do not separate during meiosis II what is produced?
one gamete with 2 copies of the same chromosome and another gamete without a copy of the chromosome
what is aneuploidy?
a gamete with an abnormal chromosome number is used in fertilization
when a gamete is missing a chromosome what is that called? how many chromosomes will there be?
monosomic (zygote is 2n-1)
45 chromosomes
when a gamete has an extra chromosome what is that called? how many chromosomes will there be?
trisomic (zygote is 2n+1)
47 chromosomes
what happens when aneuploidy occurs in mitosis, if it occurs early in embryonic development?
then the abnormal chromosome number will be transmitted to a number of cells having a large scale effect
what is polyploidy?
more than 2 complete chromosome sets are present
what is polyploidy common in?
plants
when can triploidy (3n) occur?
when one of the gametes involved in fertilization has undergone a non-disjunction (fail to separate) of all chromosome pairs
normal in plants
when can tetraploidy (4n) occur?
when the diploid zygote completes S phase in preparation for mitotic division and doesn’t divide
how many chromosomes do you end up with in tetraploidy?
92 (46 x 2)
what are the 4 types of altered chromosome structure?
deletion, duplication, inversion, translocation
what occurs in deletion?
chromosomal fragments are lost (genes are missing)
ABCDE
ABCD
what occurs in duplication?
duplicated fragment reattaches to the sister chromatid
ABCDE
ABCBCDE
what happens if duplication occurs on a non-sister chromatid?
alleles may create non-duplicates
what occurs in inversion?
the broken fragment reattaches to the same chromosome backwards
results in serious consequences
ABCDE
ADCBE
what occurs in translocation?
the broken fragment reattaches to a non-homologous chromosome
ABCDE MNOPQ
MNOCDE ABPQ
how can deletion/duplication occur?
due to unequal size exchange during crossing over
what is a missense mutation?
DNA change that results in different amino acids being encoded at a particular position in the resulting protein
what is a silent mutation?
type of mutation in the coding region of a gene that doesn’t actually change the amino acid sequence of the protein that is made.
what can structural alteration of chromosomes cause?
severe disorders
when does down syndrome occur in respect to chromosomes?
affects chromosome number 21 (47 chromosomes)
called trisomy 21
how many kids does down syndrome affect?
1 in 700
down syndrome is considered a syndrome because there is a set of symptoms that arise, what are some symptoms?
Round face
Skin fold at inner corner of the eye
Flattened nose bridge
Small and irregular teeth
Heart defects
Short stature
Reduced life span
50% of a woman with down syndrome’s eggs will have 3 copies of chromosome 21, what is the chance her offspring will be affected?
50%
what happens when there’s aneuploidy on sex chromosomes?
less of an issue then when on autosomal chromosomes
what does XYY on the sex chromosome signify?
normal sex development, taller
what is trisomy X? what is the sex chromosome sequence and what are some side effects?
XXX
learning disabilities, taller, otherwise normal
what is turners syndrome?
X
sterile, immature sex organs, normal intelligence
what is klinefelter’s syndrome? what is the sex chromosome? what are some side effects?
XXY
small testicles, sterile, breast enlargement, decreased intelligence
what happens when you start taking artificial testosterone?
causes real testosterone to stop working as efficiently
what was crucial to the determination of DNA as the genetic material?
infection of bacterial cells with a virus
what was originally thought to be genetic material?
DNA or protein
what happened when the pathogenic strain (disease causing bacteria) was treated with heat? griffith (1928)
heat killed
what happened when the remaining cellular material from the pathogenic strain was mixed with the non- pathogenic bacteria?
transformed non-pathogenic into pathogenic (disease causing bacteria)
what does the term transformation mean to Griffith?
naked DNA that you choose to put into your genetic binder
Avery isolated the heat killed bacteria and opened the cells, extracting the DNA, RNA and protein, what was the only thing that was able to transform heat killed bacterial cells into virulent cells?
DNA
what are bacteriophages (phages)?
viruses that infect bacterial cells
what is smaller, viruses or bacteria?
virus
what do bacteriophages (viruses) consist of?
DNA or RNA as genetic material (never both)
nucleic acid enclosed within a protein coat
obligate intracellular parasites
what did scientists Hershey and Chase want to know?
whether it was phage DNA or phage protein material with the ability for genetic material of the T2 bacteriophage
What did Hershey and Chase do to test if the DNA or protein was the genetic material of the T2 bacteriophage?
added a radioactive tag to the protein in one T2 batch (added the label to sulfur)
added a radioactive tag to the DNA in another T2 batch (added the label to phosphate)
what was left to be infected by the labeled DNA and labeled protein?
E. coli
How did Hershey and Chase prove that DNA was the genetic material of the T2 bacteriophage?
only the phage DNA was entering E. coli, protein was not
what are Chargaff’s rules?
The number of:
Adenine residues = the number of thymine residues
(adenine base pairs with thymine via 2 hydrogen bonds)
Guanine residues = the number of cytosine residues
(cytosine base pairs with guanine via 3 hydrogen bonds)
Composition of base pairs varies between species
what happens when a purine is paired with a pyrimidine?
3 rings across
what happens when a pyrimidine is paired with a purine?
3 rings across
why is the nucleotide sequence of the ladder random?
determines the genetic makeup of the individual
what is an example of composition base pairs varied between species?
bacteria vs eukaryotes
what is the structure of DNA?
2 strands come together (anti-parallel) to form a double helix
sugar phosphate backbone
why is the phosphate group of the negative phosphate sugar backbone found on the exterior?
minimizes repulsion
how many base pairs are there per full turn of the helix?
10 base pairs
a full turn of the helix is how long in length (nm)?
3.4nm
how far apart are bases (nm)?
0.34nm apart
what do hydrogen bonds do to the structure of DNA?
keep the DNA on equal distance apart
what has more thermostability, adenine + thymine or cytosine + guanine?
cytosine and guanine, because more heat is needed to break the bond
adenine and thymine are less thermostable
what is the net charge of the strand of DNA?
negative (-)
because the phosphate is negative and gives the backbone as well as the net charge of the strand a negative net charge
in order for DNA replication to occur what do the two strands need to do?
separate from one another
why is DNA replication classified as semi- conservative?
each parent strand (from original molecule) is paired with a daughter strand
conservative= parent strand
a pool of free nucleotides in the cell is used to synthesize what?
the new DNA strand
how are enzymes used in DNA replication?
enzymes are used to link the newly added nucleotides together
what are alternative models to the accepted semi-conservative model?
dispersive model
conservative model
what is the dispersive model?
all four strands consist of a mixture of new and old DNA
see picture in folder
what is the conservative model?
one double stranded DNA molecule is entirely newly synthesized DNA
one double stranded DNA molecule is entirely old DNA
what are some characteristics of E.coli?
single circular double stranded chromosome (bacteria)
4.6 million base pairs
can replicate in as little as 20 minutes
how many nucleotide pairs do humans have within 46 chromosomes?
6 billion
how often is an error made in nucleotide additions?
1 in every 10 billion
how long does it take in total to replicate?
around 3 hours (S phase of interphase)
what is the replisome?
more than 12 proteins and enzymes take part in DNA replication
is bacterial replication identical to eukaryotic replication?
essentially identical
what are origins of replication?
unique short nucleotide sequences
eukaryotic chromosomes may have 100s or origins of replication
what do initiator proteins do?
attach to the ori and open up the double stranded DNA molecule
what do initiator proteins do?
form a replication bubble
replication proceeds in both directions until what is completed?
entire double stranded molecule is completed
what is a replication fork?
they are included ahead of each bubble
how does the DNA unwind?
assistance of several proteins
what untwists the DNA at the replication fork?
helicase (it separates the two strands)
what do single stranded binding proteins (SSBP) do?
bind to separated strands and prevents them from reattaching
what does topoisomerase do?
an enzyme that breaks and rejoins the DNA strand upstream of where it is being twisted
what does RNA primer needed for?
needed to begin the process of DNA replication
what is RNA primer synthesized by?
primase (also known as RNA polymerize)
what does RNA primer do?
adds RNA nucleotides one at a time according to the DNA template
how will the new DNA strand begin, when using the RNA primer?
begin forming at the 3’ end of the RNA primer
what does DNA polymerase do?
catalyzes the addition of the new DNA by adding nucleotides one by one
there are many DNA polymerase, what DNA polymerase is most important?
DNA polymerase I and DNA polymerase III
why are the many DNA polymerase?
different affinity to add different nucleotides
DNA polymerase adds how many nucleotides per second in bacterial cells?
500 nucleotides/second in bacterial cells
DNA polymerase adds how many nucleotides per second in human cells?
50 nucleotides/second in bacterial cells
what is the starting nucleoside material in DNA replication?
nucleoside tri-phosphate
what is the difference between a triphosphate nucleoside and a triphosphate nucleotide?
after complete hydrolysis a nucleoside yields:
one nucleobase, one sugar, and three phosphates
after complete hydrolysis a nucleotide yields:
three bases, three sugars, and at least two phosphates
what does a nucleoside triphosphate consist of?
nitrogenous base bound to a 5 carbon sugar, with 3 phosphate groups bound to the sugar
how do you create a nucleoside mono-phosphate?
2 inorganic phosphate (Pi) are removed forming the nucleoside mono-phosphate that is then added to the growing DNA strand
the creation of a nucleoside mono-phosphate is what type of reaction?
exergonic reaction
what does it mean that the two DNA strands in a double stranded DNA are anti-parallel?
they are arranged opposite from one another, going in opposite directions (5’ to 3’) (3’ to 5’)
DNA polymerase can only add nucleotides to what end of the daughter DNA strand or the RNA primer?
3’ end of the daughter DNA strand
when the 3’ to 5’ strand is used as a template what occurs? what is it normally called and why?
referred to as the leading strand because it is continuous
when the 5’ to 3’ strand is used as a template what occurs? what is it normally called and why?
reffered to as the lagging strand because its disconinuous
in what direction can DNA polymerase not assemble a daughter strand? (5’ to 3’) or (3’ to 5’)
3’ to 5’ therefore the strand that has a template as 5’ to 3’ is called the lagging strand
what small fragments are produced when the template strand is 5’ to 3’?
okazaki fragments
what fills in the gaps (okazaki fragments)?
DNA ligase
how does DNA ligase work?
joins the sugar phosphate backbone together
what ratio of nucleotide errors are initially found?
1:10^5
after proof reading the errors what ratio of errors will remain in the final DNA molecule?
1:10^10
what is used to proofread the nucleotides?
DNA polymerase
how does DNA polymerase fix the error found?
removes the nucleotide and resumes synthesis of the daughter strand
what do mismatch repair enzymes do?
repair mismatched base pairs in DNA that the polymerase has missed
what do nucleases do?
cut out damaged DNA and replace the segment according to the undamaged template
what is used to fill in the gaps of the cut out DNA?
DNA polymerase and DNA ligase
what do skin cells have to repair damage to DNA due to UV light?
enzymes
what happens when replicating the ends of linear DNA?
the strand gets shorter and shorter due to the fact that there will not be a 3’ end available for nucleotide addition
do the chromosomes of prokaryotes have the same problem with getting shorter for every replication?
no because they have circular chromosomes
what do linear DNA sequences have at their ends to postpone erosion of genes located near the end of the DNA molecule?
telomere sequences
though we have a special telomere sequence at the ends of linear DNA what is inevitable of happening?
erosion of genes
they will become shorter regardless with every round of DNA replication
what does telomerase do in germ cells?
catalyzes the lengthening of telomeres in germ cells
what does it mean that telomerase catalyzes the lengthening?
restores the original length and prevents shortening
telomerase is not necessary and is therefore inactive in what cells?
somatic cells (body cells)
ex. skin cells
do bacteria contain lots of protein
no, only a small amount of protein, because they have single, circular stranded chromosomes
DNA in E.coli is how much longer than the E.coli cell?
500x longer than inself
because the DNA in E.coli (bacteria) is so long, how does it all fit in the cell?
DNA gets compressed
protein allows DNA to coil so that it occupies only the nucleoid region
do eukaryotes have lots of protein?
yes, and therefore have linear chromosomes
how many out of 46 chromosomes contain 1.5x10^8 base pairs?
1/46
how long is a chromosome when ironed out in a eukaryotic cell?
~4cm in length
how does such long DNA fit in the tiny nucleus?
elaborate packing system
chromatin coils in preparation for what?
mitosis
what are the two major categories of chromatin higher order structure?
heterochromatin
euchromatin
what is heterochromatin?
condensed chromatin structure and is inactive for transcription
what is euchromatin?
loose chromatin structure and active for transcription
