DNA Flashcards
ground zero for DNA
Parents pass genetic traits on to their offspring (inheritance)
Chromosomes in a cell’s nucleus carry the traits
Chromosomes are made of DNA and Proteins Histones we can conclude Genetic info is carried by either DNA or protein
Griffith
discovered bacteria give genetic traits to other bacteria. The trait they passed on was ability to secrete a capsule
what did griffith not know
Didn’t know if DNA or protein was being traded
smooth colonies vs rough colonies
smooth colonies secrete a capsule, rough ones dont
Avery
1st to show DNA is the genetic material.
Showed that only DNA could transfer a trait from one bacteria to another….
give rough bacteria the ability to make a capsule
What was averys experiment
took cells, seperated them into RNA, protein, DNA, lipids and carbs. The only ones secreted was through DNA
why was avery criticized and not trusted
felt breaking cell down into so many parts was not reliable and did not trust his experiments
Background for hershey and chase
Viruses are only made of DNA and Protein
Viruses transfer their genes to other cells
DNA has phosphate, but Protein does not
Protein has sulfur but DNA does not
Bacteriophage Viruses inject genetic material into bacteria
Hershey and Chase
create viruses with radioactive DNA
Let viruses put their genetic material into a bacteria
If the bacteria is then radioactive, the genetic material is DNA
If the bacteria is NOT radioactive, the genetic material is Protein
who found conclusive evidence that DNA is genetic material
hershey and chase
Chargaff
Showed that there was always the same amount of A nucleotides as T nucleotides and
There were always the same amount of G as C
chargaffs rule
A=T C=G
what clue did chargaff give to watson and crick
A is linked to T and G is linked to C
Background for Franklin
DNA molecules are too small to see with a microscope
Visible light’s wavelenth is too long & goes around it
X – rays have shorter wavelenth and bend around DNA
Bending light is called diffraction
The pattern of bending can be used to identify the shape of the object that bends it
Franklins experiment
Took X-ray diffraction photos of DNA
Measured the diffraction patterns
what did Franklin conclude
concluded
DNA was a helix and calculated the diameter of the DNA molecule
What is watson and cricks based on
Based on the fact that DNA contains the 5-carbon sugar Deoxyribose.
Based on Chargaff’s Rule
Based on Franklin’s photo showing a helical shape
what did watson and crick do
Constructed the first working Model of DNA’s structure
Overall summary of the scientists findings
Griffith – bacteria give genetic traits to other bacteria.
Avery – 1st to show that DNA is the genetic material.
Hershey & Chase – Showed conclusively that DNA is the genetic material
Chargaff – A = T and G = C
Franklin – x-ray diffraction
Watson & Crick – model of DNA
DNA structure
DNA is made of subunits called Nucleotides
Nucleotides are made of 3 parts :one 5 carbon sugar, phosphate, and a nitrogen containing base
Nucleotides bonds
bonded together in two chains, covalent bonds hold one nucleotide to the next
Backbone of the double helix
strong covalent bonds between phosphates and sugars
how are the two chains of nucelotides bonded together
with weak hydrogen bonds between bases
how does DNA get its double helix
2 chains of nucelotides are twisted to form a double helix with weak hydrogen bonds
how do cells store DNA
The cell stores DNA wrapped around proteins called histones to form a bundle called a nucleosome
Further wrapping of DNA forms what
X-shape showed in mitosis
semi conservative replication
One double helix is replicated so there are 2 double helixes.
1 molecule of DNA becomes 2 molecules of DNA
Each molecule retains one of the original chains of nucleotides
replication origins
In eukaryotes where replication takes place at multiple replication origins at the same time
replication fork
The area where the 2 strands of parental DNA are being separated is a
parent strands
The original DNA strands (chains of nucleotides)
daughter strands
The strands formed of new nucleotides
what is the relationship between daughter and parent strands
Daughter strands are complimentary to parent strands
The two strands are antiparallel (5’ -> 3’ and 3’ -> 5’)
DNA replication location
the nucleus
helicase
unwinds double helix & breaks H-bonds
SSBP proteins
keep parental strands apart, single stand binding protein keep the strands apart because h bonds are like magnets
Topoisomerase
cuts DNA to let it untwist then puts it back together, isomerase enzymes that act on the topolody of DNA
primase
matches RNA primer to parent strand
DNA Polymerase
adds DNA nucleotides to 3’ end of RNA primer to grow the daughter strand from 5’ -> 3’
ligase
fuses Okazaki fragments together
DNA proof reading & repair
DNA Polymerases proofread as they build
After replication….
Nuclease enzymes cut out errors and DNA Polymerase fills in correct code where the error was cut out
what happens everytime a chromosome is replicated it
gets shorter
telomeres
long stretches of non-coding DNA at the end of each chromosome
how do cells keep from losing genes
eukaryotes have telomeres
telomere length is restored where and how
in germ cells by telomerase
where is the Gene for telomerase not active
in somatic cells
DNA
Deoxyribonucleic acid
Both use phosphate
Bases are GCAT
Double stranded molecule
RNA
Ribonucleic acid
Both use phosphate
Bases are GCAU
Single stranded molecule
Pyrimidines
only one carbon ring, include Cytosine, Thymine, Uracil
purines
two carbon rings
include Guanine, and Adenosine
nitrogeneous bases in nucleotides
pyrimidines and purines
prokaryotes
circular double helix DNA
eukaryotes
multiple liner double helix DNA molecules (combined with histones form chromosomes)
nucleotide evolution
Nucleotide structure and base pairing conserved in all organisms and viruses
Evidence of evolution from a common ancestor
Semiconservative replication in all organisms & viruses
what does topoisomerases do to overcome problems with double helix
bind to either single-stranded or double-stranded DNA and cut the phosphate backbone of the DNA
how is DNA unwound
when topoisomerase breaks the phosphate backbone
how are DNA chemical isomers
the overall chemical composition and connectivity of the DNA does not change, the tangled and untangled DNAs are chemical isomers, differing only in their global topology
thymine dimer caused by
u-v light on skin cells
thymine dimer
Thymine bases on same strand form covalent bond to each other instead of to their Adenine partners on the complimentary strand.
what does nuclease do to thymine dimer
cuts out dimer
what does polymerase do with thymine dimer
synthesizes new strand by base pairing
what does ligase do with thymine dimer
fuses new DNA in place
mutations
If DNA is replicated with an error still in place…The error is permanent and = a mutation, most bad
can mutations be passed on
mutations in germ cells or gametes can be passed on
what is the source of variation that allows natural selection
mutations
chromosomes
naturally occurring segment of DNA and associated proteins
linear in eukaryotes
circular in prokarytotes
chromosome forms
chromatin
chromatid
chromatin
DNA wrapped around histones
no supercoiling
Most DNA available for transcription
not visible under microscope
chromatid
nucleosomes supercoiled into compact ‘arms’
DNA packaged for transport not use
condensed chromosomes visible
constriction in center of condensed chromatids
centromere
centromere
a region of DNA that binds to cohesin proteins that function to hold sister chromatids together
sister chromatids
Identical: each chromatid = one of the double helix molecules made by replication
Formed by semi-conservative replication
Differential Gene expression
Means different cells express different genes
Even though all cells in a body have the exact same DNA
example of differential gene expression
The gene that codes for making telomerase is in every cell, but is only activated/used in germ cells that make eggs and sperm
gene expression can be controlled by
bonding functional groups to histones
bonding functionsl groups to DNA
bonding functional groups to histones
Histone acetylation
encourages use of gene
Histone methylation
inactivates gene
Bonding functional groups to the DNA
DNA methylation inactivates genes
When methylated genes are replicated the daughter strand will be methylated too…passing on the inactive gene state.
What does nuclease do?
Cut out error parts in dna proof reading and repair
Okazachi fragment
Pieces that make up lagging strand
