DNA Structure & Analysis - Chapter 9 Biology Study Guide

DNA is the

genetic material

genetic material has three properties

-storage and expression of information

-replication

-variation through mutation

work with bacteria and bacteriophages shows that shows that

DNA is the genetic material

griffith's experiments (1927) on Streptococcus pneumoniae

-something from IIIS "transforms" IIR

-chemical substance is involved

-physiological vs. genetic

-living R + heat killed -> S virulent

Streptococcus pneumoniae

-rough strain: avirulent

-smooth strain: virulent

Avery, MacLeod, and McCarty (1944)

-"nucleic acid of the deoxyribose type" is the transforming agent

-once transformation occurs, it is heritable

1. protease 2. RNAse 3. DNAse

transfection experiment provided the conclusive evidence that

DNA is the genetic material

transfection

the process of infection by viral DNA only into bacterial cells

hershey & chase show that DNA is the

genetic material in bacteriophages (1952)

bacteriophage has

DNA and protein

phage is made up of

50% protein and 50% DNA

hershey and chase experiment

-DNA labeled 32P

-protein coat labeled 35S

-viruses were isolated

-infect E. coli w labeled viruses

end of hershey and chase experiment

strongest direct evidence for DNA as the genetic material comes from

recombinant DNA technology

segments of eukaryotic DNA corresponding to specific genes are

isolated and spliced into the bacterial DNA

presence of the eukaryotic gene product in bacteria containing the eukaryotic gene provides

direct evidence that this DNA is present and functional in the bacterial cell

DNA is the genetic material in

all organisms

RNA viruses do not have

DNA

-e.g. Tobacco Mosaic Virus

-RNA genome

-protein coat

RNA as the

genetic material in some viruses

experiments with tobacco mosaic virus (1956) demonstrated that

RNA serves as the genetic material for these viruses

replication of the viral RNA is dependent on

RNA replicase

other RNA viruses

retroviruses

biochemical nature of the genetic material influences

the biology of a virus

retroviruses replicate in an

unusual way

RNA serves as a template for

synthesis of a complementary DNA by the RNA-dependent DNA polymerase called reverse transcriptase

this DNA (reverse transcriptase) can be incorporated into

the host-cell genome

when transcribed, copies of the original retroviral RNA chromosomes are

also produced

-HIV

structure of DNA holds the key to understanding its

function

biochemistry is the basis for

life

DNA is a

polymeric macromolecule

DNA is

a nucleic acid

nucleotides are the building blocks of

DNA

nucleotides consist of

-nitrogenous base

-a phosphate group

-a pentose sugar

nitrogenous bases end in

ine

-cytosine

-thymine

-uracil

-guanine

-adenine

components of DNA have descriptive terms that

indicate what each unit includes

nucleoside contains the

nitrogenous base and the pentose sugar

nucleotide is a

nucleoside with a phosphate group added

(deoxy)ribonucleosides can be

mono- di or tri-phosphorylated

biological DNA is a

directional polymer of nucleotides

nucleotides are linked by a phosphodiester bond between

the phosphate group at the C-5' position and the OH group on the C-3' position

oligonucleotides

short chains consisting of up to 20 nucleotides or so

polynucleotides

longer nucleotide chains

oligo/polynucleotides

-store vast amounts of genetic information

-give rise to extraordinary variation

DNA goes from

5' to 3'

forming these 3'-5' phosphodiester bonds is the basis of

DNA synthesis

early observations gave important clues about the

structure of DNA in cells

with base composition studies, Chargaff and his colleagues quantitatively demonstrated that

-amount of adenine is equal to amount of thymine and amount of guanine is equal to amount of cytosine (A = T & G = C)

-the sum of purines (A + G) = sum of pyrimidines (C + T)

-percentage of (G + C) is not necessarily equal to the percentage of (A + T)

Erwin Chragaff's data

A = T & G = C

X-ray diffraction studies by Rosalind Franklin (1950-1953) of DNA showed a

3.4 angstrom periodicity, characteristic of a helical structure

Watson-Crick Model incorporated

base composition and x-ray diffraction to describe structure of DNA

Watson and Crick (1953) proposed that DNA is a

right-handed double helix in which the two strands are antiparallel and bases are stacked on one another

two strands are connected by

A-T and G-C base pairing

there are ____ base pairs per helix turn

10

Watson and crick model is the currently accepted model for

the structure of DNA in cells

base composition data relates to

complementary base pairing in the DNA molecule

A-T and G-C base pairing provides

complementarity of the two strands and chemical stability to the helix

two strands are

antiparallel

one chain runs

5'-to-3', whereas the other runs 3'-to-5'

the structure is critical to how the dna molecule is

synthesized

dna is a very stable molecule

-H bonds in middle

-SP backbone

-double stranded

DNA

double helix held together bycomplementary base pairing

A-T has ___ hydrogen bonds

2

G-C has ___ hydrogen bonds

3

physical/chemical properties of DNA depend on its

G+C %

density of DNA depends on its

G+C%

melting temperature increases with

G+C %

Tm

temp at which DNA is 50% melted

denaturation of dna

separation of complementary strands

-heating and high PH

renaturation of dna

base pairs to reform

-low temp

-low pH

renaturation rate of DNA from different sources is proportional to

genome size

-so-called cot curves

analytical methods are possible because of

biochemical nature of analyzed molecules

analytical methods are based on the unique nature of the

hydrogen bond that is so integral to the structure of nucleic acids

-heated DNA heat denatures (1 molecule becomes 2)

during "melting", the viscosity of nucleic acids

decreases and absorption of UV light increases (hyperchromic shift)

absorbs most strongly at

254-260 nm due to interaction between UV light and ring systems of the bases

hyperchromic shift is used to measure

melting temperature

-informative about base composition of DNA strand (need >̊ to break G=C)

denaturation/renaturation of nucleic acids is the basis for

molecular hybridization

molecular hybridization is possible between

DNA strands of different organisms

RNA molecules will hybridize with

segments of DNA from which it was transcribed

probes are used to identify

complementary sequences

hybridization depends on

complementary base pairing: probe to target

detecting DNA sequences by

molecular hybridization

hybridization can be done with

DNA in solution, on filters, or on chromosomes

B-DNA is the

common form of DNA

-3.4 nm per turn

-10bp per turn

-right handed

A-DNA

-2.6 nm per turn

-11 bp per turn

-right handed

Z-DNA

-3.7 nm per turn

-12 bp per turn

-left handed

-gcgcgcggc or atatatat)

RNA is very similar to DNA, with a couple important differences

different sugars and bases

RNA

single stranded but can form double stranded regions by base pairing with itself

-complex structures possible

secondary structure of tRNA

3d structure of tRNA

RNA has important

cellular functions

three classes of cellular RNAs that function during

expression of genetic info

-messenger RNA (mRNA)

-ribosomal RNA (rRNA)

-transfer RNA (tRNA)

messenger RNA (mRNA)

carries genetic information from DNA of the gene to the ribosome

-vary in size reflecting size of protein/gene

ribosomal RNA (rRNA)

-largest in size and constitute 80% of all RNA in a cell

-act as work benches during translation

transfer RNA (tRNA)

carries amino acids to ribosomes

in cells, RNA is almost always derived from DNA

RNA all originate as complementary copies of

one of the two DNA strands during transcription

in RNA Uracil replaces

thymine and is complementary to adenine during transcription

ther RNAs exist that perform various roles

-telomerase RNA (tRNA)

-small nuclear RNA (snRNA)

-Antisense RNA

-microRNA (miRNA)

-short interfering RNA (siRNA)

telomerase RNA (tRNA)

DNA replication

mall nuclear RNA (snRNA)

RNA processing