Exam1 - Ch. 8-11, 1-3 Flashcards
central dogma of molecular biology
describes the flow of genetic information from DNA to RNA to proteins
- DNA replication
- transcription
- translation
what is the substance of inheritance?
traits (phenotypes) are passed on from generation to generation
1868
Johann Friedrich Miescher
isolated the nucleus
determined the large amount of a substance that is high in phosphorous and is slightly acidic
this material contained both DNA and proteins
1887
Albrecht Kossel
DNA is composed of 4 nitrogenous bases: adenine, cytosine, guanine, and thymine (ACGT)
1919
Phoebus Aaron Theodore Levene
nucleic acids are composed of “nucleotides”
each nucleotide has a base, a sugar (ribose or deoxyribose) and a phosphate group
1955
Erwin Chargaff finds that DNA contains equimolar amounts of A&T and C&G
if DNA molecules 40% G, what % is A?
G=C A=T G+C = 80% A+T = 20% / 2 = 10% A=10%
1929
Fred Griffith
discovered “killing property” (phenotype) can be transferred into harmless strain - “bacterial transformation”
transformation
harmless R cells are transformed into deadly S cells when mixed with heat-inactivated S debris
no living S-cells required for R to S transformation
1944
Oswald Avery et al.
DNA is the genetic material sufficient to do transformation
candidate substances: protein, RNA, DNA
protein-destroying enzyme (protease)
RNA-destroying enzyme (RNase)
-both have an effects on S to R transformation
-proteins and RNA are not the genetic material
DNA-destroying enzyme (DNase)
»destroys transformation ability of S-debris R to S (harmless to killer)
nucleotides (deoxyribonucleotides)
2’ - deoxyribose (a five-carbon sugar)
phosphoric acid
one of four nitrogen-containing bases denoted A, T, G, and C
Chargaff Parity Rule
%A = %T and %G = %C
H Bonding
A=T 2 hydrogen bonds
G=C 3 hydrogen bonds
sugar-phosphate backbone of polynucleotide strands
deoxyribose sugars alternating with phosphate groups
phosphate links
5’ and 3’ carbon of adjacent sugars
covalent chemical bonds
phosphodiester bond
antiparallel
2 polynucleotide strands run in opposite directions
Watson and Crick
structure of DNA (double helix)
paired bases on single plane (planar)
ribose rings not planar
major/minor grooves
major groove
1 helical turn
10 basepairs (bp) =
34 Angstrom =
3.4 nanometer
3D DNA structure (Watson and Crick)
2 polynucleotide chains twisted around one another as right-handed helix
“right-handed double helix” : clockwise turns away from observer (backbone)
strands connected via hydrogen bonds between stacked bp
paired bases planar, parallel to one another, perpendicular to the long axis of the double helix
Rosalind Franklin
X-ray
diffraction pattern
used to determine 3D structure of DNA
DNA form (2 of 3) B form
most common under physiological conditions
typical right handed helix
DNA form (1 of 3) A form
short and fat
exists when less water is present
uncommon in most physiological conditions
DNA form (3 of 3)
left handed DNA
can occur in cells undergoing active transcription and in regions of DNA that have alternating C-G nucleotides
Watson-Crick model of DNA replication
Each DNA strand template for synthesis of new strand
hydrogen bonds between DNA bases break > strand separation
template (parental) strand determines sequence of bases in new strand (daughter) = complementary strand preserves genetic information
how is DNA packaged into chromosomes
via a special coiling around itself that only depends on DNA (“negative supercoiling”)
plus association with various proteins that help packaging the DNA
human genome
6 billion base pairs (2meters in length)
typical nucleus about 5 microns in diameter
advantages of supercoiling
separation of strands during replication/transcription is faster and requires less energy
can be packed into smaller space
topoisomerases
enzyme breaks DNA strands passes one end through it then repairs
positive supercoil
overrotate
negative supercoil
underrotate
1st step in central dogma
replication
semiconservative replication
each of the original nucleotide strands remains intact (conserved)
the original DNA molecule is half (semi) conserved during replication
1958
Meselson and Stahl
parental strands serve as templates for new strands
characteristics of replication
semiconservative replication can take place in several ways
-circular (bacteria)
-linear (most eukaryote)
-replicons (units of replication)
-replication origin (OR; start site)
-replication bubble (unwinding of the double helix)
-replication fork (point where the nucleotide strands separate from the DNA helix)
replication bubble moves away from replication fork
requirements of replication
template of ssDNA raw materials (substrates) to be assembled into a new nucleotide strand enzymes/proteins that "read" the template and assemble the substrates into DNA molecule
dNTPs
deoxyribose sugar + a base (nucleoside)n + 3 phosphates
how are new nucleotides added?
dNTPs
building blocks (substrates) of new DNA molecules
added to the 3’-hydroxyl (OH) group of the growing nucleotide strand
how is circular DNA replicated?
E. coli
DNA synthesis is often bidirectional, but can be unidirectional
replication starts from a single origin of replication, producing a theta structure
as parental strands separate and new strands are being synthesized, a replication fork forms
