dna replication packet #43 chapter #16 tuesday, october 13, 20151

DNA Replication

Packet #43Chapter #16

Friday, April 21, 20231

Historical Facts About DNA


Historical DNA Discoveries 1928

Federick Griffith finds a substance in heat-killed bacteria that “transforms” living bacteria

1944 Oswald Avery, Cloin MacLeod and Maclyn McCarty

chemically identify Griffith’s transforming principle as DNA

1949 Erwin Chargaff reports relationships among DNA bases

that provide a clue to the structure of DNA 1953

Alfred Hersey and Martha Chase demonstrate that DNA , not protein, is involved in viral reproduction.

1953 Rosalind Franklin produces an x-ray diffraction image of

DNA


Historical DNA Discoveries II 1953

James Watson and Francis Crick propose a model of the structure of DNA.

1958 Matthew Meselson and Franklin Stahl demonstrate that

DNA replication is semi conservative replication 1962

James Watson, Francis Crick and Maurice Wilkins are awarded the Nobel Prize in Medicine for discoveries about the molecular structure of nucleic acids.

1969 Alfred Hershey is awarded the Nobel Prize in Medicine

for discovering the replication mechanism and genetic structure of viruses


Griffith Experiment


The Griffith experiment, conducted in 1928, was one of the first experiments suggesting that bacteria are capable of transferring genetic information through a process known as transformation.

Hershey Chase Experiment


Hershey and Chase conduced an experiment using viral DNA to show that the DNA was the genetic material being inserted into the bacteria and used to replicate more viruses.

Structure of DNA


Introduction I


DNA is an organic macromolecule known as a nucleic acid.

Nucleic Acids are composed of building blocks known as nucleotides.

Nucleotides have three parts: - Phosphate Sugar Nitrogenous bases

DNA Nucleotides Multiple DNA nucleotide subunits link together

to form a single DNA strand. DNA nucleotides are composed of: -

Phosphate Sugar

Deoxyribose Nitrogenous Bases

Purines (Two Rings) Adenine Guanine

Pyrimidines (One Ring) Thymine Cytosine


DNA Nucleotides II


Nucleotides are linked together by covalent phosphodiester bonds

Each phosphate attaches to the 5’ end (carbon #5) of one deoxyribose and to the 3’ end (carbon #3) of the neighboring deoxyribose Makes up the sugar-

phosphate backbone

DNA Strands


Each DNA strand, that is composed of multiple nucleotides, has a head and a tail. Head = 5’ end

Phosphate group Tail = 3’ end

Hydroxyl group

DNA Molecule


Each DNA molecule consists of two DNA strands (polynucleotide chains) that associate as a double helix

The two strands/chains run antiparallel

Base-Pairing Rules for DNAChargaff Rules


The two DNA strands are joined together at the nitrogenous bases.

Holding the bases together, and allowing the formation of the double helix, are hydrogen bonds.

Base-Pairing Rules for DNAChargaff Rules II


Adenine forms two hydrogen bonds with thymine

Guanine forms three hydrogen bonds with cytosine These pairings are

known as Chargaff’s rules A always pairs with T G always pairs with C

Complementary base pairing

Chargaff Rules III


Models of DNA Replication


Models of DNA Replication


There were three models proposed about how DNA replicates.

However, the one that stood the test was semi-conservative replication.

DNA Replication Introduction


In semi-conservative replication, each “old” strand of DNA is used to create a new complementary strand.

Introduction to DNA Replication

The Players


Introduction to the Strands


Template Strands {The Parental Strands} Are the strands

being copied The original DNA

strands During DNA

replication, both strands are copied This means that there

are TWO template strands

Introduction to the Strands II


Complementary Strands {The Daughter Strands} The NEW DNA strands

produced from the Template Strands

During DNA replication, there are TWO complementary strands Always remember that

the process started with TWO template strands

Origin of Replication & Bi-directionality.


DNA replication is bidirectional and starts at the origin of replication The process proceeds

in both directions from that point.

A eukaryotic chromosome may have multiple origins of replication Allows the process to

occur faster and more efficient

Introduction to the Making of the Complementary Strand.


DNA replication/synthesis, of the complementary strands, proceed in a 5’ to 3’ direction. Nucleotides can ONLY

be added to the 3’ end.

Introduction to the Making of the Complementary Strand.


Since DNA nucleotides can only be added to the 3’ end, it causes one of the complementary strands to be produced continuously and the other discontinuous The continuous strand is

called the leading strand The discontinuous strand

is called the lagging strand Is first synthesized as

short Okazaki fragments before becoming one strand

Enzymes of DNA Replication & The Steps of DNA Replication


Enzymes of DNA Replication


Helicase Unzips DNA double-helix

Topoisomerases Prevents tangling and

knotting of DNA as the while the strands are unzipped.

RNA primase Initiates the formation of

“daughter” strands Forms a segment known

as the RNA primer The RNA primer contains

the nitrogenous base Uracil

Enzymes of DNA Replication II


DNA Polymerase III Enzyme that catalyzes the

polymerization (making) of nucleotides

Adds Deoxyribonucleotides (nucleotides only found in DNA, as opposed to RNA) to the 3’ end of a growing nucleotide chain

Acts at the replication fork DNA Polymerase I

A type of DNA polymerase will change the RNA primers into DNA Changing the base Uracil

into Thymine

Enzymes of DNA Replication III


DNA Ligase Enzyme responsible

for joining Okazaki fragments forming the Lagging Strand

Gyrase Returns the DNA

strands into a Double Helix

Zips the DNA back together

DNA Replication—The Big Picture


DNA Replication—Lagging Strand


Post DNA Replication


DNA Excision RepairDNA Polymerase II


On some occasions, errors in nucleotides may occur while making the new DNA strand. Errors such as

mismatches & dimers may occur.

To correct these errors, the enzymes nuclease, DNA polymerase III and DNA ligase are used during the process known as excision repair.

Telomeres, Telomerase & DNA Shortening


At the end of eukaryotic chromosomes are known as telomeres Short, repetitive DNA

sequences that do not contain genes. Typically 100 to 1000

nucleotides TTAGGG (Humans)

Telomeres help protect the organism's genes from being eroded through successive rounds of DNA replication.

Telomeres, Telomerase & DNA Shortening


Telomeres shorten each cell cycle (DNA replication sequence) but can be extended using the enzyme telomerase Absence of telomerase in

certain cells may be the cause of “cell aging” Cells having a limited

number of cell divisions Most cancer cells have

telomerase to maintain the telomeres and possibly resist apoptosis.

dna replication packet #43 chapter #16 tuesday, october 13, 20151

Documents

dna bases

viral dna

single dna

dna replicationpacket

dna replicates

models of dna replication

xray diffraction image

replication introduction