DNA Structure & Function Watson, Crick, and Franklin’s crystallography image

Some important vocabulary 1.DNA 2.Gene 3.Chromatin 4.Chromatid 5.Chromosome 6.Protein 7.Replication 8.Transcription 9.Translation 10.Dogma 11.Phosphodiester-bond 12.Hydrogen bonds

DNA Deoxyribonucleic acid

What is DNA? DNA is the code for making of proteins used for structure and function (enzymes).

The Central Dogma “the fully accepted thoughts or ideas” DNA → mRNA → Protein → Trait Transcription Translation

What is the “central dogma?” Dogmatic ideas are those that govern irrefutably. (No one argues with it) In biology, the central dogma is that DNA carries the code necessary to build life and the components needed for life

How did scientists know that DNA carries the information for life? Many thought that proteins instead of DNA were inherited from parent to offspring. Scientists (Griffith, Hershey and Chase, Chargaff, etc) showed that DNA actually carries the blueprint.

Hershey and Chase’s experiment Bacteriophage with phosphorus-32 in DNA Phage infects bacterium Radioactivity inside bacterium Bacteriophage with sulfur-35 in protein coat Phage infects bacterium No radioactivity inside bacterium

Griffith’s experiment Disease-causing bacteria (smooth colonies) Harmless bacteria (rough colonies) Heat-killed, disease- causing bacteria (smooth colonies) Control (no growth) Heat-killed, disease-causing bacteria (smooth colonies) Harmless bacteria (rough colonies) Dies of pneumoniaLives Live, disease-causing bacteria (smooth colonies) Dies of pneumonia

Griffith’s Experiment S strain – deadly R strain – harmless S strain (heated) – harmless S strain (heated) + R strain – deadly Transformation – when one bacteria takes up genetic information of another bacteria, changing it’s phenotype

Deoxyribonucleic Acid Nucleotides –Building block of DNA

After determining the connection between DNA and genetics, figuring out the structure of DNA became important. Each strand of DNA is made of repeating nucleotide units. A nucleotide is either a purine or a pyrimidine. Purines Pyrimidines AdenineGuanine CytosineThymine Phosphate group Deoxyribose

Adenine Nucleotide Guanine Nucleotide Cytosine Nucleotide Thymine Nucleotide The 4 DNA Nucleotides Phosphate Deoxyribose Phosphate G A T C Deoxyribose Phosphate

Nitrogenous Bases Purines: –Adenine –Guanine Pyrimidines: –Thymine –Cytosine Antiparallel structure: 5’(phosphate) to 3’(sugar)

DNA: the genetic basis of life Do you notice any commonalities in the percentages of adenine, thymine, guanine, and cytosine? Between species? Source of DNAATGC Streptococcus Yeast Herring Human Streptococcus Yeast Herring Human

Base Pairing Chargoff’s Base-pairing rule: –Adenine always bonds with Thymine –Guanine always bonds with Cytosine

Hydrogen Bonds Three between G & C Two between A & T

Nitrogen(ous) bases pair up 1. Adenine pairs with Thymine A T 2. Guanine pairs with Cytosine G C

Rosalind Elsie Franklin (25 July 1920 – 16 April 1958)

Franklin is best known for her work on the X-ray diffraction images of DNA which led to discovery of DNA double helix. Her data, according to Francis Crick, was "the data we actually used to formulate Crick and Watson's 1953 hypothesis regarding the structure of DNA.

Rosalind Elsie Franklin (25 July 1920 – 16 April 1958) Franklin's X-ray image, confirming the helical structure of DNA, was shown to Watson without her approval or knowledge. Though this image and her accurate interpretation of the data provided valuable insight into the DNA structure, Franklin's scientific contributions to the discovery of the double helix are often overlooked.

Watson and Crick won the Nobel Prize in 1962 for figuring out the DNA is actually 2 strands twisted together, called a double helix. Hydrogen bonds Nucleotide Sugar-phosphate backbone Key Adenine (A) Thymine (T) Cytosine (C) Guanine (G)

Phosphodiester bonds create the backbone (side rails) of DNA

Phosphodiester bond Phosphodiester bonds make up the sugar/phosphate backbone of the strands of DNA. (Pre AP) In DNA and RNA, the phosphodiester bond is the linkage between the 3' carbon atom and the 5' carbon of the sugar ribose

Double helix structure

DNA Structure Remember: Nucleic acid is the polymer that is made up of monomers called NUCLEOTIDES

Bacterial DNA Chromosome E. coli bacterium Bases on the chromosome Prokaryotic DNA is a single loop of genetic material.

Eukaryotic DNA Chromosome Supercoils Coils Nucleosome Histones DNA double helix Eukaryotic DNA is in the form of linear chromosomes.

Why do cells divide/replicate? Cells replicate for –Growth –Replacement –Repair –GRR!!!!!

Before DNA replication begins… Chromosomes must be “unwound” back to chromatin through the removing of histone proteins.

What is Replication DNA replication is the process of creating new IDENTICAL strands of DNA. Replication happens before a cell begins cell division.

Replication

When does DNA replication take place? Replication happens in the S stage of interphase in the cell cycle “S” stands for synthesis (to make) of DNA During the S stage, DNA is not only copied it is also repaired if the cell finds something wrong

What does replication do? DNA replication creates identical copies of DNA by using one strand as a template. The original strand is used as a template along with “Chargoff’s rules” to base pair up the complementary strand

Replication Example Original DNA: T A C G C C A T T A G C Using Chargoff’s rules A pairs with T AND G pairs with C, so… Original DNA: T A C G C C A T T A G C Complementary DNA: A T G C G G T A A T C G

Semiconservative Because each new strand of DNA has ½ of the original DNA, its called SEMICONSERVATIVE

DNA synthesis overview A B C D

Enzymes for DNA replication Helicase Single stranded binding protein Topoisomerase DNA polymerase Ligase

DNA Replication 1. Replication fork made when Helicase separates parent strands Helicase “unzips” the two sides 2. DNA polymerase links new nucleotides to the growing strand (only on the 3’ end) 3. Leading strand made as single polymer 4. Lagging strand is produced in a series of short fragments (Okazaki fragments) 5. Ligase joins Okazaki fragments

Helicase Breaks hydrogen bonds between nitrogen bases of nucleotides Opens double helix starting at origin of replication Helicase

Topoisomerase & SSBP SSBP (single stranded binding proteins): stabilize open helix because DNA is stable when double-stranded Topoisomerase: helps to relieve the tension created when helicase creates “replication bubble”

Topoisomerase and SSBP SSBP Topoisomerase SSBP Topoisomerase

DNA polymerase Builds DNA polymer according to Chargaff’s base pairing rules A – T C – G DNA polymerase also “edits” to check for mistakes in the DNA.

DNA polymerase Polymerase can ONLY add onto the 3’ end with they –OH group. DNA can not be created by adding to the 5’ end that has the –(phosphate group)

DNA polymerase 5’ – A A A T T C G T 3’ – T T T A A G C A A T C G A T T A C A - 3’ T A A T G T - 5’ ATAT TATA CGCG GCGC Leading strand Lagging strand

DNA replication in 5’ to 3’ direction Growth Replication fork DNA polymerase New strand Original strand DNA polymerase Replication fork Original strand New strand

Leading vs. Lagging strands Leading strand: made continuously Lagging strand: made in fragments (called Okazaki fragments)

Ligase Connects the pieces of Okazaki fragments together

Why do we need DNA? DNA is the code for the making of proteins used for structure & function(enzymes).

What is a Gene A gene is a sequence of nitrogenous bases (segment of DNA) that code for a trait. The gene is stored in the sequence of bases GENE