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

Some important vocabulary DNA Gene Chromatin Chromatid Chromosome Protein Replication Transcription Translation Dogma Phosphodiester- bond Hydrogen bonds

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

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

What is the “central dogma?” Dogmatic ideas are those that govern irrefutably. 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) 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 –1 phosphate + 1 deoxyribose sugar + 1 nitrogen base

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

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

Bonds Hydrogen bonds: –Triple = G + C –Double = 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 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

Think Pair Share Or Stand Up, Hands Up, Pair Up

Double helix structure

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

Bacterial DNA Chromosome E. coli bacterium Bases on the chromosome

Eukaryotic DNA Chromosome Supercoils Coils Nucleosome Histones DNA double helix

Before 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. Both new daughter strands are identical to each other AND to the original DNA strand.

DNA Replication

When does replication take place? Replication happens in the S phase of interphase During the S phase, 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 template is used 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

Think Pair Share Or Stand Up, Hands Up, Pair Up

(Pre AP) Enzymes for DNA replication Helicase Single stranded binding protein Topoisomerase DNA polymerase Ligase

DNA Replication (Pre AP) in red 1. Replication fork made when Helicase separates parent strands 2. DNA polymerase links new nucleotides to the growing strand (only in the 5’ to 3’ direction) 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 (Pre AP) Breaks hydrogen bonds between nitrogen bases of nucleotides Opens double helix starting at origin of replication Helicase

Topoisomerase & SSBP (Pre AP) 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 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 (Pre AP) Leading strand: made continuously Lagging strand: made in fragments (called Okazaki fragments)

Ligase (Pre AP) Reforms bonds between parts of the nucleotides and between 2 nucleotides.

What is DNA? DNA is the code for the making of proteins used for structure & function.

What is a Gene A gene is a sequence of nitrogenous bases in a piece of DNA GENE

What actually stores genes? The sequence of the nitrogenous bases is how genetic information is stored T A C A G G T A G G G G A C A C C …