Transcription and Translation DNA Replication Transcription and Translation

Genes are Made of DNA Scientist discovered that DNA was a chemical inside the nucleus Oswald Avery 1944 Frederick Griffith 1928

Genes are Made of DNA Further experiments by: Alfred Hershey Martha Chase Worked with viruses to support Avery’s work

Genes are Made of DNA Virus – a package of nucleic acid wrapped in protein Not made of cells They can only reproduce by infecting a living cell Bacteriophage – a virus that infects bacteria

The Double Helix Double Helix – Model created by Watson and At more or less the same time scientist: James Watson Francis Crick Using Franklin’s X-ray crystalography to provide clues to their discovery Double Helix – Model created by Watson and Crick; in which two strands of nucleotides wound about each other Sugar phosphate backbones on the outside; Nitrogenous base on the inside.

Remember the monomer of DNA is a nucleotide https://www.youtube.com/watch?v=VegLVn_1oCE https://www.youtube.com/watch?v=IN8pKyQz2RQ

What is DNA and RNA?? DNA and RNA are a class of macromolecules called Nucleic Acids DNA (Deoxyribonucleic Acid) where genetic information is stored Composed of Deoxyribose sugar Phosphate group Nucleotide base Double stranded RNA (Ribonucleic Acid)- involved in protein synthesis Composed of the sugar ribose, a phosphate group, and nitrogenous base Has the nitrogen base uracil in place of thiamine

DNA - Nucleotides Each DNA and RNA monomer has three parts:

DNA - Nucleotides Nitrogenous Base – 4 nucleotides found in DNA differ only in their nitrogenous bases Pyrimidines: single ring structure Thymine (T) Cytosine (C) Purines: double ring structure Adenine (A) Guanine (G)

DNA structure and bonding DNA is composed of the sugar-phosphate “backbone” The nitrogenous bases “rungs” The sugar-phosphate molecules are joined by covalent bonds The nitrogen bases are joined by hydrogen bonds

Complementary Base Pairs Pyrimidines always pair with purines Base Pairing Rules A with T C with G AT CG (Coral Gables)

Chargaff’s rule If…. Adenine (A) only pairs with Thiamine (T) Guanine (G) only pairs with Cytosine (C) Then for every DNA molecule, the amount of A=T The amount of C=G C% + G% = 100%- (A% + T%)

Practice Problem A molecule of DNA is composed of 20% Adenine. What % is Thiamine? What % is Guanine? What percent is Cytosine?

A= 20% A=T; T=20% A+T= 40% (C% + G%) = 100% - 40%= 60% C = G, then

You Practice Given the following problems, figure out the % of the rest of the nucleotides 10 % guanine 15% thiamine 30% cytosine

You Do: Draw a DNA Molecule Draw a molecule of DNA Make sure to color code Phosphate Group Deoxyribose sugar Nitrogenous Bases Adenine Guanine Thymine Cytosine Show which bonds are hydrogen bonds and which are covalent bonds

DNA Replication When a cell divides; a complete set of genetic instructions are copied for each cell Genetic material uses the template principle to make more DNA Watson and Crick’s model for DNA allowed for the hypothesis of specific base pairing A – T C - G If you know one strand of DNA you can determine the sequence on the other

What is the essential vocabulary? Replication – the process of DNA duplication. Replication fork – Site where DNA strands separate and replication occurs. Enzyme – a protein that facilitates a specific chemical reaction in the body. Leading strand – DNA strand that forms as a continuous strand during DNA replication. Lagging strand – DNA strand that forms as a series of short segments, called Okazaki fragments, which are then connected together.

What is DNA replication? During DNA replication, the DNA molecule produces two new complementary strands. Each strand of DNA serves as a template for the new strand. Described as semiconservative because each DNA molecule has one new strand and one original strand. New nucleotides are always added in the 3’ to 5’ direction

How does DNA replication work? A very complex process requiring the assistance of several enzymes and regulatory molecules. DNA helicases unwind parent strand. Primase initiates replication by adding a short RNA fragment called a primer to the old strands DNA polymerases join individual nucleotides to produce a new strand of DNA using the old strand as a template. They also carry out DNA proofreading and repair. Ligase binds the DNA fragments together by addition of phosphates in the gaps that remain in the phosphate-ribose sugar backbone. These enzymes are the crucial parts of replication assembly line. The precision with which every single segment of the complementary strand is aligned is mind-boggling. No man-made assembly line can match the efficiency, detailing and brilliance of the DNA replication mechanism that makes biological inheritance possible. Helicase DNA replication begins at places called origins, within the DNA molecule and the creation of replication forks. The process of strand separation is made possible because of the enzyme Helicase which separates the two strands using the energy that is derived from ATP hydrolysis. DNA Primase One of the most crucial enzymes is DNA Primase. After the DNA strands are separated, to begin the creation of new DNA molecules, through addition of complementary bases to the templates, a short RNA segment, called a 'primer' is required. These primers are synthesized by DNA primase enzymes, thus initiating the DNA replication process. That is why DNA Primase is one of the most important DNA replication enzyme. DNA Polymerase The most important enzymes, that carry out the main task of aligning the complementary bases with template strands of 'unzipped' DNA, are the DNA polymerases. They are a large family of enzymes that carry out the task of adding complementary base nucleotides by reading the template strands. Besides the task of elongating the DNA molecule, they also carry out DNA proofreading and repair. DNA Ligase While Helicase works to unwind the DNA molecule, DNA Ligase is the DNA replication enzyme that binds the DNA fragments together by addition of phosphates in the gaps that remain in the phophate-ribose sugar backbone.

DNA Replication Overview Each strand of the DNA double helix has all the information needed to reconstruct the other half by the mechanism of base pairing. Because each strand can be used to make the other strand, they are said to be complementary. A T C G T A A T G C (a) Parent molecule

DNA Replication Overview DNA helicase begins replication by separating the strands and exposing the nucleotide sequence. Primase adds a primer to the DNA molecule to initiate replication DNA polimerases move along the two strands, pairing complementary bases to the exposed nucleotides and proofreads the added segments A T A T C G C G T A T A A T A T G C G C (a) Parent molecule (b) Separation of strands

DNA Replication Overview G C G C G C G T A T A T A T A A T A T A T A T G C G C G C G C (a) Parent molecule (b) Separation of strands (c) “Daughter” DNA molecules, each consisting of one parental strand and one new strand DNA ligase seals up the fragments into one long continuous strand Each original strand joins its complementary strand to form a DNA molecule, resulting in two identical DNA molecules.

DNA Replication Overview