Chapter 8 From DNA to Proteins – Day One

What is DNA? Your “genetic” information (GENES) DNA: Deoxyribonucleic acid DNA is an example of a nucleic acid  which is an organic compound/major macromolecule The monomer (basic building block) of DNA is a nucleotide  many nucleotides join to form a long chain of DNA.

____________________ NUCLEIC ACIDS are built from subunits called ____________________ Image by: Riedell NUCLEOTIDES SUGAR in DNA is ________________ deoxyribose

Overview: Structure of DNA DNA is a long macromolecule made up of units called nucleotides. Each nucleotide is made up of 3 basic parts: a 5-carbon sugar (DEOXYRIBOSE is the sugar in DNA) a phosphate group a nitrogenous base The function of DNA is to store & transmit genetic information!

DEOXYRIBONUCLEIC ACID Image from: ______________ STRANDED Backbone (sides of ladder) made of _____________ and _____________ DOUBLE PHOSPHATES sugars

DNA Structure: What does DNA look Like? Classic Shape: “Double Helix” The backbone/sides of the “ladder” are made up of alternating Sugars (Deoxyribose) & Phosphates. The “steps” or rungs of the “ladder” are made of 4 major Nitrogenous Bases: 1.Adenine3. Cytosine 2.Thymine4. Guanine When looking at the Nitrogen Bases…. – A always pairs with T – G always pairs with C

Structure of DNA: Closer Look There are 4 kinds of nitrogenous bases in DNA  The PURINES (larger, double rings) 1.A = Adenine 2.G = Guanine  The PYRIMIDINES (smaller, single rings) 1.C = Cytosine 2.T = Thymine

Purines (2 rings) Pyrimidines (1 ring) A G C T Phosphate group Deoxyribose sugar Nitrogen bases =“Steps of ladder” Nitrogen bases =“Steps of ladder” © Pearson Education Inc, publishing as Pearson Prentice Hall. All rights reserved

Double Helix A double helix looks like a twisted ladder or spiral staircase – The 2 strands of the double helix are held together by hydrogen bonds between adenine and thymine and between guanine and cytosine A & T always pair C & G always pair – this is known as the principle of complementary base- pairing rules These are known as Chargaff’s rules

DNA is a DOUBLE HELIX X-ray experiments by Rosalind Franklin led James Watson and Francis Crick to the discovery of the structure of DNA in 1953

Rosalind Franklin At the same time of Watson and Crick, Franklin and her aide Maurice Wilkins were studying DNA. They used x-ray crystallography When DNA is bombarded with x- rays, atoms in DNA diffract on the x-rays in a pattern than can be captured on film. Her x-rays showed an “X” surrounded by a circle

James Watson and Francis Crick Double Helix Developed an accurate model of DNA’s three-dimensional model called a double helix Made models of metal and wood to figure out structure of DNA Published their findings in Nature, to show their double helix model – Two strands of DNA wind around each other like a twisted ladder – Strands are complementary

DNA Replication: Why Replicate? In preparation for cell division (during the S Phase of Interphase), a cell must duplicate its genetic info (DNA) to pass on to the new daughter cells.

Overview: DNA Replication Replication copies the genetic information. Watson and Crick’s model suggested a way that DNA could be copied. Single DNA strand can serve as a template, or pattern, for a new strand. – Process by which DNA is copied during the cell cycle is called replication. – Replication assures that every cell has a complete set of identical genetic information. – Remember, DNA is divided into 46 chromosomes that are replicated during the cell cycle.

Overview: DNA Replication 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, the strands are said to be complementary

Duplicating DNA Before a cell divides, it duplicates its DNA in a copying process called replication – During DNA replication, the DNA molecule: 1.Separates into 2 strands 2.Produces 2 new complementary strands following the rules of base pairing Each strand of the double helix of DNA serves as a template, or model, for the new strand

HOW IS DNA COPIED? The structure of DNA explains how it can be copied. Each strand has all the info needed to construct the __________other half. If strands are separated, _____________ rules allow you to fill in the complementary bases. matching base-pairing

Complementary Base Pairing A pairs with T C pairs with G So a complementary strand would look like this – Therefore, the strand AACGTTTTA will replicate as: TTGCAAAAT

Figure 12–11 DNA Replication Growth Replication fork DNA polymerase New strand Original strand DNA polymerase Nitrogenous bases Replication fork Original strand New strand Sites where strand separation and replication occur are called _____________ replication forks

REPLICATION STEPS 1.Enzymes “unzip” molecule by breaking _______________ that hold the strands together and unwind it. 2. _______________ joins nucleotides using original strand as template and ______________for errors. 3. Copying happens in ________ directions along the two strands & in __________ places at once. Hydrogen bonds DNA polymerase spell checks opposite multiple

How Replication Occurs: DNA replication is carried out by a series of enzymes: – These enzymes unwind, unzip, and perform other functions – Each strand then serves as a template for the attachment of complementary bases This is known as a semiconservative process because old strands are used to make new strands The result is 2 DNA strands that are identical, each one having one original strand and one new strand

Duplicating DNA: Visual Overview

DNA Replication Animation DNA Replication Animation Video – YouTube

DNA Replication Animation DNA Replication

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