DNA Structure and Replication Chapter 9, pgs

What is DNA? Deoxyribonucleic Acid Deoxyribonucleic Acid Contains genetic information for all living things(acts as blueprint or code). Contains genetic information for all living things(acts as blueprint or code). Found in nucleus of cell. Found in nucleus of cell. Shape is double helix – looks like twisted ladder or twisted zipper. Shape is double helix – looks like twisted ladder or twisted zipper.

DNA is a polymer made of repeating subunits called nucleotides. DNA is a polymer made of repeating subunits called nucleotides. Nucleotides have three parts: a sugar, a phosphate group, and a nitrogenous base. Nucleotides have three parts: a sugar, a phosphate group, and a nitrogenous base. Backbone or sides of ladder are the sugar (deoxyribose) and phosphate group. Backbone or sides of ladder are the sugar (deoxyribose) and phosphate group. Rungs of the ladder or middle is the bases. Rungs of the ladder or middle is the bases. Structure

In DNA, there are four possible nitrogenous bases: adenine (A), guanine (G), cytosine (C), and thymine (T). In DNA, there are four possible nitrogenous bases: adenine (A), guanine (G), cytosine (C), and thymine (T). Adenine (A)Guanine (G) Thymine (T) Cytosine (C )  Bases put into 2 categories.  Purines: A and G  Pyrimidines: T and C (both contain Y)

Base Pairing Rule Always Together Adenine always pairs with Thymine forms 2 hydrogen bonds with each other Cytosine always pairs with Guanine forms 3 hydrogen bonds with each other

Amount of adenine always equal to amount of thymine. Amount of adenine always equal to amount of thymine. Amount of guanine always equal to amount of cytosine. Amount of guanine always equal to amount of cytosine. Each strand is complementary Each strand is complementary sequences on one strand determines sequence on the other. sequences on one strand determines sequence on the other. Complementary base pairs

What is the complementary strand? AGTACCGATACGGAATAGC AGTACCGATACGGAATAGC GGTTACATAAATCGGTACC GGTTACATAAATCGGTACC TACCGGAGTAGCATTACTT TACCGGAGTAGCATTACTT CATTACCCAATGGACGTTA CATTACCCAATGGACGTTA

DNA Replication Process where DNA makes an identical copy of itself. Process where DNA makes an identical copy of itself. During Cell division, DNA coils into 46 chromosomes= 23 pairs, one from mom and one from dad. During Cell division, DNA coils into 46 chromosomes= 23 pairs, one from mom and one from dad. Chromosomes are DNA and proteins called histones. Chromosomes are DNA and proteins called histones. Tightly packed DNA and proteins form chromatin Tightly packed DNA and proteins form chromatin During mitosis, chromatin condenses to form tightly packed chromosomes During mitosis, chromatin condenses to form tightly packed chromosomes

Figure Chromosome Structure of Eukaryotes Chromosome Supercoils Coils Nucleosome Histones DNA double helix Section 12-2 Go to Section:

Section 11.1 Summary – pages Replication of DNA DNA Replication Step 1. An enzyme, DNA helicase, unzips DNA molecule. Step 2. Another enzyme, DNA polymerase, adds complementary base pairs to each side of the separated strands producing two identical DNA molecules.

Replication occurs in the 5’ prime to 3’ prime direction. DNA polymerase (the enzyme responsible for replication) can only add a new nucleotide onto the 3' end of an existing strand

Proofreading DNA DNA polymerase’s job is also to check its work as it copies the DNA strand. DNA polymerase’s job is also to check its work as it copies the DNA strand. If it mismatches a nucleotide, it backs up and fixes mistake If it mismatches a nucleotide, it backs up and fixes mistake WHAT HAPPENS IF A MISTAKE IS MADE? WHAT HAPPENS IF A MISTAKE IS MADE? Mutations- Change in the sequence of the DNA Mutations- Change in the sequence of the DNA

Discovery 1949: biochemist Chargaff observed that in DNA, A=T and G=C. 1949: biochemist Chargaff observed that in DNA, A=T and G=C. 1953: Rosalind Franklin took X-ray of DNA. 1953: Rosalind Franklin took X-ray of DNA. From X-ray, Watson and Crick developed model of DNA helix. From X-ray, Watson and Crick developed model of DNA helix.