3.5b DNA structure and replication

POINT > Describe the structure of DNA POINT > Identify the three parts of a nucleotide POINT > Identify the 4 nucleotides in DNA POINT > Explain how the structure of DNA makes replication possible

DNA: Deoxyribonucleic Acid Why is DNA so important? The DNA molecules carry and store the information to build the 1000’s of proteins that cells need to function

POINT > Describe the structure of DNA DNA structure is a double helix

POINT > Identify the three parts of a nucleotide DNA is made of millions of subunits called nucleotides Nucleotides have three parts: 1) a sugar (blue) 2) a nitrogen base -A, G, C, or T (yellow) 3) a phosphate (orange)

CHECK: What are the subunits of DNA called? What are the three parts of a nucleotide?

POINT > Describe the structure of DNA DNA structure is like a twisted ladder The rungs of the ladder are held together by hydrogen bonds (weak) The rungs of the ladder are made of the nitrogen base parts of nucleotides

POINT > Describe the structure of DNA The sides of the ladder are held together by covalent bonds (stronger) The sides of the ladder are made of the sugar and phosphate parts of nucleotides

CHECK: What kind of bond holds the rungs of the DNA ladder together? What part of the nucleotides makes the rungs of the ladder? What kind of bond holds the sides of the ladder together? What part of the nucleotides makes the sides of the ladder? Which is stronger: hydrogen bond or covalent bond?

POINT > Identify the 4 nucleotides in DNA There are four different nucleotides in DNA Adenine (A) Thymine (T) Guanine (G) Cytosine (C)

POINT > Explain how the structure of DNA makes replication possible Adenine always hydrogen bonds with thymine (A-T) Guanine always hydrogen bonds with cytosine (G-C)

CHECK: What is missing? A : T T : A G : C A : T : A C : G : C

POINT > Explain how the structure of DNA makes replication possible Adenine always hydrogen bonds with thymine (A-T) Guanine always hydrogen bonds with cytosine (G-C)

POINT > Explain how the structure of DNA makes replication possible CHECK: How many nucleotides are in this picture?

POINT > Explain how the structure of DNA makes replication possible During DNA replication the two strands separate Then other nucleotides fill in, A with T G with C This creates two new DNA strands

POINT > Explain how the structure of DNA makes replication possible

POINT > Explain how the structure of DNA makes replication possible One DNA molecule Two identical DNA molecules

CHECK: When during the cell cycle does DNA replication happen? During interphase, in S-phase. Where does DNA replication happen? In the nucleus. Why does DNA replication happen? So both daughter cells get a copy of the DNA during cell division.

Homework: Read pages 95-102 Finish Study Guide S.A. page 102 #2 GRAS Pages 50-54 All