DNA Structure and Replication

DNA Structure (reading handout)

·      DNA’s shape is known as a double helix (it looks like a twisted ladder)

·      DNA’s main building piece is a nucleotide

·      Each nucleotide is made of a deoxyribose (sugar), phosphate and a nitrogen base.

·      The nucleotides connect in two places:

o       Between the phosphate and the sugar

o       Between the nitrogen bases

·      The “uprights” or sides of the DNA ladder are made of deoxyribose and phosphate

·      The “rungs” of the DNA ladder are made of nitrogen bases

·      The four types of nitrogen bases are:

o       adenine

o       thymine

o       cytosine

o       guanine

DNA Replication (pages 78-79)

• DNA replication needs to happen so that each daughter cell has an exact copy of the genetic information 

The Structure of DNA (page 78)

• DNA is in the shape of a twisted ladder known as a double helix
• Nitrogen base pairs form the rungs of the ladder
• In the base pairs, adenine (A) matches with thymine (T) and guanine (G) matches with cytosine (C)

The Replication Process (page 79)

• To replicate, DNA pulls apart between the base pairs
• New bases in the nucleus match up in the same A-T and G-C pairs
• The order in the new DNA molecule should exactly match the order in the old DNA molecule

Cell Division

Chapter 2, Section 5

Pages 72-79

Make sure you know the following vocabulary:

1. fertilization
2. mitosis
3. chromosome
4. interphase
5. cytokinesis
6. replication

The Cell Cycle (page 73)

• In order to divide, cells need to either know how to make new cell parts, or divide cell parts evenly between the two new cells
• The cell cycle is the regular pattern of growth and division that a cell goes through

Stage 1: Interphase (pages 73-74)

• Interphase is the stage before the cell divides
• During this time the cell
• grows
• replicates its DNA
• prepares to divide into two new cells

 Growth (page 73)

• During this time, the cell grows to its full size
• The cell also produces all cell organelles needed

 DNA Replication (page 73)

• DNA is copied during replication
• Without a complete new copy of DNA, a cell cannot survive
• At the end of replication, two copies of DNA (one for each new cell) are ready 

Preparation for Division (page 74)

• During this time the cell produces structures needed for division

Stage 2: Mitosis (page 74)

• Mitosis is the stage where the cell’s nucleus divides into two new nuclei
• During mitosis each nucleus receives a copy of the DNA
• There are four steps to mitosis
• prophase-
• chromatin in the cell’s nucleus condenses
• a double rod of chromatin is a chromosome
• metaphase-
• chromosomes line up in the middle of the cell
• thread-like structures attach
• anaphase-
• the chromosome is split in half and move towards the edge of the cell
• telophase
• chromosomes reach the edges of the cell
• a nuclear membrane is formed around each set of chromosomes 

Stage 3: Cytokinesis (page 75)

• The cytoplasm divides to form two new cells

Length of the Cell Cycle (page 75)

• The length of a cell cycle depends on the organism