1. DNA and Cell Reproduction

2. Structure of DNA Deoxyribonucleic Acid
DNA is one of the two nucleic acids
DNA
RNA
It is composed of repeating subunits (monomers) called NUCLEOTIDES.
A nucleotide has three components
– deoxyribose sugar
A phosphate
A nitrogenous base

3. Nitrogenous Bases Adenine (A) Guanine (G) Cytosine (C) Thymine (T)
These are grouped into
Purines – two carbon rings (A and G)
Pyrimidines – one carbon ring (T and C)

4. The Double Helix
A always pairs with T
C always pairs with G

5. DNA Replication
1. Helicase enzymes cause the strands to unwind and separate. (The point where the two chains separate is the replication fork.)
2. DNA polymerases bind to each chain of DNA.
3. The DNA polymerase moves along the chain and aids in the addition of nucleotides for the formation of the new chain.

6. DNA replication does not begin at one end of the molecule and proceed to the other end. DNA replication occurs in many points simultaneously along the molecule.

7. Accuracy and Repair
DNA replication is very accurate – about 1 error in every 10,000 paired nucleotides.
DNA has the ability to proofread and repair mistakes.
An error in replication is known as a MUTATION.
DNA may also be damaged by a variety of agents which include chemicals and ultraviolet light.

8. What is an enzyme? An enzyme is a catalyst that is usually an protein.
Enzymes are substrate specific.
They have a lock and key fit.
Allow reaction in living organisms to occur at lower temperatures by reducing the activation energy.
Usually end in –ase and identify the substrate the work on. Example: proteases, nucleases

9. Chromosomes are Composed of DNA
DNA in humans is about 6 billion pairs of nucleotides and is located in the nucleus as chromosomes.
Each chromosome is a single DNA molecule associated with protein.
DNA in eukaryotes wraps tightly around proteins called HISTONES.
A chromosome consists of two identical halves called chromatids.

11. The consticted area of each chromosome is called a chromatid (a protein disk),
Between cell divisions, the DNA is not so tightly wound and is called chromatin.
Centromere
chromatid

12. Each species has a characteristic number of chromosomes – see pate 146.
Human and animal chromosomes are categorized as sex chromosomes or autosomes.
Sex chromosomes determine the sex of the organism
Autosomes are all other chromosomes
Every cell has two copies of autosomes. These copies are called homologous chromosomes

13. HOMOLOGOUS CHROMOSOMES
SAME SIZE
SAME SHAPE
SAME GENES FOR THE SAME TRAITS
Homologous chromosomes may be arranged in order to form a karyotype.

14. Karyotype

15. Diploid – having two sets of chromosomes
Both chromosomes of the homologous pair
Both of the sex chromosomes
Haploid – having only one set of chromosomes
Half of the chromosome number
One chromosome of the homologous pair
Only one sex chromosome

16. Cell Division Eukaryotes Prokaryote Membrane bound organelles
DNA is in chromosomes
Two processes for cell division
Mitosis
Meiosis
Prokaryote
No membrane bound organelles
Only one circular chromosome
Reproduce by binary fission

17. The Cell Cycle