DNA and Cell Reproduction

1
DNA and Cell Reproduction

• Chapters 10 and 8

2
Structure of DNADeoxyribonucleic 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.

10
(No Transcript)
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
• 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