1. Introduction to the Cell Cycle & DNA
Human Biology
Introduction to the Cell Cycle & DNA
Maui Papaya Truck

2. Cell Reproduction
Cells reproduce by dividing in two. This is why we alternatively use the term “cell division.”
Cell reproduction is a defining feature of life.
Mechanisms of cell reproduction are the same for all eukaryotes although some variations occur due to specialization of the 200 types of specialized cells in humans.
Many familiar cell structures and regulation necessary
2.4 million new erythrocytes are produced per second!
Energy! Materials!

3. MITOTIC PHASE INTERPHASE
Mitosis
Nucleus divides
Cytokinesis
Cell divides
MITOTIC
PHASE M G2 G1
Cell prepares
for division.
Growth continues
slowly.
Primary period
of cell growth. S
DNA is duplicated.
Growth continues
slowly. G0
INTERPHASE
Figure 17.1

4. The Cell Cycle Creates New Cells Step by Step
Interphase
Long growth period between cell divisions
G1 (gap 1)
primary growth phase, very active growth
S (synthesis)
synthesis of DNA for next cell division
G2 (gap 2) final growth phase before cell division
Mitotic phase (cell division phase)
Mitosis
Nuclear division
duplicated DNA is distributed between two daughter nuclei, nucleus divides
Cytokinesis
Cytoplasm divides, two new daughter cells are formed

5. DNA, Genes & Chromosomes
DNA replication
Process of copying DNA prior to cell division
Gene
Short segment of DNA that contains the code, or recipe, for a protein or for enzymatic RNA
Smallest functional unit of DNA
Chromatin
Threadlike combination of DNA and histone proteins present in interphase cells (preparing for division) or in resting cells (taking a break from division)
Chromosome
Rod-like structure of highly coiled chromatin in cells in the mitotic phase of cell division

6. DNA to Chromosome Double-stranded DNA Histones Chromatin material:
not visible
during
Interphase
One chromatid
Its sister
chromatid
Centromere
Chromosome: visible during mitosis

7. Replication, Transcription & Translation: Overview
Process of copying DNA information of a gene into mRNA (messenger ribonucleic acid)
Occurs within the cell nucleus
Translation
Process of converting the mRNA code into one or more proteins
Occurs in the cytoplasm at ribosomes

8. double-stranded DNA to a single-stranded mRNA
Replication
Produces an exact
copy of DNA
Occurs prior to
every cell division
DNA
Transcription
Converts a portion of
double-stranded DNA to a
single-stranded mRNA
Occurs within the nucleus
mRNA
Translation
Converts an mRNA
code into one or
more proteins
Takes place in the cytoplasm
Protein
Figure 17.3

9. Replication: Copying DNA Before Cell Division
DNA strands uncoil and “unzip”
Each single strand serves as a template for the creation of a new complementary strand
DNA nucleotides are positioned and linked by DNA polymerase
Precise base-pairing (A with T & C with G) assures that an exact copy is made (mistakes corrected?)

10. Keys:
= Cytosine
= Adenine
= Guanine
= Thymine
Parent strand
New
(daughter)
strands
forming
Parent strand
The double-stranded DNA unwinds, and each single
strand serves as a template for a new complementary
strand.

11. Replication
bubble
Parent
strands
New
complementary
strands
Parent DNA
molecule
2 complete
daughter DNA
molecules
The unwinding and the formation of new strands occur simultaneously at many sites on the DNA molecule. The sites of replication expand outward until they join. For simplicity the two strands are shown as parallel in (b), but in actuality they form a helical shape.

12. Replication: Mutations
Alterations or “mistakes” in the DNA code
Occur most frequently during DNA replication
Causes: Chemical and physical forces
Mutations can be:
Silent—have no effect
Deleterious—harmful, may result in cell death or cancer
Beneficial—basis for evolution
Some mutations are repaired by repair enzymes
The higher the rate of replication, the higher the mutation rate.