1. Chapter 8
Cell Division
By Mr. “4 weeks” Chapman

2. Cell Division
 What is cell division?
 Is how a cell
reproduces, makes a
copy of itself.
 Is how living things grow
and make sex cells.

3. Why do we need new cells???
 Need new cells to grow, repair scratches and
tears (scar).

4. Cell Division
 2 Types of Cell
Division
 1. Mitosis – process of
making new somatic
(nonsex) cells like skin
cells (clones).

5. Cell Division
 2. Meiosis – process of
making new sex cells
(gametes) like sperm
and egg (23
chromosomes).

7. Nucleic Acid
 2 types of Nucleic Acids:
 1. DNA
 2. RNA

8. Nucleic Acids
 Function of DNA –
 Store and transmit hereditary information
 DNA – Deoxyribose nucleic acid
 Has 2 strands

9. DNA Structure
 DNA is made out of 2
long chains of
nucleotides.
 4 Types of nucleotides:
 Adenine (A)
 Guanine (G)
 Cytosine (C)
 Thymine (T)

10. Structure of Nucleotides
 Nucleotides are made out of 3 molecules:
 1. deoxyribose – sugar molecule
 2. phosphate group – contains phosphate (P)

11. Nucleotide Structure
 3. Nitrogen base – contains nitrogen (N)
 Adenine (A)
 Guanine (G)
 Cytosine (C)
 Thymine (T)

12. Nucleotide

13. DNA
 The DNA molecule model was proposed
by James Watson and Francis Crick.

14. Double Helix
 Complementary
Base Pairing:
certain bases
always pair with
each other
 A with T
 G with C

15. DNA Replication
 Replication of DNA:
 DNA unwinds and
Helicase (enzyme)
breaks apart the 2
strands.
 Each strand serves
as a template for the
new DNA

16. DNA Replication
 DNA polymerase:
(enzyme) that adds
nucleotides to each
strand of DNA.
 Many polymerases
attach at the same
time.
 On a fruit fly DNA
replication starts at
6,000 different places

18. DNA Replication
 According to the base pairing rules, what
would the new stand of DNA be if the
original strand was
 A – T – T – C – C- G

19. DNA Replication
 Accuracy and Repair
 DNA is copied with a high degree of
accuracy
 Mutation: change in the nucleotide
sequence of DNA; it can have serious
effects on the organism.
 Can be harmful or beneficial

20. DNA Replication
 Environmental factors can damage DNA
 Ex. Ultraviolet radiation from the sun,
enzymes work to repair the damaged DNA
 What do you think would happen if the
repair enzymes weren’t working
properly?

21. Cell Division
 Now you know what DNA is…… how
does the cell organize DNA for Mitosis.

22. Cell Division
 Chromosomes – tightly coiled  Strands of DNA wrap
packages of DNA; they are rod around proteins called
shaped and proteins hold them Histones.
together.

24. Cell Division
 Chromatid – half of a
chromosome; forms as
DNA copies itself before
cell division
 Centromere – holds the
chromatids together until
they separate

26. Important Words
 How many chromosomes
do humans have?
 Each species has a unique
number of chromosomes.  46 chromosomes or 23
pairs.

28. Types of Chromosomes
 2 Types of Chromosomes:
 1. Sex Chromosomes – are the chromosomes that
determine the sex of an organism.
 Female: XX
 Male: XY
 2. Autosomes – all other chromosomes
 Humans: 44 autosomal chromosomes

30. Chromosomes
 Homologous chromosomes – two
copies of each autosome (maternal and
paternal)
 Homologous chromosomes are the
same size, shape, and carry genes for
the same trait.

32. Chromosomes
 Karyotype – is a picture
of the chromosomes in
a dividing cell.
 22 homologous pairs
of autosomes.
 2 sex chromosomes

34. Chromosomes
 Diploid (2n)– cells have two sets (maternal
and paternal) of chromosomes.
 Has all 46 chromosomes.
 Haploid (n)– cells have one set of
chromosomes.
 Has 23 chromosomes.
 Gametes

35. Chromosomes
 Examples of haploid
cells?
 Gametes - sperm and
egg cells; they have 23
chromosomes
 Fertilization 23 in
sperm + 23 in egg =
46

36. Cell Division
 Where do new cells come from?
 All cells came from preexisting cells.
 Why do cells divide?
 1. Increase Cell volume
 2. Growth
 3. Repair tissue and organs
 4. Reproduce

37. Cell Division
 Prokaryotes – cell division by:
 Binary Fission  DNA copied, cell grows, cell
splits in two.
 Eukaryotes – cell division by 2 ways:
 Mitosis  new cells have identical genetic
material; produces clones.
 Meiosis  reduces chromosome number in
half, makes sex cells (gametes).

38. Cell Cycle
 The Cell Cycle – a
repeating set of events
that make up the life of a
cell.
 There are 3 steps to the
cell cycle.

39. Cell Cycle
 1. Interphase – the longest phase, in between cell
division
 G1 phase – growth of cell
 G0 phase – inactive stage.
 S phase – DNA is copied (“S” synthesis of DNA)
 G2 phase – growth of cell; prepares for cell division
 *G0 phase – non dividing state after the G1 phase;
 Ex. Many cells in human body – nervous system cells

41. Mitosis
 2. Mitosis – division of the nucleus; a continuous
process divided into 4 phases
 1. Prophase
 2. Metaphase
 3. Anaphase
 4. Telophase
 3. Cytokinesis – division of the cytoplasm
 The chromosomes start to uncoil and become less dense
 Two new, identical cells are formed

42. G1 phase
M phase
S phase
G2 phase

43. Cell Mitosis (M Phase)
 The many stages of the
cell life cycle can be
seen in the image to the
right
 The process of cell
reproduction includes
prophase, metaphase,
anaphase, and
telophase

45. Mitosis
 1. Prophase
 Chromosomes
appear
 The nucleolus
disappears
 The nuclear
membrane begins to
break down

46. Mitosis
 2. Metaphase
 Chromosomes align
along the equator of
the cell
 Spindles Fibers that
are attached to the
poles connect to the
centromeres

47. Mitosis
 3. Anaphase
 Chromosomes are
pulled to the pole by
the contraction of the
spindle fibers
 Sister chromatids are
separated at the
centromere

48. Mitosis
 3. Anaphase (Late)
 Chromosomes begin
to congregate at the
poles.

49. Mitosis
 4. Telophase
 The new cell wall
begins to form so the
two cells can
separate
 The chromosomes
begin to form a
nucleus.
 See cleavage
(animal) and Cell
plate (plant) cells.

50. Cytokenisis

51. What are the phases?
Interphase Prophase Prometaphase

52. What are the phases?
Anaphase Telophase/
Metaphase
Cytokenisis

53. What stage of Mitosis?

54. DNA (Double Helix)
 Transcription – process of turning DNA
into RNA
 Translation – process of using RNA to
make protein.
 DNA has 2 strands
 RNA has 1 strand.