The document discusses the process of cell division, including the two main types (mitosis and meiosis). It explains DNA structure and replication, the stages of mitosis (prophase, metaphase, anaphase, telophase), and the cell cycle stages of interphase and the M phase. The goal of cell division is to make copies of cells for growth, tissue repair, and reproduction.

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.