Download DNA Replication

How does a baby grow into an adult?
Newborn baby has
between 1 and 5
trillion cells
Grown adult has
between 50 and 100
trillion cells
How does a wound heal?
DNA Replication
and
Cell Division
The importance of cells
• All tissues in our bodies are made up of cells
• Cells must be replicated:
- to support growth (ex: baby to adult)
- to replace damaged or dead cells
(ex: healing a wound or mending broken bones)
DNA – The instructions for life
(Review – don’t copy)
• The cell’s nucleus contains the master set of
instructions that determines:
- what the cell will become & how it will function
• Instructions are carried in chromatin
• Chromatin:
long, thread-like
pieces of DNA,
divided into
segments called
genes
DNA Replication
• Before a cell divides, DNA replication occurs
• The cell makes a copy of every chromatin strand
• Copies are called sister chromatids
DNA Replication
Chromosomes: doubled chromatin strands wind
up, shorten and thicken
Chromatin vs. Chromosomes
DNA replication
DNA
replicates
Mitosis
sister chromatids
• identical strands
centromere
singlestranded
chromatin
May 5, 2017
centromere
doublestranded
chromatin
doublestranded
chromosome
• Humans
have 23 pairs
of chromatin
in each cell
• All 23 pairs
must be
replicated
before cell
division can
take place
Determine all traits
except sex
Determine sex
XX = female
XY = male
Centromere holds
sister chromatids
together
Two copies: sister chromatids
Cell Division
• Once DNA replication is complete, cell division begins
• Two steps:
1) mitosis (4 phase process)
2) cytokinesis
1. Mitosis
• A four phase process in which
the duplicated contents of a cell
divide into two parts.
1. Prophase
2. Metaphase
3. Anaphase
4. Telophase
Your Task:
a) Form groups of 4 students.
b) Each member of the group is to become an
expert on one phase of mitosis by reading
the corresponding pages in your text (p. 34 –
35) and filling in the handout.
c) Teach the other students in your group
about the phase you studied and complete
the handout together.
d) If time permits: Take a set of
images of mitosis from the front
counter and try to put them in the
correct order in your group.
Homework
• Read pages 37-38 (on cytokinesis)
• Mitosis Cut & Paste
Review
• http://iknow.net/player_window.html?url=m
edia/prophase_video_auto.swf&width=360
&height=285
CELL CYCLE – PROPHASE
1.Prophase
centrioles
spindle
fibres
doublestranded
chromosomes
Stages of Mitosis
centrioles move to the opposite ends
of the cell
spindle fibers form between
centrioles
chromatin coils up into chromosomes
nuclear membrane & nucleolus
disintegrate
chromosomes hook onto spindle
fibers by their centromeres
May 5, 2017
CELL CYCLE – METAPHASE
2. Metaphase
centrioles
Stages of Mitosis
spindle fibres shorten or lengthen
pulling chromosomes to align in the
middle (equator) of the cell
sister chromatids
spindle
fibres
May 5, 2017
CELL CYCLE – ANAPHASE
3.Anaphase
Stages of Mitosis
centromeres split & each half pulls
the chromatids to opposite ends
chromosomes are now singlestranded
single-stranded
chromosomes
May 5, 2017
CELL CYCLE – TELOPHASE
4.Telophase
Stages of Mitosis
2 new identical spindle fibres are disassembled
nuclei
centrioles replicate
nucleoli & nuclear membrane
reappear
chromosomes unwind into
chromatin
cytokinesis begins
cytokinesis
May 5, 2017
2. Cytokinesis
• The division of the cell into two daughter cells
• Begins near the end of telophase
Cytokinesis in animal cells
• Ring of specialized proteins at middle of cell start to
contract
• Pinches cell membrane until parent cell becomes
two daughter cells
• Each daughter cell has cytoplasm, organelles &
complete set of chromosomes in a nucleus
Contraction of
proteins and
pinching of
membrane
Two daughter
cells produced
Cytokinesis in plant cells
• Golgi body produces small vesicles that carry
materials to make new cell wall
• Vesicles line up at centre of cell forming cell plate
• Cell plate grows out to meet old cell wall
 new wall formed separating two daughter cells
Comparing cytokinesis in animal and plant cells
Homework
• Stages of Cell Cycle Worksheet