Download Cell Size Continued

Chapter 9
Cell Reproduction
Review:
What we know
• Cells have DNA /
genetic information
• We pass on our info to
our children
• All our cells contain
DNA
• Chromosomes are
bundles of DNA
What we need know
• How do our cells make new
cells?
• What can go wrong?
• Do all cells get made the
same?
• Can do bacteria and viruses
make new cells?
In the beginning…
• You start life as a single
cell
Human Embryo
Day 3
Human Embryo
20 Weeks
Until the end of time…
• New cells made
throughout entire life
• Called cell reproduction
Cell Reproduction
• Goal:
– Replace old or worn out
cells
– Growth & Development
Cell Size
• Most cells are less than 100
micrometers
–Smaller than a period . at the end
of a sentence!
• Why?
–To ensure that the needs of the
cell are met.
http://learn.genetics.utah.edu/content/begin/cells/scale/
Cell Size Continued:
• Factors that influence cell size are:
–Ratio of surface area to volume
• Surface area is the area covered by
the plasma membrane
(nutrients & wastes
must pass through)
SA = L x W x # sides
Cell Size Continued:
• Volume is the space taken by the
inner contents of the cell
(including organelles and nucleus)
V=LxWxH
Cell Size Continued:
• As cell grows the ratio of surface
area to volume will continue to
decrease!
• Volume increases much more
rapidly than the surface area!
Cell has TROUBLE:
- supplying nutrients
- expelling waste products
Cell Size Continued:
• SMALL cells have a higher ratio &
can sustain themselves!
REMEMBER:
How do substances move in a cell?
Cell Size Continued:
• Communication breaks down over
long distances!
Investigate Cell Size:
• Complete the
Investigation
of Cell Size by
creating a
table on your
handout.
Hypothetical SA V SA:V
Cells
Ratio
0.00002 m
0.001 m
2.5 m
30 cm
15 m
Investigation of Cell Size:
So based on your calculations do
cells become large?
Are large organisms large because
they contain extra large cells or
just more standard – sized cells?
Cell
Cycle
AKA
A Cell’s
Life
Cell Cycle
• Once cell reaches a certain size it
must:
–Stop growing or
–Divide
• The cell cycle is a cell’s cycle of
growing and dividing.
• One complete cycle produces two
cells.
Cell Cycle
• When repeated continuously the
result is a continuous production
of NEW cells!
3 Main Phases of Cell Cycle:
• Interphase
– Cell grows, carries our cellular
functions, & replicates (makes
copies) of DNA
• Mitosis
– Cell’s nucleus and nuclear material
divide
• Cytokinesis
– Cell’s cytoplasm divides creating a
new cell
Interphase:
• Divided into 3 stages:
– G1
• Cell grows, carries out normal cell
functions, prepares to replicate
DNA.
• Checkpoint for size & nutrients!
Interphase continued:
–S (aka the synthesis phase)
• Cell copies (replicates)
its DNA to prepare for
cell division
Interphase continued:
–G2
• Cell prepares for the division of
its nucleus
• Checkpoint to make sure cell is
ready for mitosis!
M Phase of Cell Cycle
a.k.a. Mitosis
• Result = two identical cells
• Forms all human body cells
• Ex: skin, blood,
bones, stomach
• Slows with age
Different Forms of DNA:
• Remember DNA is found in
the nucleus
• DNA  Deoxyribonucleic
Acid
• In it’s normal state DNA is
loosely coiled and in the
form of chromatin.
Chromatin:
• Looks like loose spaghetti!
Chromosomes:
• During what phase is DNA
replicated? “S” phase of
Interphase.
• Humans have 46
chromosomes or 23 pairs:
–23 from mom
–23 from dad
Chromosomes:
• Once copied the DNA will
begin to coil tightly
around proteins and is
now called chromosomes.
Chromatid (s):
• The chromosomes 1-23 from
mom will then pair up with
chromosome 1-23 from dad
respectively!
Chromatid (s):
• Once chromosomes are
paired they are now called
sister chromatids.
• Each half is a chromatid but
together they are sister
chromatids.
Chromatid


Chromatid
Centromere:
• Each sister chromatid is
held together by a
centromere!
Remember Before Cells
Divide
• DNA replication occurs 
chromosomes double
• This stage of the cell
cycle is called interphase
Interphase
• Longest stage
of cell cycle
• Cell is preparing for
mitosis
• Cell gets larger &
centrioles double
Interphase
Interphase (cont.)
Plant Cells in Interphase
Plant Cell in Interphase (cont.)
Stages of Mitosis
P–M–A–T
PROPHASE
• Chromosomes shorten & thicken
(shaped like an X)
–Each half = chromatid
–Attached by centromere.
• Nuclear membrane breaks down
• Centrioles move apart
• Spindle fibers form between
centrioles
Prophase
Plant Cell in Early Prophase
Plant Cell in Late Prophase
METAPHASE
• Centrioles move to opposite
sides of cell
• Spindle fibers stretch
between centrioles
• Chromosomes line up in the
middle by fibers connected
to the centromere
METAPHASE (cont.)
• Sister chromatids are
pulled to line up at center
of cell
• “Meta-” Prefix
meaning middle
Centromere
• Part that holds
chromosomes
together
Plant Cell in Metaphase
Plant Cell in Metaphase
ANAPHASE
• Sister chromatids are
pulled apart
• Fibers pull
chromatids
toward
centrioles
Anaphase
Plant Cell in Anaphase
Plant Cell in Anaphase
TELOPHASE
• Fibers begin to disappear
• Nuclear membrane begins
to reform
• Cell membrane pinches in
Plant Cell in Telophase
Cytokinesis
• Last stage of cell
cycle
• Process of
dividing the
cytoplasm
• Starts during
anaphase
finishes after
telophase
In the end…
• Each cell has a complete
set of chromosomes
• Two identical daughter
cells  formed from one
parent cell
Mitosis Completed
http://www.edumedia-sciences.com/en/a70-mitosis
Changes in Rate of Mitosis
• Cancer: Cells divide at a
fast rate  out of control
• Malignant: dangerous
• Benign:
not dangerous
Abnormal Cell Division
• A tumor is a mass of tissue
that results from excessive
cell division
Apoptosis:
• Not every cell is destined to
survive!
• Some cells go through
programmed cell death called
apoptosis.
–Cell shrinks & shrivels
All animal cells have a “death
program” that can be activated.
Stem Cells
• Discovered in 1998
• Unspecialized cells that can develop
into specialized cells under the right
conditions.
• Two types:
– Embryonic stem cells
– Adult stem cells
How other cells divide
1.Bacteria (Prokaryote)
One cell splits into two
Asexual
reproduction
Same genes as
“parent”
Bacteria Cell Reproduction
How other cells divide (cont.)
2.Viruses – Inject
their DNA into
other cells
Not considered
“living” cells
Viral Cell Reproduction
Step 1
Step 3
Step 2
Step 4