Upload
others
View
3
Download
0
Embed Size (px)
Citation preview
Cell Growth and Division
Chapter 5
THE CELL CYCLE
5.1
Where it all began…
• You started as a cell smaller than a period at the end of a sentence…
And now look at you!!
Getting from there to here…
• Going from egg to baby…. the original fertilized egg has to divide…
and divide… and divide… and divide…
Why do cells divide?
• For reproduction – asexual reproduction
• one-celled organisms
• For growth – from fertilized egg to
multi-celled organism
• For repair & renewal – replace cells that die
from normal wear & tear or from injury
Key Concept
• Cells have distinct phases of growth, reproduction, and normal functions
The Cell Cycle
• Is a regular pattern of growth, DNA replication, and cell division
4 Main Stages
• Gap 1 (G1): – cell growth and normal
functions • DNA synthesis (S):
– copies DNA • Gap 2 (G2):
– additional growth • Mitosis (M):
– division of the cell nucleus (mitosis) and division of the cell cytoplasm (cytokinesis)
Cell Division Rates
• Rate of cell division varies with the need for those types of cells
Cell Size
• Cell size is limited – cells can only get so big!
– surface area: volume ratio is important
Surface Area
• Must allow for adequate exchange of materials – cell growth is coordinated with division
– cells that must be large have unique shapes
MITOSIS AND CYTOKINESIS
5.2
Key Concept
• Cells divide during mitosis and cytokinesis
Mitosis
• Chromosomes condense at the start of mitosis – DNA wraps around proteins
DNA double helix
DNA and histones
Chromatin Supercoiled DNA
C-words
• DNA + proteins = chromatin
• ½ chromosome = chromatid
• Sister chromatids held together by a centromere
Goal of Mitosis
• To produce two genetically identical daughter cells
• Interphase – prepares the cell
for division
– DNA is duplicated
Prophase
• Chromosomes condense and spindle fibers form
Metaphase
• Chromosomes line up in the middle of the cell
Anaphase
• Sister chromatids separate to opposite sides of the cell
Telophase
• The new nuclei form and chromosomes begin to uncoil
Cytokinesis
• In animal cells, the membrane pinches closed
• In plant cells, a cell plate forms
REGULATION OF THE CELL CYCLE
5.3
Key Concept
• Cell cycle regulation is necessary for healthy growth
Factors to Regulate Cell Division
• External factors: – physical and chemical signals
– Ex: contact inhibition
Factors to Regulate Cell Division
• Internal factors: – kinases (enzymes)
– cyclins (protein involved in the progression of cells through the cell cycle)
Apoptosis
• Programmed cell death – a normal
feature of healthy organisms
– a cell produces self-destructive enzymes
– occurs in development of infants
webbed fingers
Cancer
• Uncontrolled cell division
• Cancer cells form disorganized clumps (tumors) – Benign tumors remain clustered and can be
removed.
– Malignant tumors metastasize, or break away, and can form more tumors
Cancer
• Cancer cells do not carry out necessary functions.
• Cancer cells come from normal cells with damage to genes involved in cell-cycle regulation
Carcinogens
• Substances known to cause cancer
• Standard cancer treatments typically kill both cancerous and healthy cells
ASEXUAL REPRODUCTION
5.4
Key Concept
• Many organisms reproduce by cell division
Binary Fission
• Similar to mitosis
• Asexual reproduction
• Creation of offspring from one parent – produces two
daughter cells genetically identical to the parent cell
– occurs in prokaryotes
parent cell
DNA duplicates
cell begins to divide
daughter cells
Environment vs. Reproduction
• Environment determines what form of reproduction is most advantageous
• Asexual reproduction – an advantage in
consistently favorable conditions
• Sexual reproduction – an advantage in changing
conditions
Budding
• Forms a new organism from a small projection growing on the surface of the parent
bud
Hydra
Yeast
Fragmentation
• The splitting of the parent into pieces that each grow into a new organism
MULTICELLULAR LIFE
5.5
Key Concept
• Cells work together to carry out complex functions
Multicellularity
• Multicellular organisms depend on interactions among different cell types
CELL TISSUE ORGAN
Specialized Cells
• Cell differentiation – cells developing into their mature forms
– different genes are expressed
Outer: skin cells Middle: bone cells Inner: intestines
Stem Cells
• Unique body cells
• Have the ability to: – divide and renew themselves
– remain undifferentiated in form
– develop into a variety of specialized cell types
Stem Cells, 3 types
Stem Cells
• Come from adults and embryos
• Adult stem cells: – hard to isolate and
grow – may prevent
transplant rejection
• Embryonic stem cells: – raises ethical issues – can be grown
indefinitely in culture
Stem Cells Uses
• Treat leukemia and lymphoma
• May cure disease or replace damaged organs
• May revolutionize the drug development process