cell growth and divisionjkilfoyle.weebly.com › uploads › 1 › 2 › 2 › 8 › 12288004 ›...
TRANSCRIPT
![Page 1: Cell Growth and Divisionjkilfoyle.weebly.com › uploads › 1 › 2 › 2 › 8 › 12288004 › 5... · Chapter 5 . THE CELL CYCLE 5.1 . ... ASEXUAL REPRODUCTION 5.4 . Key Concept](https://reader033.vdocuments.net/reader033/viewer/2022060500/5f1a0b8396c1ad4a9d27ac16/html5/thumbnails/1.jpg)
Cell Growth and Division
Chapter 5
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THE CELL CYCLE
5.1
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Where it all began…
• You started as a cell smaller than a period at the end of a sentence…
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And now look at you!!
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Getting from there to here…
• Going from egg to baby…. the original fertilized egg has to divide…
and divide… and divide… and divide…
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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
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Key Concept
• Cells have distinct phases of growth, reproduction, and normal functions
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The Cell Cycle
• Is a regular pattern of growth, DNA replication, and cell division
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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)
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Cell Division Rates
• Rate of cell division varies with the need for those types of cells
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Cell Size
• Cell size is limited – cells can only get so big!
– surface area: volume ratio is important
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Surface Area
• Must allow for adequate exchange of materials – cell growth is coordinated with division
– cells that must be large have unique shapes
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MITOSIS AND CYTOKINESIS
5.2
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Key Concept
• Cells divide during mitosis and cytokinesis
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Mitosis
• Chromosomes condense at the start of mitosis – DNA wraps around proteins
DNA double helix
DNA and histones
Chromatin Supercoiled DNA
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C-words
• DNA + proteins = chromatin
• ½ chromosome = chromatid
• Sister chromatids held together by a centromere
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Goal of Mitosis
• To produce two genetically identical daughter cells
• Interphase – prepares the cell
for division
– DNA is duplicated
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Prophase
• Chromosomes condense and spindle fibers form
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Metaphase
• Chromosomes line up in the middle of the cell
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Anaphase
• Sister chromatids separate to opposite sides of the cell
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Telophase
• The new nuclei form and chromosomes begin to uncoil
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Cytokinesis
• In animal cells, the membrane pinches closed
• In plant cells, a cell plate forms
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REGULATION OF THE CELL CYCLE
5.3
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Key Concept
• Cell cycle regulation is necessary for healthy growth
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Factors to Regulate Cell Division
• External factors: – physical and chemical signals
– Ex: contact inhibition
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Factors to Regulate Cell Division
• Internal factors: – kinases (enzymes)
– cyclins (protein involved in the progression of cells through the cell cycle)
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Apoptosis
• Programmed cell death – a normal
feature of healthy organisms
– a cell produces self-destructive enzymes
– occurs in development of infants
webbed fingers
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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
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Cancer
• Cancer cells do not carry out necessary functions.
• Cancer cells come from normal cells with damage to genes involved in cell-cycle regulation
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Carcinogens
• Substances known to cause cancer
• Standard cancer treatments typically kill both cancerous and healthy cells
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ASEXUAL REPRODUCTION
5.4
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Key Concept
• Many organisms reproduce by cell division
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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
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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
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Budding
• Forms a new organism from a small projection growing on the surface of the parent
bud
Hydra
Yeast
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Fragmentation
• The splitting of the parent into pieces that each grow into a new organism
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MULTICELLULAR LIFE
5.5
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Key Concept
• Cells work together to carry out complex functions
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Multicellularity
• Multicellular organisms depend on interactions among different cell types
CELL TISSUE ORGAN
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Specialized Cells
• Cell differentiation – cells developing into their mature forms
– different genes are expressed
Outer: skin cells Middle: bone cells Inner: intestines
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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
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Stem Cells, 3 types
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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
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Stem Cells Uses
• Treat leukemia and lymphoma
• May cure disease or replace damaged organs
• May revolutionize the drug development process