i. the cell cycle
DESCRIPTION
I. The Cell Cycle. There are three stages to the cell cycle: Interphase -G1 (growth) -S (DNA Replication) -G2 (growth and addition of organelles) Mitosis -Prophase -Metaphase -Anaphase -Telophase 3. Cytokinesis. I. The Cell Cycle. - PowerPoint PPT PresentationTRANSCRIPT
I. The Cell Cycle
• There are three stages to the cell cycle:1. Interphase
-G1 (growth)-S (DNA Replication)-G2 (growth and addition of organelles)
2. Mitosis-Prophase-Metaphase-Anaphase-Telophase
3. Cytokinesis
I. The Cell Cycle• The Cell cycle
represents the time it takes for a cell to grow, reproduce, and divide
• Some cells go through the Cell Cycle much quicker than others
A. Interphase
• Interphase is the longest part of the cell’s life
• Some cells (muscle and nerve cells) remain in interphase permanenty
• During interphase, the cell experiences growth, replication of DNA, and duplication of the organelles
B. Mitosis
• Mitosis is the division of the cell’s nucleus
• It occurs in four phases:• Prophase• Metaphase• Anaphase• Telophase
1. Prophase• The chromatin changes
into a more mature form:
chromatin chromatid chromosomes
• The nuclear membrane will disappear
• The centrioles and spindle fibers will appear
2. Metaphase
• Chromosomes will line-up at the cell’s equator
(move to the middle)
3. Anaphase• The spindle fibers
pull the chromosomes apart
chromosomes chromatid
4. Telophase• The chromatid
unwind into chromatin
• The centrioles and spindle fibers disappear
• The nuclear membrane reappears
Telophase in an animal cell:
C. Cytokinesis
• Cytokinesis is the division of the cell membrane and cytoplasm
• In plant cells, a cell plate forms in between the new cells. The cell plate eventually forms a cell wall.
C. CytokinesisC. Cytokinesis
In plant cells a cell plate forms in between In plant cells a cell plate forms in between the new cells and will become the cell the new cells and will become the cell membrane. A cell wall then forms around membrane. A cell wall then forms around the cells.the cells.
III. Mistakes in Mitosis
• Cancer is a disease in which cells grow and divide uncontrollably, damaging parts of the body around them.
IV. Meiosis
• Meiosis is the formation of sex cells or gametes.
• Sex cells contain half the number of chromosomes that normal body cells have• normal cells in humans have 46• sex cells in humans have 23
• When two sex cells combine they form a zygote.
IV. Meiosis
• Meiosis is basically mitosis twice without replication after the initial mitosis.
• Meiosis has two divisions:• the first division reduces the number of
chromosomes (from 46 to 23)• the second division makes another copy of
the cell
IV. Meiosis
A. The Results of Meiosis
• In Females – one egg and three polar bodies form
• In Males – four sperm cells form
V. Genetic Inheritance
• The male sperm cell and the female egg cell join together to form a zygote
• The sperm contributes 23 chromosome and the egg contributes 23 SIMILAR chromosomes
• These similar chromosomes pair up and form homologous chromosomes
A. Karyotype
• A karyotype is a picture of one’s chromosomes
B. Homologous Chromosomes
• These chromosomes are sorted into similar pairs called homologous chromosomes
• The 23rd pair tells us if it is male or female• Male XY• Female XX
VI. Mistakes in Meiosis
• Nondisjunction is one of the most common errors that occurs in meiosis
• In nondisjunction, some chromosomes fail to split apart during anaphase
• This causes the resulting cells to have too many or too few chromosomes
VI. Mistakes in Meiosis
A. Trisomy 21
• Trisomy 21 occurs when a person has an extra 21st chromosome.
• Some characteristics include slow mental development, heart problems, small head, a distinct crease in the palm of the hand
One day old infant