Chapter 6 Chromosomes and Cell Reproduction

1
Chapter 6 Chromosomes and Cell Reproduction
2
New Cells are Formed by Cell Division

• - an adult human body produces about 2 trillion
  cells EVERY day! This is about 25 million new
  cells per second!
• - Cell division (or cell reproduction) allows for
  this.
• - cell division can differ depending on the
  organism and why the cell is dividing

3
Bacterial Cells

•  - Bacteria reproduce by a type of cell division
  called Binary Fission.
•  - Binary fission is a form of asexual
  reproduction that produces identical offspring.
•  - In asexual reproduction a single parent passes
  exact copies of its entire DNA to its offspring.

4

• Eukaryotic organisms undergoing growth,
  development, repair, or asexual reproduction
  divide by a different type of cell division
  (mitosis)
• And finally, the formation of Gametes or
  reproductive cells (egg and sperm) undergo a
  third type called Meiosis

5
Eukaryotic cells form chromosomes before cell
division

• - a gene is a segment of DNA that codes for a
  protein or RNA molecule.
• - as a Eukaryotic cell prepares to divide, the
  DNA is copied into two exact strands called
  chromatids.

6

• - the Chromatids coil into structures called
  Chromosomes that are attached at a point called a
  Centromere (p. 119)
• - during cell division the chromatids become
  separated and placed in each new cell which
  ensures each one will have identical genetic
  information as the original

7
Centromere
8
Chromosome number and structure affect
development.

• - Each human somatic (any cell besides sex cells)
  normally contain two copies of 23 chromosomes for
  a total of 46 chromosomes.
•   - Each chromosome contains thousands of genes
  that play important roles in determining how a
  persons body develops and functions.

9

• - Each of the 23 pairs of chromosomes consists of
  two homologous chromosomes.
• - Homologous chromosomes are chromosomes that are
  similar in size, shape and genetic content.

10

• - All of the cells in the body, besides gametes
  have two pairs of chromosomes. (one from mom, one
  from dad) they are called Diploid.
• - Sex cells only have a pair, they are called
  Haploid (1/2 the amount of chromosomes)
• - Two Haploid gametes fuse (fertilization)
  to form a zygote (the first cell of a new
  individual).

11
Chromosomes
- and check out p. 121 for the number of
chromosomes in other organisms
12
Chromosomes determine your sex.

• - of the 23 pairs of chromosomes in human somatic
  cells, 22 pairs are called autosomes
•   - Autosomes are chromosomes that are not
  directly involved in determining the sex of an
  individual.
•  - The sex chromosomes, one of the 23 pairs
  contain the gene that determines the gender.
  Males determine the gender of the human.

13
Change in chromosome number

• - Humans must have all 46 chromosomes to survive
• - However, a human can survive with more than two
  copies of a chromosome, a condition called
  Trisomy
•   - Individuals with Down Syndrome have an extra
  copy of chromosome 21
•  

14
The Cell Cycle

• - The cell cycle describes the life of a
  Eukaryotic cell.
• - The cell cycle is a repeating sequence of
  cellular growth and division during the life of
  an organism.
• - A cell spends 90 of its time in the first
  three phases of the cycle called Interphase.
•  

15
Interphase(p.125)

• 1. First growth (G1) phase a cell grows rapidly
  and carries out its routine functions. Cells
  that are not dividing remain in the G1 phase.
•   2. Synthesis (S) phase A cells DNA is copied
  during this phase. At the end of this phase,
  each chromosome consists of two chromatids
  attached at the centromere.

16

• 3. Second growth (G2) phase In the G2 phase,
  preparations are made for the nucleus to divide.
  
•   4. Mitosis the process during cell
  division in which the nucleus of a cell is
  divided into two nuclei.
• - each nucleus ends up with the
  same number and kinds of
  chromosomes as the original cell.
•  

17

• 5. Cytokinesis the cytoplasm splits.
•  

Mitosis and Cytokinesis produce new cells that
are identical to the original cells and allow
organisms to go, replace damaged tissue and in
some organisms reproduce asexually
18
The cell cycle is carefully controlled
- cells have a system that controls the phases
of the cell cycle
- feedback signals from the cell either trigger
or block the next phase
- controlled by numerous proteins
19
When control is lost Cancer
Certain genes contain the information necessary
to make the proteins that regulate cell growth
and division.
If one of these genes is mutated, the protein may
not function and cells may grow uncontrolled or
stop the cell cycle (sometimes environmental or
lifestyle)
20
Mitosis

• I Prefer Mangos And Tangerines
• Interphase (not really a mitosis phase)
• Prophase
• Metaphase
• Anaphase
• Telophase

21
PROPHASE

• - this is the longest phase and during this
  phase
• The nuclear envelope disappears.
• The centrioles start to move to the opposite
  poles.
• Spindle fibers start to form.
• Chromosomes are becoming evident.

22
PROPHASE
23
METAPHASE

• is the shortest phase of mitosis.
• chromosomes move to the center of the cell and
  line up along the equator
• Spindle fibers link the chromosomes to opposite
  poles

24
METAPHASE
25
ANAPHASE

• Begins when the centromere that joins the sister
  chromatids start to split.
• The chromosomes are being pulled to the opposite
  sides of the cell toward the poles.

26
ANAPHASE
27
TELOPHASE

• Final process of mitosis.
• Chromosomes are at the opposite poles.
• Nuclear envelope reforms.

28
TELOPHASE
29
CYTOKINESIS splitting of the cytoplasm
30
Mitosis ensures that both nuclei have exactly
equal genetic information, but cytokinesis
distributes the organelles (mitochondria,
ribosomes, etc.) and cytoplasm randomly. That's
OK as long as enough organelles are present so
the cell will be viable.