Transcript Chromosomes and Cell Reproduction

CHROMOSOMES
AND CELL
REPRODUCTION
Section I Chromosomes
Formation of New Cells by
Cell Division
• New cells are formed when old cells
divide.
• 1. Cell division is the same as cell
reproduction.
• 2. The type of cell
division
differs
.
depending on the organism.
Prokaryotic cells, like Bacteria
reproduce by binary fission.
• Binary fission: asexual/ a single parent
passes exact copies of its DNA to its
offspring
• 1st stage: DNA is copied
• 2nd stage: Cell divides
Eukaryotic cells reproduce by another type
of cell division-
MITOSIS
• 1st stage: DNA is copied
• chromatids: 2 exact copies of DNA that make
up a chromosome
• centromere: point of attachment
of 2 chromatids
• 2nd Stage: DNA and protein coil into
chromosomes
• Draw and Label a chromosome:
• The chromatids separate during cell
division and are each placed into a new
cell. This ensures that each cell has the
same genetic information as the original
cell.
• When a cell divides: the DNA is copied 1st
and then distributed. Each cell ends up
with a complete set of the DNA.
Gamete cells- which are sperm and
egg are created through another type
of cell division-MEIOSIS
Egg cell surrounded by
sperm cells.
II. Chromosome Number and
Structure
• Humans have 46 chromosomes
(23 Pairs) in somatic cells.
• Somatic cells: All body cells
(except sex cells)
• Gametes: sex cells (sperm and
eggs)
• Chromosomes differ in size,
shape and set of genes.
Sets of Chromosomes
• Homologous chromosomes are
those that are paired together and
are similar in size, shape and
genetic content.
• 46 chromosomes = 2 sets of 23
Diploid- cell contains 2 sets of chromosomes
Haploid- cell contains 1 set of chromosomes
The fusion of 2 haploid cells forms a diploid
zygote.
Zygote-fertilized egg cell
B. Sex Chromosomes
• Out of 23 pairs of chromosomes- 22
pairs are autosomes; 1 pair are sex
chromosomes.
• Sex chromosomes are the X and Y.
• Male Sperm determines the sex of a
child.
• XX = Female
XY = Male
C. Change in Chromosome Number
• There are 1000’s of genes on each of our
chromosomes.
• The presence of all 46 chromosomes is
essential for normal development and
function.
• Trisomy- having an extra copy of a
chromosome
• Example: Trisomy 21- Down’s Syndrome
• Cause of Trisomy is NONDISJUNCTION.
• This is when the chromosomes don’t separate
and one gamete ends up with 2 chromosomes.
Mikey has Down’s Syndrome.
He has an extra chromosome. Instead of having a
pair of # 21 chromosomes, he as 3 copies of it.
Karyotype:
Normal vs Down’s Syndrome
D. Change in Chromosome
Structure- MUTATIONS
• Types of Mutations:
1. Deletion- piece of chromosome breaks off
2. Duplication- extra chromosome fragment
attaches; 2 copies of certain genes
3. Inversion- chromosome attaches in
reverse order
4. Translocation – chromosome piece
attaches to a nonhomologous chromosome
Draw these Chromosomal Mutations
Jacobsen syndrome: report of a patient with
severe eye anomalies, growth hormone
deficiency, and hypothyroidism associated
with deletion 11
Section II- The Cell Cycle
A. Cell cycle-Cellular growth and division
• 90% of the time is spent in Interphase.
(preparation to divide)
• The cell will enter the last 2 phases of
the cell cycle only if it is about to divide.
5 Phases of the Cell Cycle
The 1st 3 stages are part of Interphase.
• 1. 1st Growth (G1)-Grows rapidly (nerve
cells stay in this stage)
• 2. Synthesis- DNA is copied; each
chromosome is copied
• 3. 2nd Growth (G2)- Growth; prep for
division; microtubules are assembled
• 4. Mitosis- nucleus divides into 2 nuclei
(2 cells) that are identical
• 5. Cytokinesis- cytoplasm divides
• Mitosis and cytokinesis
produce new cells that are
identical to the original cells
and allow organisms to grow,
replace damaged tissue, and
in some organisms,
reproduce.
B. How do cells “know” when to divide?
“Red light- Green light”
• The cell cycle in eukaryotes is controlled by
many proteins.
• 1.Cell growth check point(G1): makes
decision whether cell will divide
• 2. DNA synthesis checkpoint (G2):
protein triggers mitosis and cell begins
many processes needed to proceed into
mitosis
• 3. Mitosis checkpoint: triggers the exit from
mitosis; It signals the beginning of G1.
G1 Checkpoint –
proteins make sure
enough growth has
occurred
Synthesis Phase
“S” phase
-
Growth Phase 1
First Growth Phase
G1
- Grows, grows
Duplication, Replication,
“copying” chromosomes
Mitosis
Dividing of
the nucleus –
2 cells
Mitosis
Checkpoint – proteins
check to make sure
divisions has completed.
Growth Phase 2
Second Growth Phase
G2
- Grows, centrioles double,
start moving to opposite
poles, microtubules form
G2 Checkpoint –
proteins make sure
enough growth has
occurred and
chromosomes have
replicated completely
CANCER• Uncontrolled growth of cells
• It is essentially a disorder of cell division.
• Cancer cells do not respond normally to the
body’s control mechanisms
• Some Mutations cause cancer by over-producing
growth-promoting molecules, thus speeding up
the cell cycle or by inactivating the control
proteins that normally act to slow or stop the
cell cycle.
Section III Mitosis and
Cytokinesis
• 4 stages of Mitosis:
1. Prophase
2.Metaphase
3. Anaphase
4. Telophase
Prophase:
• Chromosomes become visible, the
nuclear envelope dissolves and the
spindle forms.
• What makes up the spindles? It is made
up of centrioles & individual
microtubule fibers; they are involved in
moving the chromosomes.
Metaphase
• Chromosomes line up in the Middle
(middle phase)
Anaphase
• Centromeres divide, chromatids move
toward opposite poles.
Telophase
• Nuclear envelope reforms at each pole,
chromosomes uncoil , spindle divides.
• Mitosis is complete and cytokinesis begins.
Cytokinesis
• Cytoplasm divides in half, and the
membrane grows to enclose each cell, 2
separate cells are formed.
A Difference in Plant Cells
• A cell plate forms across the middle
of the plant cell. A new cell wall
forms on both sides of the cell
plate.
Put the following in the correct
order
• Put the following pictures in the correct order as
they occur during mitosis:
• Answer: c,b,d,a