Download Ch 6. Chromosomes and Cell Reproduction

Ch 6. Chromosomes and
Cell Reproduction
Where it all began…
You started as a cell smaller than
a period at the end of a sentence…
And now look at you…
How did you
get from there
to here?
Getting from there to here…

Going from egg to baby….
the original fertilized egg has to divide…
and divide…
and divide…
and divide…
Enduring Understanding
Biological systems utilize free energy &
molecular building blocks to grow, reproduce,
& maintain dynamic homeostasis.
Essential Questions
How do organisms grow bigger after
they are born?
How do cells know when to divide?
What is cancer?
6.1: Chromosomes
About 2 trillion cells are produced by an adult
human body every day!
- about 25 million new cells per second!
Type of cell division differs depending on:
- the organism
- why the cell is dividing
WHY Cells Divide:
1.
growth & repair
2.
creation of gametes (sex cells)
3.
method of reproduction in
unicellular organisms

Regardless of the type of cell division that
occurs, all of the information stored in the
molecule DNA must be present in each of the
resulting cells.

When a cell divides, DNA is first copied & then
distributed.

Each cell ends up with a complete set (copy) of
the DNA.
Prokaryotic Cell Division

Binary Fission
- type of reproduction that occurs in
bacteria
- single celled organism splits & becomes
two identical organisms

3 stages
STAGE 1 - Chromosome,
which is attached to the
inside of membrane,
makes a COPY of itself
STAGE 2 - Cell grows till
about TWICE Normal
Size. CELL WALL forms
between the two
Chromosomes.
STAGE 3 - Cell SPLITS
into 2 NEW CELLS.
2 identical haploid cells
Binary fission - 2:22
Chromosomes and DNA
Chromosomes are DNA wrapped around
proteins to form an X-shaped structure.
1. Chromosomes are
found in the
nucleus
2. Chromosomes are
made of DNA
3. Sections of
chromosomes are
called genes
DNA - deoxyribonucleic acid (it is the genetic code that contains all the
information needed to build and maintain an organism)
Journey into DNA
Chromosome Numbers

Each organism has a distinct number of
chromosomes

Humans, 46 chromosomes =
2 copies of 23 chromosomes
2 copies of 23 TYPES of
chromosomes

Other organisms have different numbers
 EX:
Dog 78 chromosomes
Diploid numbers of some commonly studied organisms
(as well as a few extreme examples)
Homo sapiens (human)
46
Mus musculus (house mouse)
40
Drosophila melanogaster (fruit fly)
8
Caenorhabditis elegans (microscopic roundworm)
12
Saccharomyces cerevisiae (budding yeast)
32
Arabidopsis thaliana (plant in the mustard family)
10
Xenopus laevis (South African clawed frog)
36
Canis familiaris (domestic dog)
78
Gallus gallus (chicken)
78
Zea mays (corn or maize)
20
Muntiacus reevesi (the Chinese muntjac, a deer)
23
Muntiacus muntjac (its Indian cousin)
6
Myrmecia pilosula (an ant)
2
Parascaris equorum var. univalens (parasitic roundworm) 2
Cambarus clarkii (a crayfish)
200
Equisetum arvense (field horsetail, a plant)
216
Chromosome Numbers

Somatic Cells - body cells, such as muscle, skin,
blood ...etc.

Contain a complete set of chromosomes & are called
DIPLOID.
 DIPLOID
= 2 SETS OF 23 CHROMOSOMES
2 copies of 23 TYPES of
chromosomes
23 pairs of homologues
2n
Diploid –23 pairs (or 2 sets of 23)

Sex Cells - also known as gametes.

Contain half the number of chromosomes as body
cells and are called HAPLOID
 HAPLOID – 1 SET OF 23 CHROMOSOMES
1 set of 23 TYPES of
chromosomes

n
Haploid – 1 set only
Sets of chromosomes
Homologous Pairs (or homologues).

Similar in size, shape, and genetic content

Each homolog comes from one parent

Imagine as a matching set, but they are not
exactly alike, like a pair of shoes.
Sets of chromosomes
Diploid cells
23 homologous pairs = total of 46
 2 sets of chromosomes
 2n

Haploid cells
23 chromosomes (that are not paired) = total
of 23
 One set of chromosomes
n

Homologous
Chromosomes
BOTH CHROMOSOMES IN A
HOMOLOGOUS PAIR CONTAIN
INFORMATION THAT CODE THE
SAME TRAIT (GENES).
Example Eye Color.
Why have homologues?

The chromosomes of many organisms come in
pairs – WHY?

Mutations are common.

Cells with two copies of each gene are more
likely to survive a mutation in one of them, b/c
the remaining gene can still produce a normally
functioning protein.

Not all cells have pairs of homologues – sex
cells do not.
Creation of a Zygote

2 sex cells, or
gametes come
together, the
resulting fertilized
egg is called a
ZYGOTE

Zygotes are diploid
and have the total
46 chromosomes
(in humans)
Sex Chromosomes
 Autosomes
not directly involved in
determining the sex (gender) of an
individual.
 in
humans 22 pairs
 All other genetic info
 Sex
chromosomes determines the
sex on the individual.

one pair
Sex Chromosomes
In humans and many other organisms,
referred to as X & Y


Male Y

Female X

Male can donate X or Y
Female can donate X or X

Y
X
XX and XY karyotype
Sex chromosomes

Structure & number vary

EX: Grasshoppers – no Y chromosome


Female is XX
Male is XO


O indicates the absence of a chromosome
EX: Birds, moths, & butterflies – male has two X
and female has only one X
Change in chromosome number

Each of an individual’s 46 chromosomes has
thousands of genes.

ALL important for normal development.

Trisomy – human with more than two copies of
a chromosome


Will not develop correctly
Down syndrome – have 3 copies of chromosome 21

Karyotype –a photo of the chromosomes in a
dividing cell that shows the chromosomes
arranged by size.
Standard Human Karyotype
Down syndrome
Trisomy – human with more than two copies of a chromosome
Nondisjunction
MUTATIONS– Change in chromosome structure
1.
Deletion mutation –a piece of a chromosome
breaks off completely
2.
Duplication mutation- 2 copies of a certain set
of genes
3.
Inversion – chromosome reattaches but in
reverse orientation
4.
Translocation –piece reattaches but in different
spot
What type of mutation is it???
Genes are permanently lost as they become
unattached to the centromere
Deletion
•Information from one of two homologous
chromosomes breaks and binds to the other.
- Usually this sort of mutation is
LETHAL!
Translocation
- Mutants genes are displayed twice
- Can be advantageous as no genetic information
is lost or altered and new genes are gained
Duplication
-Connections break & sequence reversed
- New sequence may not be viable to produce an
organism, depending on which genes are reversed.
- Advantageous characteristics also possible
Inversion
Mini quiz
Prokaryotes reproduce asexually by
A. Disjunction
B. Binary fission
C. Cytokinesis
D. Mitosis
Put the following steps in order
4 New cell wall forms around the new membrane.
_____
2 New cell membrane is added to a point on the
_____
membrane between the two DNA copies.
5
_____
The bacterium is pinched into two independent cells.
3
_____ The growing cell membrane pushes inward, and the
cell is constricted in two.
1
_____ DNA is copied.
Chromosomes that are similar in size,
shape, and genetic content are called
_______________.
homologous
A cell, such as a somatic cell, that contains
two sets of chromosomes is said to be
diploid
________________.
n
Biologists use the symbol ______to
represent one set of chromosomes.
A fertilized egg cell, the first cell of a new
zygote
individual, is called a(n) __________.
What is the difference between an autosome
and a sex chromosome?
Autosome = do not determine sex = all
others
Sex chromosome = determine sex
What is a karyotype?
Photograph of the chromosomes in a
dividing cell that shows the chromosomes
arranged by size.
T or F
1.
At cell division, each chromosome
consists of two chromatids attached at a
centromere.
T
2.
The normal diploid number for humans is
23. F
3.
A person with the sex chromosomes XX
would be a female.
T
6.2: The Cell Cycle
The Cell Cycle

Cell division in eukaryotes is more
complex than cell division in bacteria b/c it
involves dividing cytoplasm &
chromosomes inside the nucleus.

The life of a eukaryote cell is typically
shown as a cell cycle.
THE PHASES OF LIFE OF A CELL
ARE CALLED THE CELL CYCLE
3 PHASES:
A. INTERPHASE
– first growth phase
 S phase – synthesis phase
 G2 phase – second growth phase
 G1
B. MITOSIS
C. CYTOKINESIS.

CELL CYCLE -Repeating events that
make up the life of a cell.
Know
function of
each
phase
Note G0
G0 – said to be
quiescent
•May re-enter
the cell cycle
later, may not
divide, may die

Mitosis (division of the nucleus) &
cytokinesis (splitting of the cell) produce new
cells that are identical to the original cells &
allow organisms to:
 grow
 replace damaged cells
 reproduce asexually (in SOME organisms)
Control of the cell cycle

If a cell spends 90% of its time in
interphase, how does it “KNOW” when to
divide?

Cells have checkpoints
(red light/ green light)

Checkpoints are controlled by
many PROTEINS
Controls at 3 main checkpoints
G1 – Cell growth checkpoint
1.


Makes the decision of whether the cell will divide
If healthy & large, proteins will stimulate cell to begin the S
phase and copy DNA
G2 – DNA synthesis checkpoint
2.


DNA replication is checked at this point by DNA repair
enzymes
If this checkpoint is passed, proteins help to trigger mitosis
Mitosis checkpoint
3.


Triggers the exit from mitosis
Signals the beginning of G1 growth phase
See picture in your textbook!
Cells alive
animation
Cell control lost = CANCER

Cancer is uncontrolled growth of cells.

Can occur when a gene that codes for proteins
that regulate cell growth & division mutates.

Cancer cells do not respond normally to the
body’s control mechanisms.

Some mutations cause cancer by speeding up
the cell cycle, & others by inactivating the control
proteins.
CANCER

Group of more than 100 diseases that
develop over time & involve the
uncontrolled division of the body’s cells.

Cancer cells are genetically unstable

prone to rearrangements, duplications, &
deletions of their chromosomes that cause
their progeny to display unusual traits.
Stand up to cancer – PSA - odds
Stand Up to Cancer Intro – 5 min
The stages of tumor development.
Malignant tumor develops across time, as a result of
mutations - the number of mutations involved in other
types of tumors can vary.
We do not know the exact number of mutations required for
a normal cell to become a fully malignant cell, but the
number is probably less than ten.
http://science.education.nih.gov/supplements/nih1/cancer/guide/understanding1.htm
The Biology of Cancer - 11 min
How cancer grows - animation
How cancer spreads video
Development of Cancer
Cancer develops only after a cell experiences ~6 key
mutations (“hits”) – exact number of mutations not
known – some say over 10 mutations to same cell
 unlimited growth


ignore checkpoints


turn ON chromosome maintenance genes
promotes blood vessel growth


turn OFF suicide genes
immortality = unlimited divisions


turn OFF tumor suppressor genes (p53)
escape apoptosis


turn ON growth promoter genes
turn ON blood vessel growth genes
overcome anchor & density dependence

turn OFF touch-sensor gene
It’s like an
out of control
car!
What causes these “hits”?

Mutations in cells can be triggered by




UV radiation
chemical exposure
radiation exposure
heat




cigarette smoke
pollution
Others?
age
Genetics
Tumors - Mass of abnormal cells

Benign tumor = does NOT spread

abnormal cells remain at original site as a lump



p53 has halted cell divisions
most do not cause serious problems &
can be removed by surgery
Malignant tumors = SPREAD

cells leave original site




lose attachment to nearby cells
carried by blood & lymph system to other tissues
start more tumors = metastasis
impair functions of organs throughout body
Traditional treatments for cancers

Treatments target rapidly dividing cells

high-energy RADIATION


kills rapidly dividing cells
Common chemotherapy side
effect is hair loss b/c drugs
attack rapidly growing cells in
your body — including those
in your hair roots.
CHEMOTHERAPY – chemical therapy (IV, injection, or pill)



stop DNA replication
stop mitosis & cytokinesis
stop blood vessel growth
New “miracle drugs”

Drugs targeting proteins (enzymes) found
only in cancer cells

Gleevec
 treatment
for adult leukemia (CML)
& stomach cancer (GIST)
 1st successful drug targeting only cancer cells
without
Gleevec
Novartes
with
Gleevec
Host of therapies
Fighting Cancer
Read Exploring Further:
Cancer p. 127

Discussion

Where in the cell cycle would scientists target
anticancer drugs?

What type of environmental factors have been
associated with the onset of cancer?
Checkpoints, DNA replication, or cytokinesis
• Diet, UV radiation, hormones, environmental pollution
•
Mini quiz
Define cell cycle.
A repeating sequence of cell growth &
division in the life of an organism.
Define mitosis.
The division of the NUCLEUS into two nuclei.
In which phase of the cell cycle is DNA
copied
A.
B.
C.
D.
G1
S
G2
Mitosis
A typical eukaryotic cell spends 90% of tis
time in _______.
A.
B.
C.
D.
Mitosis
Interphase
Anaphase
Cytokinesis
In the cell cycle of typical cancer cells,
mutations have caused
A.
B.
C.
D.
Slower growth
A failure in mitosis
Uncontrolled growth
A halt in cell division

If you were stricken with a severe form of
cancer, do you know enough to make
educated choices about your treatment?
•
No one is immune to cancer.
•
Treatment options are available, but it’s important to
understand the implications of each option.

Some forms of cancer are linked to diet, smoking, &
other avoidable conditions. What responsibility does the
government have to prevent such cancers?
•
Some people knowingly accept a higher risk of cancer by
the choices they make.
•
$ spent researching & treating avoidable cancers is not
available to help in other areas of society.
•
Government’s role is complex. Personal freedom is in
direct conflict with social & familiar responsibilities.
6.3: Mitosis and Cytokinesis

Every second about 2 million new red blood
cells are produced in your body by cell
divisions occurring in the bone marrow.
Human red
blood cells
CELL DIVISION INVOLVES 2 STEPS:
CALLED MITOTIC CELL DIVISION.
1.
MITOSIS - NUCLEUS DIVIDES INTO
TWO NUCLEI W/ IDENTICAL GENETIC
MATERIAL.
2.
CYTOKINESIS - CYTOPLASM
DIVIDES INTO TWO NEW CELLS
CALLED DAUGHTER CELLS.

During mitosis, the
chromatids on each
chromosome are
physically moved to
the opposite side of
the dividing cell with
the help of the
spindle.

Spindles- made up of
centrioles & microtubule
fibers that move
chromosomes during
cell division.

At each pole is a
centrosome –an
organelle that organizes
the assembly of the
spindle. (Centrioles in
centrosome).
P.128 picture
Read p. 129 on chromatid movement

Know graphics on p. 130-131 all steps & phases!!!
Mitosis
video
Know BOOK diagram of
STAGES OF MITOSIS
cell division - animation
Cytokinesis in Animal Cells

As mitosis ends, cytokinesis
begins.

Cytoplasm is divided in half,
& cell membrane grows to
enclose each cell.

In animal cells, the cell is
pinched in half by a belt of
protein threads.
Cytokinesis in Plant Cells

In plant cells & other cells that have rigid cell
walls, cytoplasm is divided in a different way.

Vesicles, formed by Golgi apparatus, fuse at
the middle & form a CELL PLATE.

A new cell wall will form at either side of this
cell plate.
Cytokinesis in Plant Cells
Remember….

For both animal & plant cells offspring are:


Equal in size
Has an identical copy of the
original cells’ chromosomes
Talk about Meiosis
In next chapter!
Mini quiz
Chromatids are
A.
B.
C.
D.
Dense patches within the nucleus
Prokaryotic chromosomes
Two exact copies of DNA that make up
each chromosome
Structures that move chromosomes
during mitosis
As a result of mitosis each resulting cell
A.
Receives an exact copy of all the chrom
present in the original cell
B.
Receives most of all the chrom present in the
original cell
C.
Donates a chrom to the original cell
D.
Receives exactly half the chrom from the
original cell
How does cell division differ between plant &
animal cells
A.
B.
C.
D.
Plant cells do not have centrioles
Animal cells form a cell plate
Plant cells are always haploid
Animal cells do not have centrioles
Name that phase
Metaphase
Name that phase
Prophase
Name that phase
Telephase
Name that phase
Anaphase
Name that phase
Interphase