Transcript Unit 2 Reproduction

4.1 The Function of the Nucleus
within the Cell
Animal Cells
Animal cells are
equipped with
many structures
that allow the cell to
perform a variety of
functions.
See page 122
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Cell Parts and Organelles
Animal Cell Parts (also found in plant cells)
cell membrane - thin covering that controls the flow of materials in and out of the cell.
cytoplasm - jelly-like substance contains the organelles (specialized cell parts)
mitochondria - provide energy for cells
ribosomes - manufacturing plants for proteins
endoplasmic reticulum - membrane-covered channels that act as a transport system
for materials made in the cell
vesicles - membrane-covered sacs formed by the endoplasmic reticulum. Vesicles
transport new proteins to the Golgi body.
Golgi body - sorts and packages proteins for transport
nucleus - controls all cell activities
nucleolus - membrane-free organelle that makes ribosomes
nuclear membrane - protects the contents of the nucleus
Nuclear pores - openings in the nuclear membrane that allow only certain materials to
pass
vacuoles - membrane-bound storage containers
See pages 122 - 124
(c) McGraw Hill Ryerson 2007
Cell Parts and Organelles
Plant Cells
Plant cells are
equipped with
some structures
that animal cells do
not have.
chloroplasts - trap energy from Sun to
make glucose, food for the plant
cell wall - tough, rigid structure that
surrounds cell membrane, provides
protection and structural support
large vacuoles - plant cells are
equipped with a large vacuole for
storing water
See pages 122 - 124
(c) McGraw Hill Ryerson 2007
The Nucleus and DNA
• The nucleus contains DNA (deoxyribonucleic acid);
DNA is the molecule has the master set of instructions for
how cells function, what they will produce, and when they will die
Structure of DNA
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DNA looks like a twisted ladder - two strands
wrap around each other in a spiral shape.
The sides of the DNA ladder are made of
sugar and phosphate.
The steps of the ladder are made of four
nitrogen bases: adenine (A), guanine (G),
cytosine (C), and thymine (T).
The bases join in a specific way
• A always joins with T
• G always joins with C
See page 126
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DNA Structure
See page 126
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DNA in the Nucleus
• Most of the time DNA is in the form of chromatin
• Chromatin coils tightly into X-shaped chromosomes
• Every organism has a specific
number of chromosomes
• Human cells have 46
chromosomes arranged in
23 pairs
• The 23rd pair determines sex;
XX for females and XY for
males
See pages 127 - 128
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Genes
• Genes are small segments of DNA
located on a chromosome
• Genes store the information needed
to produce proteins
• Each chromosome can carry
thousands of genes
• All your body cells have the same genes,
but only specific genes are “read” in
each cell to produce specific proteins
• Specialized proteins called enzymes and
hormones carry out important specific
functions in the body
See pages 129 - 130
(c) McGraw Hill Ryerson 2007
Production of Proteins
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Protein production in the cell involves several
important steps:
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The nucleus receives a chemical signal to make a specific protein.
The DNA message for the protein is copied into a small molecule called RNA.
RNA leaves the nucleus through a nuclear pore.
The RNA message is delivered to a ribosome, the ribosome makes the
protein.
The manufactured protein enters the endoplasmic reticulum (ER).
A vesicle forms at the end of the ER, and carries the protein to the Golgi body.
The Golgi body repackages the protein for transport out of the cell.
A vesicle forms off the end of the Golgi body to carry the protein to the cell
membrane.
The vesicle attaches to the cell membrane, and its protein contents are
released out of the cell.
Take the Section 4.1 Quiz
(c) McGraw Hill Ryerson 2007
See page 131
4.2 Mutation
• A gene mutation involves a change in the order of
bases (A,C,T,G) that make up the gene. There are several types of
gene mutation:
• Deletion (base missing)
• Addition (extra base added)
• Substitution (one base substituted for another)
• Gene mutations may produce proteins that are
beneficial or harmful to the organism, or may have
no effect at all.
• Example: a particular mutated gene produces
white coat Kermode bears - they occur as only
a small percentage of the population (they are
normally black in colour).
GNU License Photo
See pages 136 - 138
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Effects of Mutations
• Positive Mutations
• When a gene mutation benefits the individual.
• Example: Some plants have developed resistance to bacterial
and fungal infections.
• Negative Mutations
• When a gene mutation harms the individual
• Example: Sickle cell genes in affected humans cause blood cells
that are abnormally shaped.
• Neutral Mutation
• When a gene mutation has no effect on the individual
• Example: The white Kermode bear
See pages 139 - 140
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Mutagens & Mutation Repair
• Mutagens are substances or factors that cause mutations
• Environmental mutagens such as mercury, cigarette smoke, X-ray and
UV radiation, and certain viruses can cause mutations
• Correcting mutations is difficult, but new techniques such as gene
therapy offer hope.
• Gene therapy is complicated and experimental:
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A virus in engineered to carry a normal gene
The virus must somehow be targeted to the cells with the defective gene
The normal gene must then replace the defective gene
The normal gene must then be “switched on” so that the replacement
normal gene produces the proper healthy proteins. It is also important that
the normal gene make the correct amount of healthy protein.
Take the Section 4.2 Quiz
(c) McGraw Hill Ryerson 2007
See pages 141 - 143
5.1 The Cell Cycle and Mitosis
• Due to the loss and death of cells, the body must
replace them. A good example of this is human skin cells - each day
millions are shed.
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The life of a cell is divided
into three stages known as
the cell cycle:
Interphase: cell carries out
normal functions.
Mitosis: nucleus contents
duplicated and divide into
two equal parts.
Cytokinesis: separation of
two nuclei and cell contents
into two daughter cells.
See pages 150 - 153
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Parts of the Cell Cycle
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Interphase, the longest cell cycle stage, is when a cell
performs normal functions and grows. For example, an intestinal
lining cell absorbing nutrients.
In late interphase, DNA copies itself in the process of replication.
Replication involves several steps:
1.
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3.
The DNA molecule unwinds with the help of an enzyme.
New bases pair with the bases on the original DNA.
Two new identical DNA molecules are produced.
See pages 153 - 154
(c) McGraw Hill Ryerson 2007
Mitosis
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At the end of interphase, the cell continues to grow and
make proteins in preparation for mitosis and cytokinesis.
Mitosis
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Mitosis is the shortest stage of the
cell cycle where the nuclear contents
divide, and two daughter nuclei are
formed. It occurs in 4 stages: Prophase,
Metaphase, Anaphase and Telophase.
As the nucleus prepares to divide,
replicated DNA in interphase joins to
form sister chromatids, joined by a
centromere.
See pages 155 - 156
(c) McGraw Hill Ryerson 2007
Stages of Mitosis
Early Prophase - nucleolus disappears and spindle fibres form
Late Prophase - spindle fibres attach to centromeres of chromosomes
Metaphase - chromosomes align on equator of cell
Anaphase - spindle fibres pull sister chromatids to opposite poles of cell
Telophase - in this final stage, spindle fibres disappear and a nuclear
membrane forms around each separated set of chromosomes.
Cytokinesis is the separation of the nuclei into two daughter cells
See pages 156 - 157
(c) McGraw Hill Ryerson 2007
Cell Cycle Problems
Checkpoints in the cell cycle will prevent division if:
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If the cell is short of nutrients
If the DNA within the nucleus has not been replicated
If the DNA is damaged
Mutations in genes involving checkpoints can result in an out-of-control
cell cycle. The result can be uncontrolled cell division: cancer.
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Cancer cells have large, abnormal nuclei
Cancer cells are not specialized, so they serve no function
Cancer cells attract blood vessels and grow into tumours.
Cells from tumours can break away to other areas of the body
Take the Section 5.1 Quiz
(c) McGraw Hill Ryerson 2007
See pages 159 - 161
5.2 Asexual Reproduction
• A clone is an identical genetic copy of its parent
• Many organisms naturally form clones via asexual reproduction
• Cloning is also used in agriculture and research to copy desired
organisms, tissues and genes
Type of Asexual Reproduction
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Binary fission - single cell organisms splitting into identical copies
Budding - areas of multicellular organisms undergo repeated mitosis to form
an identical organism. Buds sometimes detach to form a separate organism
Fragmentation - part of an organism breaks off due to injury, and the part
grows into a clone of the parent
Vegetative reproduction - special cells in plants that develop into structures
that form new plants identical to the parent
Spore formation - some bacteria, micro-organisms and fungi can form
spores - single cells that can grow into a whole new organism
See pages 168 - 175
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Asexual Reproduction
Grafting
Binary
fission
Bud ----->
Budding
in Hydra
Vegetative reproduction
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Asexual Reproduction
Advantages and Disadvantages
See page 175
(c) McGraw Hill Ryerson 2007
Human Assisted Cloning
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Humans use all the asexual cloning methods in order to
produce desired results with organisms. This is done in several ways:
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Reproductive cloning - purpose is to produce a genetic duplicate of an
existing or dead organism. Steps involved:
1. Remove nucleus from an egg cell
2. A mammary gland cell is removed
from an adult female
3. Electricity fuses mammary and egg cell
4. Fused cell begins dividing
5. Dividing embryo is inserted into
surrogate mother
See pages 176 - 177
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Cloning Dolly
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Therapeutic cloning
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Human Assisted Cloning
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Therapeutic cloning - purpose is to correct health problems
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Very important to therapeutic cloning are stem cells - cells that
can become different types of cells
Stem cells can be used to replace cells
damaged from injuries or disease
Diabetes, spinal injuries, Parkinson’s
disease are only a few that can
benefit from stem cell therapy
Controversial because the best
stem cells are from embryos which
are destroyed when harvesting cells
Mouse Stem Cells
Take the Section 5.2 Quiz
(c) McGraw Hill Ryerson 2007
See pages 177 - 178
6.1 Meiosis
• Meiosis is an important aspect
of sexual reproduction
• Sexual reproduction, through
the shuffling of DNA, produces
genetic diversity.
• This variation offspring
produces individuals that
may have advantages
over one another.
See pages 188 - 189
(c) McGraw Hill Ryerson 2007
Role of Gametes
• Normal body cells have a diploid chromosome number,
meaning chromosomes occur in pairs. In humans, the male and
female each contribute 23 chromosomes - when fertilization takes
place, 23 (egg) + 23 (sperm) = 46 (zygote)
• The zygote goes on to develop into an embryo, and on into a
complete individual. When the time comes, the cycle repeats humans produce gametes (either egg or sperm) that have half
(haploid) the normal number of chromosomes.
See page 190
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Meiosis
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Meiosis produces gametes with half the chromosomes
compared to body cells:
See pages 191 - 192
(c) McGraw Hill Ryerson 2007
Meiosis Events
Meiosis I
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Matching chromosome pairs (homologous chromosomes) move to opposite
poles of the cell - two daughter cells result.
Meiosis II
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Chromatids of each chromosome are pulled apart - the end result is four
haploid cells, each with half the number of chromosomes. These develop into
gametes.
Crossing Over
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In meiosis I, chromatids of chromosome pairs can cross over each other and
exchange DNA segments - this increases genetic possibilities and produces
more variation
Independent Assortment
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The pairs of chromosomes in meiosis I separate independently, creating
many different combinations of chromosomes in the daughter cells
See pages 191 - 193
(c) McGraw Hill Ryerson 2007
Meiosis Details
Gametes do not form equally in males and females
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In males, all 4 cells resulting from meiosis develop into sperm.
In females, 1 cell gets most of the cytoplasm and becomes the egg.
Chromosome mutations sometimes occur spontaneously
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Chromosome changes during meiosis can cause changes in the genetic
information. Parts of chromosomes can be inverted, deleted, duplicated or
moved to another spot.
Cromosome mutations can occur because of mutagens
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Chromosome changes, sometimes leading to genetic disease or death, can
be cause by mutagens such as radiation or chemicals.
Failed separation of chromosomes in meiosis has serious consequences
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Failed separation means that a gamete may end up with no chromosome or
too many of a chromosome. Zygotes that result from these gametes rarely
survive, and if they do, they will have serious genetic disorders.
See pages 194 - 195
(c) McGraw Hill Ryerson 2007
Genetic Disorders
The chromosomes of an individual can be studied
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By using a karyotype, geneticists
can view an individual’s chromosomes.
Certain genetic disorders or
syndromes occur when there
are specific chromosomes extra
or missing
Down syndrome usually occurs
when there is an extra 21st
chromsome
Down syndrome karyotype
Take the Section 6.1 Quiz
(c) McGraw Hill Ryerson 2007
See pages 196 - 197
6.2 Sexual Reproduction
Sexual reproduction brings non-identical gametes together
to form a new organism - it occurs in 3 stages:
• Mating - the process by which
gametes are bought together at
same place and same time
• Fertilization - process by which
egg and sperm join to form a
new organism
• Development - the process by
which an organism develops as
an embryo
See pages 204 - 206
(c) McGraw Hill Ryerson 2007
Methods of Fertilization
External or Internal Fertilization
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In order for either of these methods to produce a successfully
developing embryo, certain conditions must be met:
1. Embryo must have enough nutrients.
2. Temperature must not be too cold or too hot.
3. There must be enough
moisture so that embryo
does not dry out.
4. Embryo must be protected
from predators and items
in environment that can
potentially harm it.
See page 207
(c) McGraw Hill Ryerson 2007
External Fertilization
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In external fertilization, sperm and egg join outside parents
Advantages
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Very little energy required to mate
Large numbers of offspring produced
Offspring can be spread widely in
the environment - less competition
between each other and parents
Disadvantages
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Many gametes will not survive
Many eggs will not be fertilized
Offspring are often not protected
by parents, so many of them die
Frog Eggs - GNU Free Doc Photo
See pages 208 - 209
(c) McGraw Hill Ryerson 2007
Internal Fertilization
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In internal fertilization, sperm and egg join inside parents,
embryo is nourished inside mother
Advantages
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Embryo protected from predators
Offspring more likely to survive,
as many species will protect their
them while they mature
Disadvantages
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Much more energy required to find mate
Fewer zygotes produced, resulting in
less offspring
More energy required to raise and care
for offspring
See pages 210 - 211
(c) McGraw Hill Ryerson 2007
Pollination
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Most plants transfer male gametes as pollen. Pollen can
be carried by wind or other organisms.
See pages 212 - 214
(c) McGraw Hill Ryerson 2007
Embryonic Development
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Embryonic development is the early development of an
organism - in humans, it is the first two months after fertilization
Stages
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End of the first week - ball of cells
called morula
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By end of second week it is a
hollow ball called a blastula
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Cells at this stage are stem cells,
and have the ability to develop
into any kind of cell
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In the next stage the embryo is
known as a gastrula and develops 3
layers: ectoderm (skin, nerves),
mesoderm (muscles, bones), and
endoderm (lungs, liver, digestive
system lining)
See pages 216 - 217
(c) McGraw Hill Ryerson 2007
Fetal Development
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The cell layers now differentiate into the organs and
tissues of a baby - this is divided into 3 trimesters.
First Trimester (0-12 weeks)
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Organ systems begin to develop
and form. Bone cells form.
Second Trimester (12-24 weeks)
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Rapid growth from 12-16 weeks.
Third Trimester (24+ weeks)
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Continued growth, especially of brain. Fat begins
to deposit at 32 weeks to keep baby warm at birth.
See pages 218 - 219
(c) McGraw Hill Ryerson 2007
Sexual Reproduction
Advantages and Disadvantages
Take the Section 6.2 Quiz
(c) McGraw Hill Ryerson 2007
See page 220
6.3 Assisted Reproductive
Technologies
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Infertility is the inability of a couple to have a baby
Assisted reproductive technologies involve removing eggs from the
woman, fertilizing them, and returning them to the uterus.
Types of Assisted Reproductive Technologies
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Artificial Insemination - donor sperm is placed in the female.
In vitro fertilization (IVF) - egg and sperm are collected and fertilization takes
place in a dish. Embryo(s) then placed in female’s uterus.
Gamete intrafallopian transfer (GIFT) - eggs and sperm are collected, mixed,
then injected into the woman’s fallopian tubes.
Intracytoplasmic Sperm Injection (ICSI) - a single sperm is injected directly
into an egg.
Reproductive technologies help childless couples, but carry a higher
risk of birth defects. Also creates the problem of “unwanted” embryos.
What should be done with them?
Take the Section 6.3 Quiz
(c) McGraw Hill Ryerson 2007
See pages 224 - 229