(c) McGraw Hill Ryerson 2007 4.1 The Function of the Nucleus within the Cell Animal Cells See page...

(c) McGraw Hill Ryerson 2007

4.1 The Function of the Nucleus within the Cell

Animal Cells

See page 122

Animal cells are equipped with many structures that allow the cell to perform a variety of functions.


Cell Parts and Organelles

Animal Cell Parts (also found in plant cells)

See pages 122 - 124

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


Cell Parts and Organelles

Plant Cells

See pages 122 - 124

Plant cells are equipped with some structures that animal cells do not have.

chloroplasts - trap energy from Sun to make glucose, food for the plantcell wall - tough, rigid structure that surrounds cell membrane, provides protection and structural supportlarge vacuoles - plant cells are equipped with a large vacuole for storing water


The Nucleus and DNA

• The nucleus contains DNA (deoxyribonucleic acid);DNA is the molecule has the master set of instructions forhow cells function, what they will produce, and when they will die

Structure of DNA• 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


DNA Structure

See page 126


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 in23 pairs

• The 23rd pair determines sex;XX for females and XY formales

See pages 127 - 128


Genes

• Genes are small segments of DNAlocated on a chromosome

• Genes store the information neededto produce proteins

• Each chromosome can carrythousands of genes

• All your body cells have the same genes,but only specific genes are “read” ineach cell to produce specific proteins

• Specialized proteins called enzymes andhormones carry out important specificfunctions in the body

See pages 129 - 130


Production of Proteins

• Protein production in the cell involves severalimportant steps:

1. The nucleus receives a chemical signal to make a specific protein.

2. The DNA message for the protein is copied into a small molecule called RNA.

3. RNA leaves the nucleus through a nuclear pore.

4. The RNA message is delivered to a ribosome, the ribosome makes the protein.

5. The manufactured protein enters the endoplasmic reticulum (ER).

6. A vesicle forms at the end of the ER, and carries the protein to the Golgi body.

7. The Golgi body repackages the protein for transport out of the cell.

8. A vesicle forms off the end of the Golgi body to carry the protein to the cell membrane.

9. The vesicle attaches to the cell membrane, and its protein contents are released out of the cell.

See page 131Take the Section 4.1 Quiz


4.2 Mutation

• A gene mutation involves a change in the order ofbases (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 arebeneficial or harmful to the organism, or may haveno effect at all.

• Example: a particular mutated gene produceswhite coat Kermode bears - they occur as onlya small percentage of the population (they arenormally black in colour).

See pages 136 - 138

GNU License Photo


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


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:

• 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.

See pages 141 - 143 Take the Section 4.2 Quiz


5.1 The Cell Cycle and Mitosis

• Due to the loss and death of cells, the body mustreplace them. A good example of this is human skin cells - each day millions are shed.

• The life of a cell is dividedinto three stages known asthe cell cycle:

• Interphase: cell carries outnormal functions.

• Mitosis: nucleus contentsduplicated and divide intotwo equal parts.

• Cytokinesis: separation oftwo nuclei and cell contentsinto two daughter cells.

See pages 150 - 153


Parts of the Cell Cycle

• Interphase, the longest cell cycle stage, is when a cellperforms 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. The DNA molecule unwinds with the help of an enzyme.

2. New bases pair with the bases on the original DNA.

3. Two new identical DNA molecules are produced.

See pages 153 - 154


Mitosis

• At the end of interphase, the cell continues to grow andmake proteins in preparation for mitosis and cytokinesis.

Mitosis• Mitosis is the shortest stage of the

cell cycle where the nuclear contentsdivide, 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 toform sister chromatids, joined by acentromere.

See pages 155 - 156


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.

See pages 156 - 157 Cytokinesis is the separation of the nuclei into two daughter cells


Cell Cycle Problems

Checkpoints in the cell cycle will prevent division if:• 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.

• 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



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 genesType of Asexual Reproduction• 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


Asexual Reproduction

Bud ----->

Vegetative reproduction

Grafting

Binary fission

Budding in Hydra


Asexual Reproduction

Advantages and Disadvantages

See page 175


Human Assisted Cloning

• Humans use all the asexual cloning methods in order toproduce desired results with organisms. This is done in several ways:

• 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 removedfrom an adult female

3. Electricity fuses mammary and egg cell

4. Fused cell begins dividing

5. Dividing embryo is inserted intosurrogate mother

See pages 176 - 177


Cloning Dolly


Therapeutic cloning


Human Assisted Cloning

• Therapeutic cloning - purpose is to correct health problems

• Very important to therapeutic cloning are stem cells - cells that can become different types of cells

• Stem cells can be used to replace cellsdamaged from injuries or disease

• Diabetes, spinal injuries, Parkinson’sdisease are only a few that canbenefit from stem cell therapy

• Controversial because the beststem cells are from embryos whichare destroyed when harvesting cells

See pages 177 - 178

Mouse Stem Cells

Take the Section 5.2 Quiz


6.1 Meiosis

• Meiosis is an important aspectof sexual reproduction

• Sexual reproduction, throughthe shuffling of DNA, producesgenetic diversity.

• This variation offspringproduces individuals thatmay have advantagesover one another.

See pages 188 - 189


Role of Gametes

See page 190

• 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.


Meiosis

• Meiosis produces gametes with half the chromosomescompared to body cells:

See pages 191 - 192


Meiosis Events

Meiosis I• Matching chromosome pairs (homologous chromosomes) move to opposite

poles of the cell - two daughter cells result.

Meiosis II• 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• 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• The pairs of chromosomes in meiosis I separate independently, creating

many different combinations of chromosomes in the daughter cells

See pages 191 - 193


Meiosis Details

Gametes do not form equally in males and females• 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• 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• 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• 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


Genetic Disorders

The chromosomes of an individual can be studied

• By using a karyotype, geneticists can view an individual’s chromosomes.

• Certain genetic disorders orsyndromes occur when thereare specific chromosomes extraor missing

• Down syndrome usually occurswhen there is an extra 21stchromsome


Down syndrome karyotype


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 whichgametes are bought together atsame place and same time

• Fertilization - process by whichegg and sperm join to form anew organism

• Development - the process bywhich an organism develops asan embryo

See pages 204 - 206


Methods of Fertilization

See page 207

External or Internal Fertilization• 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 enoughmoisture so that embryodoes not dry out.

4. Embryo must be protectedfrom predators and itemsin environment that canpotentially harm it.


External Fertilization

• In external fertilization, sperm and egg join outside parents

Advantages• Very little energy required to mate• Large numbers of offspring produced• Offspring can be spread widely in

the environment - less competitionbetween each other and parents

Disadvantages• Many gametes will not survive• Many eggs will not be fertilized• Offspring are often not protected

by parents, so many of them die

See pages 208 - 209

Frog Eggs - GNU Free Doc Photo


Internal Fertilization

• In internal fertilization, sperm and egg join inside parents,embryo is nourished inside mother

Advantages• Embryo protected from predators• Offspring more likely to survive,

as many species will protect theirthem while they mature

Disadvantages• 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


Pollination

• Most plants transfer male gametes as pollen. Pollen can be carried by wind or other organisms.

See pages 212 - 214


Embryonic Development

• Embryonic development is the early development of anorganism - in humans, it is the first two months after fertilization

Stages• End of the first week - ball of cells

called morula• By end of second week it is a

hollow ball called a blastula• Cells at this stage are stem cells,

and have the ability to developinto any kind of cell

• In the next stage the embryo isknown as a gastrula and develops 3layers: ectoderm (skin, nerves),mesoderm (muscles, bones), andendoderm (lungs, liver, digestivesystem lining)

See pages 216 - 217


Fetal Development

• The cell layers now differentiate into the organs andtissues of a baby - this is divided into 3 trimesters.

First Trimester (0-12 weeks)• Organ systems begin to develop

and form. Bone cells form.

Second Trimester (12-24 weeks)• Rapid growth from 12-16 weeks.

Third Trimester (24+ weeks)• Continued growth, especially of brain. Fat begins

to deposit at 32 weeks to keep baby warm at birth.

See pages 218 - 219


Sexual Reproduction Advantages and Disadvantages

See page 220 Take the Section 6.2 Quiz


6.3 Assisted Reproductive Technologies

• 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 Technologies1. Artificial Insemination - donor sperm is placed in the female.2. In vitro fertilization (IVF) - egg and sperm are collected and fertilization takes

place in a dish. Embryo(s) then placed in female’s uterus.3. Gamete intrafallopian transfer (GIFT) - eggs and sperm are collected, mixed,

then injected into the woman’s fallopian tubes.4. 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?


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