Download Sickle Cell Anemia - Woodcliff Lake School

BIOLOGY /EVOLUTION UNIT NOTES:
Biology: the study of life
Criteria to consider something alive:
1.
2.
3.
4.
5.
6.
7.
Composed of cells
Displays heredity
Reproduces
Responds to stimuli
Maintains homeostasis
Evolves and adapts
Requires energy
Viruses:
Are viruses alive???? Formulate an opinion that you can defend!
See reading:
http://science.howstuffworks.com/life/cellular-microscopic/virus-human.htm
Key points:
1. Viruses are not composed of cells. They are much, much smaller and are composed of a piece of
DNA or a related molecule called RNA wrapped in protein.
2. They can be harmless or cause disease. Viruses are everywhere.
3. They need a host cell to reproduce because they utilize the cell’s machinery to make copies of
themselves (“hijackers”) – They can’t reproduce on their own – they simply don’t have the
required parts to reproduce. They can live (without reproducing) on non-living surfaces for
hours to days.
4. Once inside a cell, they can make thousands of copies of themselves, exit that cell and enter
many other cells, repeating the process. Hence, viral infections spread quickly and are hard to
treat. There are only a few antiviral medications. (In contrast, there are many antibiotics, which
kill viruses)
DNA:
1 It is present in all living things. In our cells, DNA is kept in the nucleus
2. The job of DNA is to encode the instructions to make proteins that make up our body.
(Proteins do everything and DNA gets all the credit!)
3. DNA is made up of 2 strands and has four bases, A, C, G, T. (A:T, C:G)
4. The code of DNA is carried to the ribosomes where the proteins are made by a messenger
molecule RNA. (RNA has A,U,C,G and is single stranded)
Cell organelles: small structures within a cell which perform certain roles. Review icell and the
graphic organizer I gave you!
Mitosis vs Meiosis: 2 forms of cell division (In other words two ways cells make copies of
themselves) What is the difference? Name a cell made by each of these process (Consult the
check-off sheet I gave you!)
A change in the base sequence in DNA (ex CCGTTA is changed to CCATTA) is called a mutation.
Mutations can be harmful, helpful or neutral. This is because the protein that is made from the
altered code could be better, about the same, or worse in doing its job compared to the protein
that would have been made if the DNA had not been changed.
Plant cell vs Animal cell:
Differences: Plant cells have a rigid rectangular shape due to the presence of a cell wall. (Animal
cells are more round – they have no cell wall!) Plants cells have chlorophyll contained with
chloroplasts so they can carry on photosynthesis. Plant cells have a larger, more prominent
vacuole compared to animal cells.
Can you recognize a plant cell and an animal cell under the microscope?
Can you label a diagram like the following ones?
Animal cell:
Do you know the functions of the following organelles?
Mitochondria: Site of energy production
Cell membrane: controls exit / entry of materials
Chloroplasts: contains chlorophyll for photosynthesis Cytoplasm: jelly-like materials, fills cell
Vacuole: stores water
Nucleus: “brain”, directs cell activities, contains DNA
Ribosomes: Site where proteins are made Lysosome: Contains enzymes
Cell Wall: provides structure and rigidity
Golgi body: packages and distributes proteins
Taxonomy: the science of naming and classifying living things
Seven Level Classification System (proposed by Linnaeus):
Kingdom (Most general, largest category), Phylum, Class, Order, Family, Genus, Species
Example:
Genus: a group of closely related species
Species: organisms that can mate and produce fertile offspring (offspring that can later
reproduce)
An organism’s scientific name consists of their genus followed by their species. Ex. Homo
sapiens (the genus name is always capitalized, the species name is not!)
Re-look at the taxonomy review and self-quiz posted under resources!
Two types of cell division: Mitosis / Meiosis
All living things come from pre-existing living things.
During this process, offspring inherit genes from their parents which encode individual
characteristics or traits.
Chromosomes = strands of DNA containing genes.
Each species has a particular number of chromosomes. (Humans have 46 chromosomes which
are arranged in 23 pairs)
Mitosis: Cell division where the parent cell produces 2 identical copies of itself. Example: a
human skin or muscle cell (with 46 chromosomes) produces 2 identical “daughter” cells each
with 46 chromosomes. Cells in your body need replacement with identical cells – mitosis
accomplishes this. Bone cells, stomach cells, liver cells etc. also do this. (Some cells cannot
reproduce themselves. For example brain cells can’t – this is why brain injuries are so
catastrophic.
Meoisis: Cell division which produces 4 daughter cells, each with ½ the number of
chromosomes that the parent cell has. This is how the gametes (collective name for egg and
sperm) are produced. Ex. Within the human ovary, certain ovarian cells, which have 46
chromosomes produce egg cells are through meiosis. These eggs cells have 23 chromosomes,
one from each pair. In males, cells in the testes undergo meiosis to produce sperm, each of
which has 23 chromosomes (one of each pair). (Each egg cell produced is DIFFERENT from the
parent ovarian cell and different from the next egg cell that will be produced – if it wasn’t than
each baby a woman had with the same partner would be identical. The same is true for sperm
cells)
The egg and the sperm are united at fertilization to produce the zygote. The zygote undergoes
repeated rounds of mitosis to produce a baby in just 9 months! Differentiation also occurs
which is the process of cells becoming more specialized. For example, some cells become brain
cells; some cells become kidney cells, etc.
Cell Membrane
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•
•
•
Every cell is surrounded by a semi-permeable membrane – which regulates what gets into
and out of the cell. Semi-permeable membranes are membranes which allow some
substances to cross much more easily than others. (Remember our mini-lab, iodine
diffused across the membrane, starch did not!)
Diffusion is the process by which substances move from an area of high concentration to
an area of low concentration.
Factors affecting diffusion: (see chart!)
Osmosis:
The diffusion of water has a special name – it is called osmosis. Water, like other substances, moves
from where there is more water to where there is less water. Consider these scenarios:
1. There is 90% water outside a cell and only 60% inside a cell. Water will move inward by osmosis.
(remember water moves from where there is more to where there is less)
2. Sometimes, you must figure out where there is more water. Ex. A large salt molecule is present
inside a cell at a concentration of 20%. That same, large molecule is present outside the cell at
60% concentration. This salt molecule is TOO BIG to cross the membrane so it is essentially stuck
in its current position. It can, however, exert a pull on water which can cross the membrane.
Remember water moves from where there is more water to where there is less water. Where is
there more water? Well inside the cell there are fewer of these large molecules taking up space,
so that leaves room for more water. (Outside the cell is crowded with a lot of these bigger
molecules leaving less room for water) Water therefore moves out of the cell and the cell
shrinks a bit!
Remember the u-shaped tube experiment: (water crosses the membrane until equilibrium is reached –
an equal concentration of water on both sides!
Feedback Loops:
Organisms need to maintain homeostasis (a state of internal balance) to survive in a changing
environment. They do this in many ways. Positive and negative feedback cycles help organisms to
maintain homeostasis.
Most commonly, negative feedback systems are used.
In a negative feedback system or loop, the body senses an internal change and activates a mechanism
that reverses (or negates) that change.
Ex: Body temperature Regulation: If your body temperature increases, this is sensed by neurons in a
region of the brain called the hypothalamus. This region of the brain then sends out signals that cause
changes in the body, including increasing sweating, that will help return the body temperature back to
normal.
The body also uses positive feedback loops. (This is less common but remains an important way of
maintaining homeostasis). In this system, the body senses a change and activates mechanisms that
increase or accelerate that change.
Ex: A damaged blood vessel releases a chemical signal that attracts platelets a few to the area. These
platelets release more signals that attract thousands more platelets and eventually a platelet “plug” is
formed to stop the bleeding.
Sickle Cell Anemia
This recessive genetic disease (ss) illustrates the point that a change in DNA can have major
consequences. In this mutation, one base that is part of a gene on chromosomes 11 is changed.
People with 2 copies of this mutation (ss) have a disease called sickle cell anemia. Their bodies,
because of the wrong DNA sequence make an abnormal protein, causing there red blood cells
to become sickle shaped. These crescent moon shaped cells get clogged in small blood vessels
and often fail to reach the cells they are trying to deliver oxygen too. This leaves the person
with many serious symptoms. This disease is lifelong – remember it is encoded in every cell of
the body.
Being a carrier of the sickle cell gene (Ss) means that you have one affected allele and one
normal allele. (The term carrier only applies to recessive disease – it means that you silently
carry one copy of the gene but because it is recessive, you don’t have the disease) If you live in
Africa, this may be of befit because it helps you fight off another disease – malaria which is
carried by mosquitos. But, as we saw in the video, the risk is that you could pass down the “s”
allele to a child, and if the other parent possess down an “s” as well, the child will develop sickle
cell anemia.
This example shows that in different environments, different genes are favored and therefore
may exist more or less frequently over time.
SS might be the “preferred” genotype of someone in the US where malaria is non-existent but
Ss might be preferable in Africa where resistance to malaria is of great benefit.
Blood Types:
A cell is the basic unit of structure in the body (remember cell -> tissue (cells working together)
-> organ-> system-> organism). A red blood cell does the critical job of delivering oxygen to the
cells. Its structure is related to its function. Can you explain how?
In the event of blood loss, a transfusion is sometime necessary to maintain homeostasis.
There are four blood types: A, B, AB, and O. Your blood type is determined by the proteins
which are attached to the cell membrane of your red blood cells. If you:
1.
2.
3.
4.
Have the A protein, then your blood type is A
Have the B protein, then your blood type is B
Have both proteins, then your blood type is AB
Have neither, and then your blood type is O.
Your body recognizes and accepts familiar substances and attacks and destroys unfamiliar
things (Think of White blood cells destroying invading bacteria and viruses) Therefore, it is
necessary to match blood transfusions so that only familiar substances are given to a patient.
(Remember the body will destroy the unfamiliar and the patient will get sicker!)
Go back to the chart we did in class and review SAFE and UNSAFE transfusions! Can you predict
if a transfusion will be safe?
Blood types are inherited with each person receiving one allele form their mom and one from
their dad. The possible alleles are listed below, along with their corresponding genotypes:
(Note: the A and B alleles are co-dominant meaning they are BOTH expressed!)
Review the worksheet called “Co-dominance” and make sure you understand how to approach
Punnett squares that have to do with blood typing.
Pedigree Analysis:
A pedigree is a diagram that traces the inheritance of a disease
or condition thru generations. It is like a family tree for genetics. Keep in mind the following:
1.
2.
3.
4.
Circles are females
Squares are males
Children of a couple are listed in birth order from left to right.
Individuals with the condition are shaded in.
When labeling a pedigree with the genotypes of the family members, be sure to use the
following steps:
a. Write out each of the three genotypes and their corresponding phenotypes
b. Label the recessive individuals and then work backwards, using an individual’s
parents and children to infer their genotype.
c. If a person is either homozygous dominant or heterozygous (ex. AA or Aa), this can
be indicated A_.
Ex: This pedigree is for a recessive disease called albinism.
Step 1: AA = normal pigmentation
Aa = normal pigmentation
Aa = albino
Step 2: The recessive people in this pedigree are the ones with the disease, so here I would
have labeled the shaded shapes with “aa” (individuals 3 and 7) . Working backwards, I would
infer that individuals 1 and 2 must carry the “a” allele as each of them passed it to their child,
therefore they must be Aa. Likewise, individuals 4 and 5 must be heterozygous (Aa) for the
same reason – they have an affected child. Individual 6 is Aa or AA (A_) because although we
know she has at least one “A” we do not know her second allele.
Evolution: Change over time
An environment determines whether a trait is favorable or not.
Example: rabbits with thick fur
In a cold climate, these rabbits survive better than those with less fur. (Imagine the ones with
less fur freeze to death) The rabbit with the thick fur survive better. They reach reproductive
age and pass on their gene for thick fur. Several generations later, the gene for thick fur has
become much more common in the population as a whole.
In a hot climate, the gene for thick fur is a disadvantage. Many of these rabbits overheat and
die. They do not reproduce very much, and the gene for thick fur in this environment does not
get passed down much and becomes less common
Allele and Genotype Frequency:
Allele frequency = number of copies of the specified gene / total number of genes in the
population
Genotype [e frequency = number of individuals with the specified genotype / total number of
individuals
Recall that a genotype is made up of 2 genes:
Ex: BB, Bb, or bb.
If we are talking about the color of pea pods in a given population of plants, and we have 40
plants, then we are considering 40 genotypes (which is 80 genes!)
Take this data:
In pea plants, green color(G) is dominant to yellow color (g).
We have 30 plants: 10 are BB, 14 are Bb, 6 are bb.
(30 genotypes = 60 genes)
What is the genotype frequency of the bb genotype?
6 plants out of 30 have the bb genotype so the genotype frequency is 6/30.
What is the allele frequency of the “b” gene?
6 plants have the bb genotype (those plants each have two “b” genes, so that is 12 ‘b”
genes) and 14 Plants have the genotype Bb (these plants have one “b” each, so that is 14 more
“b” genes) 12 + 14 = 26 copies of the “b” gene.
There are 30 plants in this population, which means the total number of genes is 60.
The gene or allele frequency of the “b” allele is 26/60.
EVOLUTION: CHANGE OVER TIME
1. All life on earth traces its origin back to that very first cell which evolved on the early earth (a
very different place than today’s earth!)
It was prokaryotic, had a genetic code, a cell membrane and did not rely on oxygen!
2. From there, mutations occurred randomly over time. If the mutation allowed an organism to
survive better, then that that organism lived long enough to reproduce and therefore that trait
became more common in the population!
3. At some point, the organism’s traits were different enough to consider it a new species!
Endosymbiotic theory:
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States that the nucleus, mitochondria and perhaps other organelles began as
separate bacteria that were engulfed into other organisms and were then
incorporated as organelles!
Evolution involves the idea that all current life forms evolved from pre-existing life forms.
(The exception to the above statement is the very first cell)
Conditions on the early earth:
a.
b.
c.
d.
e.
More volcanic activity
Frequent meteor strikes
No oxygen in the atmosphere
More ocean, less land
Torrential rains
By simulating these conditions in a lab, scientists were able to prove that RNA (a related molecule to
DNA) could spontaneously form. They believe, although it has not been replicated, that an entire cell
arose from non-living material under these conditions about 3.8 billion years ago.
Geologic Timeline:
Review the sequence of events in the last 5 BILLION years!:
• http://www.bbc.co.uk/nature/history_of_the_earth#timeline
Opposing views:
Charles Darwin and Jean Baptiste Lamarck:
Review the posted document (it can be found under resources): How do species change over
time? What did each of these scientists believe? Who do we believe was right?
Natural selection: (Darwin’s idea)
• There is a natural variation among individuals in a
given species / some variations are more favorable /
more individuals with these variations survive
•
An adaptation is any inheritable characteristic that improves an organism’s ability to
survive and reproduce. Adaptations can be:
1. Structural: related to the organism’s body parts or features
2. Behavioral: related to things the organism does to help them survive
Two examples of adaptation types:
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•
Camouflage: an adaptation in which an organism’s appearance allows them to
blend into their environment, making them less likely to be killed by other
organisms
Mimicry: an adaptation that enables one species to resemble another species. (the
viceroy butterfly resembles the Monarch. Predators avoid eating the Monarch
because they are toxic. The non-toxic viceroy are also avoided by predators who
are folled into thinking they are the Monarch.
PEPPERED MOTHS:
Remember the study done in England! When the tress were light colored, lighter moths survived better
due to camouflage. They outnumbered dark moths. With the rise of the Industrial Revolution, the trees
became soot-covered and darker moths began to survive better and outnumber their lighter
counterparts. This is CHANGE OVER TIME! Evolution takes place in populations over generations, not in
one individual organism.
Spontaneous Generation: the idea that non-living material can give rise to living things. (The mud on the
banks of the Nile comes to life as frogs!) This mistaken belief was thought to be true by some people
throughout history.
We do not believe spontaneous generation occurs today. (Although keep in mind – this is exactly what
we think happened on a very different, early earth to generate the very first cell!)
Two famous experiments (one in the 1600’s and one in the 1800’s) helped disprove spontaneous
generation:
Francisco Redi: Disproved spontaneous generation by setting up the experiment below and noting the
absence of flies in the first jar as proof that meat cannot pop to life as flies. (Flies must come from
parent flies)
Louis Pasteur: Disproved spontaneous generation through the experiment pictured below. The absence of bacteria
in the first flask proved that broth cannot morph into bacteria. (Bacteria must come from parent bacteria which
entered the second flask through the air coming in the wide-open flask!)