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Cells 9:
Body cells are called somatic cells to distinguish them from reproductive (sex) cells. Of
course most of the cells in a multicellular organism, like those of humans, are somatic
cells. These cells reproduce through cell division (involving the process of mitosis) and
result in daughter cells identical in the number of chromosomes and the genetic codes for
traits. There are 23 pairs of chromosomes, for a total of 46 in each human somatic cell.
Reproduction cells on the other hand, have half as many chromosomes as the parent cell.
Reproduction cells are also called gametes. Male gametes are called sperm, and female
gametes are called eggs or ova.
Chromosome Numbers (See also: Forming the Zygote on page 3)
Since all humans have 46 chromosomes and our offspring result from the fusing of
genetic material from two individual parents, it would make sense to assume that our
offspring should have 92 chromosomes (46 from each parent). To ensure that the number
of chromosomes in our species is not doubling from generation to generation, gametes
(reproduction cells) must have their chromosomes halved. Meiosis is the name of the
process which ensures that gametes have half the number of chromosomes as the parent.
The reproductive cells, or gametes, are the only cells that undergo meiosis. Since meiosis
cuts the number of chromosomes in
half, the process is sometimes called
Reducing Human Chromosome Numbers
“reduction division”. Each human
m
gamete contains 23 chromosomes –
fro
46 2n
diploid
half the genetic material of the parent.
Cells containing half the number of
to
chromosomes as the parent are called
23
23 n
haploid, and are symbolized with a
single n. On the other hand, somatic
haploid
23
23 23
23 n
cells with the full set of chromosomes
are called diploid and are symbolized
as 2n.
Homologous Chromosomes
Each diploid somatic cell has a corresponding pair of chromosomes which share in
common a similar set of gene trait codes. What this means is that chromosomes are
paired up so that partnered chromosomes have the same gene trait variations, on the same
gene segments, as their partner. This does not mean that the chromosome pairs, called
homologous chromosomes, are identical. Homologous chromosomes are similar. For
example, a homologous pair may have your mother’s gene variation of eye color (lets say
she has blue eyes) on one chromosome, and your dad’s eye color gene code (lets say he
has brown eyes) on the other partnered chromosome. When chromosomes are reduced to
half of the parent (n), the split initially will occur between the partnered homologous
chromosomes. This means, in our example, that some of the resulting gametes (in fact
half of them) will have the gene for blue eyes, while the rest will have the gene for brown
eyes.
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Mitosis vs. Meiosis
Before we cover the stages of meiosis, it is important to realize that many stages of
mitosis are similar. In both mitosis and meiosis, sister chromatids (recall that these are
identical), must join together (resembling an X). The key difference between the two
processes is that when the sister chromatids split in mitosis, the homologous pairs divide
in meiosis. The split between chromatids in meiosis does not occur until later.
Review of Mitosis (For more details refer to Cell Division on page 8)
Recall: For most of its life, the cell is in interphase and exists as a working cell. Late in
interphase the chromosomes are replicated.
Prior to mitosis the chromosomes have been copied or replicated, and have begun to
shorten and thicken. When mitosis begins the sister chromatids join up (each sister with
identical genetics) and begin to be pulled to the cells middle by spindle fibers. After
lining up in the middle of the cell, the fully formed spindle pulls the sister chromatids
apart and towards the poles*. (This marks the first significant difference between mitosis
and meiosis).This ensures that identical genetic information is heading towards each
opposite end of the cell. After this the cell begins to pinch in and two new nuclear
membranes begin to form. (Recall: the process of dividing the cytoplasm into two
identical daughter cells is called cytokinesis). When the cell divides, two genetically
identical, diploid (2n) daughter cells are formed. (Meiosis on the other hand, will form
four haploid (n) daughter cells).
Mitosis
Interphase
Prophase
Metaphase*
Anaphase
Telophase Daughter cells
Meiosis
There are two phases of meiosis, meiosis I and meiosis II. In meiosis I, the homologous
chromosomes are divided, and then the cell divides for the first time. Since the
homologous chromosomes are corresponding rather than identical the daughter cells in
meiosis I are not the same. (Some of your gene trait variations are in one cell and some
are in the other, but all the information necessary to retain the human genome are in
both). In meiosis II the homologous chromosomes (which are still attached to their sister
chromatids at the end of meiosis I) are split between the sister chromatids and the final
cell division results in four haploid daughter cells (gametes).
The Stages of Meiosis
During interphase, chromosomes of reproductive cells, replicate to form joined sister
chromatids (resembling an X). These will shorten, thicken and begin to move to the
center of the cell in prophase. In metaphase the sister chromatids will arrange themselves
in the center, opposite of their homologous pair (with similar genes), ready to be pulled in
the opposite direction (but do not split apart). (*Recall, in mitosis the sister chromatids
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are all in a line in the center, readying to be split apart). In anaphase, the homologous
chromosomes (each still joined to their sister chromatid) will be pulled by the spindle to
the opposite poles of the cell. Telophase will produce a split which results in two
daughter cells with corresponding (but not identical) genes. Each of these cell will
contain joined sister chromatids. These will need to be split in meiosis II.
Meiosis I
Interphase
Prophase
Metaphase*
Anaphase
Telophase Daughter cells
Meiosis II is very similar to mitosis in that the joined sister chromatids (Xs) will line up
in the center and then separate. The key differences are that meiosis II starts with two
cells, each with half the number of sister chromatids, and the sister chromatids, from both
cells split, the cells divide into four haploid daughter cells (gametes).
Meiosis II
Forming the Zygote: From Haploid back to Diploid Fertilization refers to the joining
or fusing of two gametes. Recall that offspring result from the fusing of genetic material
from two parents. Meiosis halves the number of chromosomes so that each gamete is
haploid. When two haploid daughter cells (n) combine during fertilization, the resulting
diploid cell contains a complete set of chromosomes (2n).
In humans, 23 chromosomes from the male gamete, called a sperm, combines with 23
chromosomes from the female gamete, called an egg, to form a diploid cell with the
complete set of 46 chromosomes. The first cell of fertilization is called a zygote. In other
words, a haploid sperm cell and a haploid egg cell combine to form the first diploid cell
called a zygote. Once the zygote forms, the new organism will undergo cell division to
increase in size.
Variation
You do not look like the person next to you because of variation amongst gene traits.
Some noticeable human gene trait variations include, eye color, hair color, hairlines
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(which can be straight or widow’s peak), earlobes (attached or unattached), little finger
shape (bent toward ring finger or straight), thumb shape (curved or straight), and nose
shape (straight and small or totally huge and crooked – joke). Scientists refer to the
different forms or variations of the same genes as alleles.
The dividing of homologous chromosomes in meiosis results in species variation in the
fist place. This is because different gene variations end up in the daughter cells which
result from the first (meiosis) cell division. Consider that the division of homologous
chromosomes, producing different gametes, occurs in each parent. Combine this with the
huge variation of genes that exists in our species -from knobby knees to double chins and it is not hard to see how the the mixing and matching of two parent gametes results in
widely different looking offspring, from family to family, throughout the globe.
Dominance
Somewhere on one of your chromosomes there is a gene for hairline, on its paired
chromosome there is another gene for hairline. It is possible that one gene in the
chromosome pair will have an allele for widow’s peak, while the gene on the other
chromosome will have an allele for a straight hairline. In this case one allele will
overwrite the other. The victorious allele is called the dominant allele. The allele that is
overwritten is called the recessive allele. In other words, the dominant allele will express
the trait (and show up in your appearance) while the other will remain hidden (possibly to
show up in a later generation). In hairline the dominant allele is for widow’s peak, so if
you have a straight line allele on the homologous chromosome, you will not know it,
because it will have been
overwritten.
Human Karyotype
During metaphase scientists have
been able to take magnified picture
of individual chromosomes. By
matching up pictures of the
homologous pairs (they are similar
in shape and size as well as gene
variations), they have created what is
known as the Karyotype – the
arrangement of homologous
chromosomes from a body cell. The
human Karyotype contains 23 pairs
of or 46 chromosomes.
2n female
parent cell
(XX)
(a) All the eggs have a single X chromosome.
X chromosome
2n male
parent cell
(XY)
Y chromosome
(b) Half the sperm
cells have a single
X chromosome.
Half the sperm
cells have a single
Y chromosome.
Upon close examination of the Karyotype scientists were able to determine that only 22
pairs of chromosomes were homologous – the 23rd pair was of different sizes. These two
chromosomes are the gender or sex chromosomes because they determine whether the
individual is a male or a female. The two types of sex chromosomes are the X
chromosome and the smaller Y chromosome.
Males have an X chromosome and a Y chromosome, and females have two X
chromosomes. In other words the 23rd pair of chromosomes for males is XY and for
females it is XX. Recall, in meiosis, chromosomes are halved. For males this means that
one gamete will have and X chromosomes and the other gamete will have Y
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chromosome. For females the pair that is divided is XX, so that both gametes have an X
chromosome. In other words male gametes (sperm) can contain X chromosomes or Y
chromosomes, while female gametes (eggs) always contain X chromosomes.
Zygotes and X and Y Chromosomes
Since female gametes only contain X chromosomes, male gametes always determine
gender. If a sperm with Y chromosome fertilizes the egg, the zygote will have and XY
chromosome pair and the offspring will
be a male. If a sperm with an X
XY male
female XX
Parents
chromosome fertilizes the egg, the
zygote will have an XX chromosome
pair and the offspring will be female.
Unlike females which have 23 pairs of
Gametes
X
Y
X
(matching) homologous chromosomes,
males only have 22 pairs that are
homologous. This is because and XX
pair of chromosomes match up, but the
XY pair (male pair) does not. Since X
Zygotes
XX
XY
and Y chromosomes do not entirely carry
female offspring male offspring
matching genes (some of the genetic
material on the Y chromosome is
missing), males have what is known as sex-linked characteristics. The missing
information on the Y chromosome of the XY male determining pair, leads to
characteristics in males that are rarely seen in females. These characteristics include
baldness, color blindness and the blood clotting disease hemophilia (which can lead to
excessive bleeding).
Atypical Meiosis (Not on Final Exam)
Meiosis is a complicated process that happens correctly most of the time, but things do go
wrong on occasion. One of the most common errors occurs when the homologous
chromosomes do not separate properly. This is called non-disjunction and results in
gametes with the wrong number of chromosomes. Instead of a 23 to 23 split, one gamete
only receives 22 chromosomes while the other receives 24 chromosomes.
Chromosome Disorders (Not on Final Exam)
If a nondisjunction 22 chromosome gamete fuses with a normal 23 chromosome gamete
the resulting zygote will only have 45 chromosomes (instead of 46). If a nondisjunction
24 chromosome gamete, joins with a normal 23 chromosome gamete a 47 chromosome
zygote will form. Down syndrome is a fairly common disorder which results from a 47
chromosome zygote.
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46
46
normal meiosis
nondisjunction
23
23
normal meiosis
nondisjunction
23
22
23
22
24
normal meiosis
24
22
22
24
This page
is not on
the final
exam.
24
fertilization
45
abnormal chromosome number in the zygote
The 22 chromosome, 24 chromosome split can get quite complicated for male gametes,
because sometimes the nondisjunction occurs with the XY chromosome. Instead of
dividing between the two gametes, one sperm receives both the XY together (24
chromosomes) while the other receives neither (22 chromosomes). If the nondisjunction
24 chromosome gamete with an XY fertilizes and normal egg, containing a single X
chromosome, the resulting zygote will have an XXY chromosome (an extra X). A zygote
with XXY will have the disorder known as Klinefelter syndrome. If the gamete with 22
chromosomes (with neither and X nor Y) fertilizes a normal egg, with a single X
chromosome, a zygote with a single X chromosome will form (in other words the egg
received neither an X nor Y from the sperm). A zygote with a single X chromosome will
exhibit Turner syndrome.
A 22, 24 chromosome split can also happen in such a way that one set of female gametes
has no X chromosomes (22 total) while the other set has a both X chromosomes (24 total
with both XX). In other words, something can go wrong in such a way that the XX does
not split up; hence, one set of gametes receives both chromosomes (XX) and the other set
has none. If an XX egg is fertilized by X containing sperm, a zygote containing XXX will
form. A zygote with an extra X chromosome (XXX) will develop into what is known as a
trisomic female.
XX
XY
XX
XY
normal
meiosis
nondisjunction
nondisjunction
normal
meiosis
X
X
XY
XXY
X_
Klinefelter
Syndrome
Turner
Syndrome
XX
XXX
trisomic
female
X
Y
X_
Turner
Syndrome
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Some Final Exam Review
DNA to Protein (For more, refer to Review of Protein Synthesis on p.11)
The DNA molecules which make up a chromosome resemble a twisted ladder. Untwisted
the base pairs make up the rungs of the ladder. A gene can be thought as a segment of the
ladder. In other words, a gene is a segment of DNA.
untwisted
DNA
DNA "ladder"
DNA
gene
Most people have a generalized sense of “genes”. For example, you may be tall and lanky
(built for speed) while your friend may be stocky and more powerfully built. In other
words you and your friend have different traits. The answer to why you and your friend
are so different is commonly answered, “It’s in the genes”.
While it is true to state that the difference in characteristics between you and your friend
is in the genes, it is also true to state that it is in the proteins as well. Proteins form your
body’s structure and perform nearly all the work involved in being alive. So you see; it is
how proteins are put together that determines whether you have fast long muscles or
more powerful stout muscles. In fact proteins determine all of your traits including the
most observable ones like eye color, hair texture, and skin tone.
So, what do genes have to do with proteins? A gene is a code built into DNA molecules
which provides instructions for your cells to produce a specific protein.
Building a protein from a gene segment of DNA is a multistep process. Key to this
process is the formation of a molecule very similar to DNA called RNA. In fact RNA
looks exactly like half a segment of DNA (or half of the ladder). This is because RNA is
a copy of one half or one side of the gene segment of DNA.
In order to construct the RNA molecule, the gene segment of DNA must “unzip” (split
down the middle). Once split, one half of the DNA ladder is used to construct a copy of
the other half. Once constructed, the copied half, now called RNA, must travel out of the
nucleus into the cytoplasm.
In the cytoplasm, ribosomes (which are housed in the rough endoplasmic reticulum) have
the job of “reading” the RNA code and constructing the protein. The instructions provide
ribosomses with the correct sequence of amino acid links (the building blocks of
proteins) necessary to assemble the correct protein molecule.
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Cell Division
Eventually all cells must divide. Cell division involves two processes; first, mitosis
divides up two sets of identical chromosomes, and then cytokinesis splits one cell into
two identical daughter cells. But, before this the cell is in interphase.
Most of a cells life is spent as a “working cell”; performing such routines as converting
glucose and oxygen into energy, building proteins and ridding itself of waste. This stage
is called interphase.
Near the end of interphase, chromosomes will replicate (clone) and join together in
preparation for cell division. This marks the beginning of mitosis.
The Stages of Mitosis
Replicated chromosomes shorten and thicken at the
end of interphase. These are now called chromatids.
At the start of mitosis the each pair of identical
chromatids will join at the middle forming an “X”
like structure called a sister chromatids.
late in interphase
1. Prophase: In the first stage of mitosis (called
prophase
prophase), the nuclear membrane disappears and a
spindle of fibers grows out of structures called
centrioles. The spindle attaches to the sister
chromatids and begins to pull them towards the
center of the cell.
metaphase
2. Metaphase: In the second stage of mitosis
(called metaphase) the spindle is a fully
formed network of fibers. It pulls the sister
chromatids into a line-up across the center of
the cell.
anaphase
3. Anaphase: In the third stage of mitosis (called
anaphase), the spindle splits the sister chromatids
apart, pulling each partner to the opposite ends of the
cell. (Note: Once apart the chromatids are once again
called chromosomes).
4. Telophase: In the fourth and last stage of mitosis
telophase
(called telophase), a series of events occur which form two identical
nuclei: the spindle disappears, and the chromosomes lengthen and
get thinner as two new nuclear membranes begin to reform around
them. Additionally, the cell will begin to pinch in at the middle
marking the beginning of cytokinesis.
Cytokinesis
Cytokinesis finishes cell division by dividing out two identical daughter cells: The
membrane pinches in the cytoplasm between the two nuclei eventually splitting off the
two daughter cells.
cytokinesis
Stem Cells and Mutations
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Stem Cells: The Future of Medicine?
Recall, in cell division, meiosis halves the number chromosomes to produce haploid daughter
cells called gametes. During fertilization a gamete (sex cell) from each parent fuses together
forming a single diploid cell called a zygote. After several cell divisions a ball of unspecialized
cells called an embryo is formed. The cells of an embryo are called unspecialized because they
have not yet developed into specialized cells like liver tissue cells, bone cells or blood cells. What
is key to understand about the zygote and the cells of the developing embryo is that the DNA
instructions they contain allows them to become any of the over 200 specialized cells of your
body. The process of growing from unspecialized cells into many different specialized cells is
called differentiation.
Physicians and medical researchers have always been looking for suitable alternatives to organ
transplants. Currently, people who experience organ failure have two main worries. First of all,
organs for transplant are rare and may not be available in time. Secondly, the body will reject the
organ unless the patient is given immunosuppressant drugs (these are harmful, often cancer
causing drugs, which keep the immune system from attacking the transplanted organ).
Embryonic stem cells are of high interest to physicians because the cells of the embryo can
become any type of cell in the body. Hence, an organ could potentially be repaired using
embryonic stem cells. Using embryonic stem cells to regenerate failed organs would eliminate the
need for a donor list, but two problems would still exist. The first problem with embryonic stems
cells is that they must be harvested from an embryo, and many people are opposed to their use.
The second problem is the same as it is for transplanted organs – the new cells are not from the
patient, so they will be rejected by the body’s immune system if drugs are not taken.
The problem for medical scientists is to find cells in adults that can be reprogrammed to act like
embryonic stem cells. If these cells could exist then the next step would be to clone them.
The closest thing to an embryonic stem cell in an adult is called and adult stem cell or a somatic
stem cell. Somatic stem cells are usually organ specific. For example, a somatic stem cell that is
found in the heart can only grow into the different types of cells specific to the heart. Hence, a
somatic stem cell cannot function like an embryonic stem cell unless it can be reprogrammed to
act like one.
One possible way to re-program a somatic stem cell is to remove its nucleus, and place it in an
empty egg cell (with no chromosomes). Once the nucleus is set inside its new house, a culture
media (a mix of growth chemicals) is added. Next, cell division is electrically stimulated. This
method borrows from the cloning technology which produced “Dolly the Sheep”.
At this time, scientists have only been able to clone a human cell to the point where cell division
produces four to six cells. In order to produce patient-specific cells (for regenerating of personal
organs) the cell group would need to grow into a much larger ball of cells called a blastocyst. If
produced, the blastocyst would become the “toolbox” of cells needed to regrow hearts, repair skin
tissue, fix limbs (so they do not need to be amputated), and reverse blindness.
A Mutation Causes Cancer
Recall that the key links in DNA are the base pairs which make up the rungs or steps in the
ladder. When it comes to DNA, two questions have long concerned scientists: (1) what would
happen if the base pairs were changed in some way? And (2) how could these changes in the
DNA structure occur?
It turns out that there are two possibilities for changing DNA. First, the rungs can be re-ordered
during sequencing. This means that late in interphase, when the DNA is being replicated, some of
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the base pairs can change places. The other change in DNA, can occur if aggressive unwanted,
molecules attach themselves to the base pairs.
What would happen if DNA was altered by one of the changes mentioned above? Most often
these changes would either be quickly repaired, or a “filter system” would cause the cell to
destroy itself before the next cell division could occur. If, however, the DNA was altered and the
cell did survive to divide, then the change in the DNA or genetic code of the cell would be called
a mutation.
Cancer is not a mutation, but a response to one. The cell cycle is controlled by the DNA
instructions in the genes of each type of cell. If something goes wrong – like a base pair changes
places or is altered – the cell may lose its ability to divide properly. Cancer is a disease where the
cells divide uncontrollably. The mutation in this case has occurred in the DNA which controls the
cell cycle.
Recall that gene segments of DNA code for the construction of a protein. At some time during the
cell cycle a protein is built which singles the end of normal cell division – most somatic cells can
only divide so many times before they become dysfunctional and die off (or accumulate in the
body somewhere). Cancer cells acquire a mutation which blocks the protein which normally ends
the lifespan of cell division. The result is that cancer cells become “immortal”, dividing faster and
more often then normal cells.
Most cancers are believed to be caused by the accumulated damage done by years of exposure to
external toxins. (Cigarette smoke is a common source of many toxins). As these toxins begin to
pile up in cells they eventually penetrate the nucleus. Once inside the toxins begin to harass the
gene segments of DNA which make up chromosomes. Toxins damage genes by attacking the
base pairs of DNA; attaching disruptive molecules that muck up the genetic information. If the
cell cannot repair the “molecular muck” it becomes a mutation. If the mutation allows the cell to
continue to divide and grow faster than a normal cell lifespan then the mutation has caused
cancer.
As cancer cells continue to divide, they form an abnormal mass is called a tumor. Sometimes
your body manages to close of the area of a tumor stopping it from further growth; these are
called benign tumors. If the tumor cannot be closed off by your body, it will grow and grow,
these tumors are called malignant.
Genetic Disorders
When something to do with DNA goes wrong, often the end result is that a protein is made
improperly (or not at all). A person with diabetes, for example, has a problem properly
constructing the molecule insulin. Why does this happen? The DNA in that person’s cell has been
altered in some way so that the instructions are incomplete. This is the same for all genetic
disorders.
Did you know? Insulin is hormone which tells your body when you are well fed, causing the liver
and muscle cells to store glucose as glycogen.
Some mutations scientists have detected seem to have no real effects at all the body, these are
called neutral mutations. In rare occasions mutations have been desirable, these are called
beneficial mutations. (For example, seven women on the African continent were recently
discovered to be immune to HIV. Scientists believe a mutation has altered their DNA to fight off
the deadly disease AIDS). Many mutations that have led to genetic disorders including cystic
fibrosis, diabetes, sickle cell disease, and Huntington’s disease. These are called harmful
mutations.
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Sexual Vs Asexual Reproduction (A Review)
One striking outcome of sexual reproduction (in comparison to asexual reproduction) is the large
variety of traits in the offspring (this is called variation). Since, you received 23 chromosomes
from each parent for a total of 46 chromosomes; you are blend of different gene trait
characteristics passed along to you – the mesh of which will have some characteristics that are
obviously similar to each of your parents, but many more that are much more difficult to put a
finger on. Asexual reproduction on the other hand is basically cloning; i.e. a strawberry plant is
identical to its parent.
Types of Asexual Reproduction
In binary fission, the parent cell duplicates itself (in a manner similar to mitosis), then pinches in
at the middle, splitting into two identical (but smaller) daughter cells. Single-celled organisms
like bacteria and protists (like amoeba) undergoe binary fission.
In budding, the offspring begins as a small growth (called bud) on the side of the parent before
breaking off as an identical daughter. Budding occurs in single-celled creatures like yeast.
☻ Some plants like strawberries send out runners or shoots which eventually root themselves and
start to grow on their own. This is called vegetative reproduction. (VR occurs in commonly in
potatoes). ☻ If the arm of a starfish is severed off, the larger portion will regrow the single arm,
and the smaller portion will regrow several arms and a center – two identical starfish will emerge.
This is called fragmentation. ☻ Spores are like seeds except they are cells produced by cell
division. Organisms that produce spores include many types of fungi (puff balls, moulds, etc).
This type of asexual reproduction is called spore formation.
The main advantage of asexual reproduction is that large numbers of offspring can be
produced.
DNA and Protein Synthesis
The DNA in each gene provides the instructions to make a specific protein. Proteins in turn are used to help
grow and repair every type of cell in your body. Recall that the actual production of a protein follows a
specific path: First the gene segments of a DNA molecule (contained in a chromosome) unzip. RNA is then
constructed from one half of the unzipped DNA segment. Once constructed, RNA contains the codes for
making the protein.
cytoplasm
gene
segment
of DNA
a gene segment
of DNA "unzips"
RNA is constructed
from half of the DNA
RNA
Secondly, the RNA is sent out (from the nucleus) into the cytoplasm where ribosomes read the RNA code
and then construct the protein by piecing together amino acids.
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ad
re
Amino Acids
ribosomes
RNA
ribosomes read
the RNA code
a protein is
constructed
ribosomes assemble
the amino acids
Electricity Formulae
Figure 2
_
+____
+_
_
+__ _
+ __
+ +__
+ _
+_ _+ _
_+ +
A
+ +__
+
+_ _+ __
_+ +
_
_+
_
+
_+ ++ __
_
_ +_ _+ __
_+ +
B
V = IR
P = VI
R= V
I
E = Pt
I= V
R
E = VIt
or
V - Volts (V)
I - Current (Amps or A)
R - Resistance (ohms or
P - Power (Watts or W)
t - time (seconds)
E - Energy (joules or j)
C
)
(Refer to Figure 2): Which picture represents the definition of charging by friction:
Charging by friction: An object that attracts electrons (usually plastic, rubber or animal fur) is rubbed
on another object.
(Refer to Figure 2): Which picture represents the definition of charging by induction:
Charging by induction: When a charged object is brought near (but not touching) another object, it
induces a charge attraction (positive charges near negative charges) or a discharge (spark).
(Refer to Figure 2): Which picture represents the definition of charging by conduction: Charging by
conduction: When an accumulation of electrical charge, within one object, discharges (sparks) upon
touching another object.
Determing resistance from an OHM's LAW graph:
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Find a an easy point on the line.
Interplote the graph to find V and I.
(For the point shown V = 5 V and
I = 0.20 A).
R= V
I
R= 5V
0.2 A
Sub into
i.e.
= 100
5
V
o
l
t
a
g
e
(V)
4
3
2
1
0
0.05 0.10 0.15 0.20 0.25
Current (A)
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