Download Macromolecules - Essentials Education

THEME 1
Macromolecules
THREADS
Organisation
Selectivity
Energy Flow
Perpetuation
Evolution
Human Awareness
WORKSHEETS
1
The structure of DNA
2
Chromosomes are made up of genes
3
DNA and protein synthesis
4
Structure and function of protein molecules in cells
5
The importance of polysaccharides and lipids
6
DNA replication
7
Enzymes
8
DNA and protein evidence for evolution
9
Mutations
10
Genetic manipulation
11
Some social consequences of genetic
manipulation
12
Multiplying and sequencing DNA
KEY IDEAS
Students should know and understand the following:
M1.
The chemical unit of genetic information in most organisms is DNA
M2.
The structural unit of information in the cell is the chromosome
M3.
The functional unit of information on the chromosome is the gene
M4.
The flow of information from DNA to protein is unidirectional in most
organisms
DNA Î RNA Î protein
M5.
The three-dimensional structure of a protein is critical to its function
M6.
Polysaccharides and lipids are important macromolecules in cells and
organisms
M7.
Specific base-pairing is the mechanism of DNA replication
M8.
Enzymes are specific for their substrate
M9.
Molecular recognition is an important property for life processes
M10. Enzymes increase reaction rates by lowering activation energy
M11. Macromolecules are used as energy reserves
M12. DNA carries genetic information from one generation to the next
M13. The universal presence of DNA is strong evidence for the common ancestry of
all living things
M14. DNA and protein sequences usually show greater similarity between closely
related groups of organisms than between distantly related groups
M15. Change in the base sequence of DNA can lead to the alteration or absence of
proteins, and to the appearance of new characteristics in the descendants
M16. Human beings can manipulate DNA
M17. Human beings can sequence even small amounts of DNA
© SSABSA 2002 (reprinted with permission)
© Crierie A. and Greig D. 2004 All rights are reserved, copying is prohibited by law.
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SACE 2 BIOLOGY Essentials WORKBOOK
Worksheet 1
The structure of DNA
DNA stands for ‘deoxyribonucleic acid’. This molecule is found primarily in the nucleus of cells. It is a
double stranded molecule with the strands wound around each other to form a double helix. The
molecule is made up of repeating units called nucleotides. A single nucleotide is made up of three
components: a deoxyribose sugar, a phosphate and an organic base.
The diagram below is a representation of 2 nucleotides bonded together.
Bases
M
A
T
Deoxyribose
sugar
Phosphate
Weak hydrogen bonds between bases
C
G
A
T
G
C
A
C
C
There are four organic bases found in DNA: Adenine, Thymine, Guanine and
Cytosine. The letters A, T, G and C represent these bases.
A single strand of DNA is a sequence of nucleotides joined together with
alternating phosphate and sugar components. The double helix molecule consists
of two complementary strands that are joined by hydrogen bonds between the
bases. The bases always pair in specific ways:
Adenine always bonds with Thymine
Guanine always bonds with Cytosine
Thymine always bonds with Adenine
Cytosine always bonds with Guanine
A
T
T
G
G
A
T
C
G
A
T
A
T
G
A
The adjacent diagram shows the double helical model for DNA first proposed
by two scientists Watson and Crick in 1953.
C
T
1. Write a concise statement to explain each of the following terms:
complementary
……………………………………………………………………………………………...
DNA
………………………………………………………………………………………..….…
macromolecule
………………………………………………………………………………………..….…
monomer
………………………………………………………………………………………..….…
nucleic acid
………………………………………………………………………………………..….…
nucleotide
………………………………………………………………………………………..….…
organic
………………………………………………………………………………………..….…
polymer
………………………………………………………………………………………..….…
base
………………………………………………………………………………………..….…
deoxyribose sugar
………………………………………………………………………………………..….…
phosphate
………………………………………………………………………………………..….…
© Crierie A. and Greig D. 2004 All rights are reserved, copying is prohibited by law.
7
Worksheet 1 THE STRUCTURE OF DNA
2. The following sequence of bases was found in a segment of DNA
A A G G C T T G C
Write the sequence of bases that would be found in the complementary strand.
……………………………………………………………………………………………………………………….
3. Name the four major organic bases found in DNA.
………………………………………………………………………………………..……………………………...
4. Write down the four possible base pairings in DNA.
………………………………………………………………………………………..……………………………..
5. If a sequence of DNA has 30% guanine bases in it what percentage of thymine would there be?
………………………………………………………………………………………..……………………………..
6. Refer to the diagram below.
Sugar
Base
Phosphate
Sugar
Phosphate
Sugar
Base
Base
Phosphate
Sugar
Phosphate
Base
(a) Circle a nucleotide in the representation of a strand of DNA shown above.
(b) How many nucleotides are shown in the diagram? ……………………………………………………….
7. Use the figure to label A B C and D in the diagram below.
A
A
T
B
C
D
A
…………………………………………………………………………………………………………………
B
………………………………………………………………………………………..………………………..
C
………………………………………………………………………………………..………………………..
D
………………………………………………………………………………………..………………………..
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SACE 2 BIOLOGY Essentials WORKBOOK
Worksheet 2
M
Chromosomes are made up of genes
Chromosomes are thread-like structures made up of DNA and proteins call histones. These structures are
found in the nucleus of eukaryotic cells and are visible as the cells start to divide. The chromosome
number is constant for each species, e.g. 46 in humans, 48 in a chimpanzee, 40 in a mouse and 38 in
cabbage. Chromosomes in non-dividing cells are single stranded and the DNA is not condensed, that is,
the DNA is spread out to make it easier to access genes in transcription, an important process in protein
synthesis and replication, where another copy of the DNA is made. When the chromosomes are visible
during the Prophase stage of mitosis and/or meiosis they appear double stranded. This doubling has
occurred as the DNA has replicated in order that new cells can receive their complement of DNA.
A gene is the unit of heredity. Genes represent sequences of the bases A T G and C on chromosomes and
code for protein molecules or parts of protein molecules. Each gene is found on a particular chromosome.
Genes prescribe the features of an organism: green eyes, skin colour or the shape of a nose. In a human
with 46 chromosomes it is thought that there are around 40,000 genes, each chromosome containing
hundreds or thousands of genes.
A single gene usually contains between 300 to several thousand bases. Each gene has a start and a finish
to signal where transcription begins and ends.
The diagram below shows schematic representations of some human chromosomes and some of the gene
locations that have been identified.
2
3
Familial
Retinitis
Colon Cancer Pigmentosa
7
9
11
12
Cystic
Fibrosis
Malignant
Melanoma
Sickle Cell
Anemia
PKU
14
Alzheimer's
Disease
17
Breast
Cancer
The human genome project.
This is a project that was first proposed around 1987. Its aim was to map the entire sequence of genes to
chromosomes and sequence the human genome. The figure above illustrates some of the known gene
locations (loci). In Adelaide a group of scientists at the Women and Children's Hospital is involved in
studying chromosome 16. This overall mapping is a major undertaking as there are approximately 3
billion building blocks or nucleotides in the total genome. The first stage was completed in about June
2000.
This photograph shows a typical set of human
chromosomes, which was taken from a prepared slide
using a light microscope.
The images have been cut out and pasted together to show
the homologous pairs. Until recently this was done with
scissors, it is now done with computer software They are
generally numbered and arranged from longest to shortest.
The sex chromosomes are bottom right of this photo.
This is the male set of chromosomes or karyotype. A female
has two copies of the longer (X) sex chromosome
instead of one long (X) and one short (Y).
© Crierie A. and Greig D. 2004 All rights are reserved, copying is prohibited by law.
Worksheet 2 CHROMOSOMES ARE MADE UP OF GENES
9
1. Write a concise statement to explain each of the following terms:
. chromatid
……………………………………………………………………………………………...
chromosome
……………………………………………………………………………………………...
gene
……………………………………………………………………………………………...
genome
……………………………………………………………………………………………...
2. In what organelle are the chromosomes found in eukaryotic cells? ………………………………………
3. Why are the chromosomes not usually visible in non-dividing cells?
……………………………………………………………………………………………...………………………
……………………………………………………………………...………………………………………………
4. Explain the differences between DNA, genes, chromosomes.
……………………………………………………………………………………………...………………………
……………………………………………………………………...………………………………………………
5. What does it mean to say that a gene is linked to a chromosome?
……………………………………………………………………………………………...………………………
……………………………………………………………………...………………………………………………
6. Explain the significance of different species having different numbers and types of chromosomes?
……………………………………………………………………………………………...………………………
……………………………………………………………………...………………………………………………..
7. Approximately how many genes are there;
(a) on one human chromosome?
………………………...……………………………………………….
(b) in the human genome?
………………………...……………………………………………….
8. Scientists have known for a considerable period of time that the gene for colourblindness is on the X
chromosome.
(a) Suggest how it was discovered that this was linked to the X chromosome.
……………………………………………………………………………………………...………………………
……………………………………………………………………...………………………………………………
(b) Genes like this are said to be ‘X-linked’ and the characteristics are said to be sex-linked. Explain
why this is so.
……………………………………………………………………………………………...………………………
……………………………………………………………………...………………………………………………
9. Explain what it means to say that the structural unit of information in an organism is the chromosome.
……………………………………………………………………………………………...………………………
……………………………………………………………………...………………………………………………
……………………………………………………………………………………………...………………………
……………………………………………………………………...………………………………………………
© Crierie A. and Greig D. 2004 All rights are reserved, copying is prohibited by law.
10
Worksheet 3
SACE 2 BIOLOGY Essentials WORKBOOK
DNA and protein synthesis
Genes on the DNA code for a specific sequence of amino acids (aa) that comprise a polypeptide. Several
poypeptides usually make up a protein. They can also code for the production of an RNA molecule.
Protein synthesis requires two steps: transcription and translation.
M
Three main nucleic acids are involved.
DNA:
provides the template for the production of the mRNA.
mRNA:
transcribed from the DNA and provides a sequence of codons that are able to be
translated into a sequence of amino acids on the ribosomes.
tRNA:
there are more than 20 different types of these, each one capable of carrying only one
type of amino acid.
Transcription
This process occurs in the nucleus of a cell and is where the DNA template acts as a code to transcribe a
gene segment of DNA bases into a working copy of mRNA. The enzyme involved is called RNA
Polymerase.
The diagram below shows the process of transcription.
A
T
C
G
RNA polymerase
TA
Nucleotides
used to assemble
the mRNA
G
CG
C
T
A
U
T
C
C
U
C
A
U
A
C
G
DNA Template
G
C
A
G
C
G
C
C
U
UA
T
U
A
T
C
Growing mRNA strand
C
C
T A
U
G
C
U
A
T
C
T A
CG
T
A
mRNA nucleotides in the nucleus are binding to the exposed DNA bases to form a working copy of the
gene that will be able to be translated on the ribosomes to form protein.
Translation
Is a process where the codon sequence on the mRNA is translated into an amino acid language. tRNA
molecules carry specific amino acids into position as the anti-codon of the tRNA links with the codon on
the mRNA.
The next diagram shows the process of translation.
© Crierie A. and Greig D. 2004 All rights are reserved, copying is prohibited by law.
Worksheet 3 DNA AND PROTEIN SYNTHESIS
Leucine
Serine
11
Growing polypeptide chain
tRNA molecule
Anti codon
A
A
U
U
C
A
U
U
A
A
G
U
codon
mRNA molecule
ribosome
In the diagram above, leucine and serine are the first two amino acids that are joined together by peptide
bonds to start the polypeptide or protein.
The steps involved in protein synthesis can be set out as follows.
1.
The double helix of the DNA unwinds and unzips at the required gene site exposing the nitrogenous
bases on the template.
2.
mRNA nucleotide bases (A U G C) attach to the exposed DNA bases with the assistance of the
enzyme RNA polymerase.
3.
Once the sequence for the mRNA has been completed, the mRNA is released and moves out of the
nucleus into the cytoplasm.
4.
The DNA strands will rejoin and recoil themselves to form the double helix.
5.
The mRNA molecule attaches to the ribosomes in the cytoplasm.
6.
Specific amino acids combine with their appropriate tRNA molecules.
7.
The ribosome moves along the mRNA molecule attaching the appropriate tRNA anti-codon to the
codon on the mRNA.
8.
The amino acids join together to form a polypeptide sequence.
9.
When a stop codon is reached the translation is complete.
10. The protein breaks away and is ready for use within the cell, or to be packaged and secreted from
the cell.
1 Write a concise statement to explain each of the following terms:
amino acid
……………………………………………………………………………………………
anti-codon
……………………………………………………………………………………………
codon
……………………………………………………………………………………………
RNA polymerase
……………………………………………………………………………………………
mRNA
……………………………………………………………………………………………
ribosome
……………………………………………………………………………………………
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SACE 2 BIOLOGY Essentials WORKBOOK
transcription
……………………………………………………………………………………………
translation
……………………………………………………………………………………………
tRNA
……………………………………………………………………………………………
2. To help you identify differences between DNA, mRNA, and tRNA, complete the following statements
by writing the appropriate nucleic acid(s) after each one.
a. is single stranded
……………..
M
b.
has a double helical structure
……………..
c.
is only found in the cytoplasm
……………..
d.
is found primarily in the nucleus of a cell
……………..
e.
contains the base thymine
……………..
f.
contains the base uracil
……………..
g.
is involved in the process of replication
……………..
h.
carries amino acids to the ribosomes
……………..
i
has triplets of bases called codons
……………..
j
is found in both the nucleus and cytoplasm
……………..
k
has three bases which comprise the anticodon
……………..
3. Explain the role of the following in the process of protein synthesis:
DNA
………………………………………………………………………………………………………..
…………………………………………………………………………………………………………………………...
mRNA
………………………………………………………………………………………………………..
…………………………………………………………………………………………………………………………...
tRNA
………………………………………………………………………………………………………..
…………………………………………………………………………………………………………………………...
amino acids ………………………………………………………………………………………………………..
…………………………………………………………………………………………………………………………...
ribosomes
………………………………………………………………………………………………………..
…………………………………………………………………………………………………………………………...
mitochondria……………………………………………………………………………………………………….
…………………………………………………………………………………………………………………………..
4. Explain the difference between:
a) transcription and translation
………………………………………………………………………………………………………………………
………………………………………………………………………………………………………………………
b) a codon and an anti-codon
………………………………………………………………………………………………………………………
………………………………………………………………………………………………………………………
© Crierie A. and Greig D. 2004 All rights are reserved, copying is prohibited by law.
13
Worksheet 3 DNA AND PROTEIN SYNTHESIS
5. Use the diagram below, which shows a summary of the process of protein synthesis,to write the
names and roles of the structures labelled:
NUCLEUS
CYTOPLASM
A
T
C
G
C
TA
E
G
CG
C
T
A
U
T
C
C
A
A
C
G
A
C
U
UA
T
D
J
U
A
T
A
G
G
C
I
G
C
C
U
C
U
C
C
B
C
T A
F
U
G
C
U
A
T
Leucine
C
Serine
M
T A
L
CG
T
A
A
A
U
U
C
A
U
U
A
A
G
U
H
K
G
A
…………………………………………………………………………………………………………………
B
…………………………………………………………………………………………………………………
C
…………………………………………………………………………………………………………………
D
…………………………………………………………………………………………………………………
E
…………………………………………………………………………………………………………………
F
…………………………………………………………………………………………………………………
G
…………………………………………………………………………………………………………………
H
…………………………………………………………………………………………………………………
I
…………………………………………………………………………………………………………………
J
…………………………………………………………………………………………………………………
K
…………………………………………………………………………………………………………………
L
…………………………………………………………………………………………………………………
M
…………………………………………………………………………………………………………………
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14
SACE 2 BIOLOGY Essentials WORKBOOK
6. The table below shows which codons carry the information for each amino acid.
M
UUU
UUC
UUA
UUG
phe
phe
leu
leu
UCU
UCC
UCA
UCG
ser
ser
ser
ser
UAU
UAC
UAA
UAG
tyr
tyr
stop
stop
UGU
UGC
UGA
UGG
cys
cys
stop
trp
CUU
CUC
CUA
CUG
leu
leu
leu
leu
CCU
CCC
CCA
CCG
pro
pro
pro
pro
CAU
CAC
CAA
CAG
his
his
gln
gln
CGU
CGC
CGA
CGG
arg
arg
arg
arg
AUU
AUC
AUA
AUG
ile
ile
ile
start/met
ACU
ACC
ACA
ACG
thr
thr
thr
thr
AAU
AAC
AAA
AAG
asn
asn
lys
lys
AGU
AGC
AGA
AGG
ser
ser
arg
arg
GUU
GUC
GUA
GUG
val
val
val
val
GCU
GCC
GCA
GCG
ala
ala
ala
ala
GAU
GAC
GAA
GAG
asp
asp
glu
glu
GGU
GGC
GGA
GGG
gly
gly
gly
gly
The table below shows the names of the amino acids together with the abbreviations used in the table
above.
ala =
arg =
asn =
asp =
cys =
gln =
glu =
alanine
arginine
asparagine
aspartic acid
cysteine
glutamine
glutamic acid
gly =
his =
ile =
leu =
lys =
met =
phe =
glycine
histidine
isoleucine
leucine
lysine
methionine
phenylalanine
pro =
ser =
thr =
trp =
tyr =
val =
proline
serine
threonine
tryptophan
tyrosine
valine
Now, use the table of the genetic code and names of the amino acids given to help you complete the
following table.
DNA base triplets
AGA
________
________
________
mRNA codons
________
CGG
________
________
tRNA anti-codons
________
________
CUG
________
amino acid coded for
________
________
________
methionine
© Crierie A. and Greig D. 2004 All rights are reserved, copying is prohibited by law.
Worksheet 4 STRUCTURE AND FUNCTION OF PROTEINS
Worksheet 4
15
Structure and function of protein molecules
Protein molecules are large polymers made up of about 20 common building blocks called amino acids
linked together. Organisms typically, have thousands of these molecules. Humans are thought to have
between 50,000-100,000 different proteins, each one with a unique three-dimensional structure that is
critical for its particular function. Proteins can be placed into 2 main groups, fibrous or structural
proteins, and globular proteins.
Protein structure can be studied at four levels
x Primary structure - the sequence of amino acids linked by peptide bonds. Each protein is characterised
by its own unique number, type and sequence of amino acids. Typically proteins are made up of
hundreds to thousands of amino acids, haemoglobin, a transport protein, is some 400 times bigger in
size than a glucose molecule.
x Secondary structure - the coiling or folding of the polypeptide chain.
x Tertiary structure - the three-dimensional structure, which is important for binding.
x Quaternary structure - applies to those proteins with more than one polypeptide strand.
It is the tertiary structure of each specific protein that determines its specific function. If the delicate threedimensional shape of a protein is altered, it usually follows that the function of that protein is also
inhibited, this is called denaturation. The diagram below gives a diagrammatic representation of the
different levels of structure in a molecule of haemoglobin which is a protein found in blood.
Polypeptide
chain
ala
gly
leu
val
Heme
lys
PRIMARY
STRUCTURE
SECONDARY
STRUCTURE
TERTIARY
STRUCTURE
Polypeptide
chain
QUATERNARY
STRUCTURE
The structural proteins are more fibrous in nature and tend to have repeating units of amino acid
sequences, whereas the globular proteins each have their own unique sequences giving them their
particular shape that is so vital for their function.
Types of proteins.
Proteins can be placed into groups depending on their particular roles in the organism.
Structural
Examples include those that make up ligaments and tendons, while others assist in movement, for
example muscle proteins. Keratin is an important structural protein found in organisms, it makes up the
outer layer of skin, and is the main component of hair, nails, wool, beaks and feathers. Proteins
embedded in the cell membrane are vital for the efficient functioning of cells. Some have roles in acting as
channel proteins allowing certain molecules to enter or leave cells, but not others. Other proteins act as
receptor proteins that can bind to chemicals like hormones, and thus bring about a particular response.
Defence
Specific protein molecules, called antibodies, are released from white blood cells and have a role in the
inactivation and destruction of foreign antigen molecules that may invade our tissues. The unique shape
of the protein antibody means that the action of each antibody is specific for a particular antigen; one
particular antibody can only bind with and inactivate one particular antigen.
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SACE 2 BIOLOGY Essentials WORKBOOK
Communication
Certain molecules, including some hormones, bring about their specific action by binding to other
molecules. When the hormone insulin binds to receptor proteins in the cell membrane, the cell membrane
increase its permeability to glucose and the cell takes up more glucose to store as glycogen. The diagram
below represents the binding of a hormone to a surface receptor.
Hormone messenger molecule
Receptor molecule embedded
into the bi-lipid layer of
cell membrane
M
Lipid bi-layer
Binding leads to activation
Transport
Haemoglobin is a protein molecule found inside human red blood cells. It has a specific role in the
transport of oxygen molecules to the tissues of the body. The particular shape of the molecule makes it
ideal for the reversible binding that occurs with oxygen.
The control of metabolic reactions.
All reactions inside cells need specific enzyme molecules to ensure that they proceed. Enzymes are
protein molecules with a specific shape that is critical for the binding of the reactant or substrate
molecules. The three dimensional shape of the protein gives rise to an active site on the enzyme where an
induced fit binding occurs.
1. Write a concise statement to explain each of the following terms:
antibody
……………………………………………………………………………………………
antigen
……………………………………………………………………………………………
complementary strand ………………………………………………………………………………………..
denature
……………………………………………………………………………………………
enzyme
……………………………………………………………………………………………
haemoglobin
……………………………………………………………………………………………
hormone
……………………………………………………………………………………………
insulin
……………………………………………………………………………………………
polypeptide
……………………………………………………………………………………………
protein
……………………………………………………………………………………………
surface receptor
……………………………………………………………………………………………
© Crierie A. and Greig D. 2004 All rights are reserved, copying is prohibited by law.
Worksheet 4 STRUCTURE AND FUNCTION OF PROTEINS
17
2. Explain how it is possible for a cell to make hundreds of possible proteins out of only 20 amino acids.
Compare this to making words from the letters of the alphabet.
………………………………………………………………………………………………………………………
………………………………………………………………………………………………………………………
………………………………………………………………………………………………………………………
………………………………………………………………………………………………………………………
3. Egg white consists of a runny, clear protein called albumin. Upon heating, it turns white and changes
its consistency. Suggest why the protein does not change back to its original form upon cooling.
………………………………………………………………………………………………………………………
………………………………………………………………………………………………………………………
4. Suggest how changing the pH of the cellular environment may alter the function of enzymes.
………………………………………………………………………………………………………………………
………………………………………………………………………………………………………………………
………………………………………………………………………………………………………………………
………………………………………………………………………………………………………………………
5. Describe four functions of proteins in cells.
………………………………………………………………………………………………………………………
………………………………………………………………………………………………………………………
………………………………………………………………………………………………………………………
………………………………………………………………………………………………………………………
6. Antigens are foreign substances, for example toxins or surface molecules on the bacteria and viruses,
that stimulate the production of special proteins called antibodies. Suggest how the complementary
shape of the protein antibody may be important in destroying such invaders.
………………………………………………………………………………………………………………………
………………………………………………………………………………………………………………………
7. Explain the importance of the shape of an enzyme in catalysing cell reactions. Use a diagram to assist
with your explanation.
………………………………………………………………………………………………………………………
………………………………………………………………………………………………………………………
8. Adrenalin is a protein hormone that binds to surface receptors in liver cells. This binding brings about
the conversion of glycogen into glucose. Explain why adrenalin only affects some cells like liver cells
and not all cells in the organism.
………………………………………………………………………………………………………………………
………………………………………………………………………………………………………………………
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18
SACE 2 BIOLOGY Essentials WORKBOOK
Worksheet 5
The importance of polysaccharides and lipids
Polysaccharides and lipids are both important groups of macromolecules in cells. Polysaccharides are
polymers made up of repeating simple sugar units whereas most lipids are made up of fatty acids and
glycerol.
Polysaccharides
M
Polysaccharides are important as both structural molecules and as energy reserves. Important examples
of these include:
Cellulose: - a tough fibrous material that makes up the cell walls of plant cells. It could contain as many
as 10 thousand glucose molecules linked together. The diagram below shows the structure of a typical
polysaccharide, in this case cellulose, which is made up of repeating simple monomer units of glucose.
Cellulose can not be digested by humans but is important in the diet as fibre or roughage.
Cellulose
fibrils
Long chain of simple sugars
Starch: - another big polymer, formed by linking many glucose molecules together, is a store of energy
for the plant and can be broken down when required to release sugar for respiration.
Chitin: - a structural polysaccharide that is the main component of the exoskeleton of insects and
crustaceans.
Glycogen: - this is the molecule that animals use to store their excess sugar. It is a large polymer of
glucose units linked together. Glycogen is stored primarily in the liver and muscle tissue.
Lipids
Lipids vary from simple fats or oils and waxes up to more complex phospholipids and steroids.
Phospholipids are important lipids that form the bi-layer in the cell membrane.
Fats and oils
These can have structural significance as with the waxy cuticle on the leaves of plants that help to reduce
water loss, or can be used as a store of energy. Other molecules, like protein and carbohydrates, can be
converted into fats for storage in the tissues. Fats yield twice as much energy per gram when compared to
carbohydrate stores. Fats are also found surrounding important organs in the body of many organisms
for protection and insulation. An examination of many animals from cold arctic or Antarctic regions
would reveal the presence of significant layers of fat acting as insulation from the cold.
The cell membrane consists of two layers of lipids sandwiched together and embedded into this layer are
important protein molecules.
© Crierie A. and Greig D. 2004 All rights are reserved, copying is prohibited by law.