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Content covered in this material for the Biology Keystone Test
1. Describe the unique properties of water and how these properties
support life on Earth(e.g. freezing point, high specific heat,
cohesion).
2. Explain how carbon is uniquely suited to form biological
macromolecules.
3. Describe how biological macromolecules form from monomers.
4. Compare the structure and function of carbohydrates, lipids,
proteins, and nucleic acids in organisms.
5. Describe the role of an enzyme as a catalyst in regulating a specific
biochemical reation.
6. Explain how factors such as pH, temperature, and concentration
levels can affect enzyme function.
Use a sheet of paper to cover the answers to the questions. Try to answer the
questions to the best of your knowledge. Check the answer and be sure to read the
background information that follows.
WATER AND ITS PROPERTIES
QUESTION 1.
1. Which statement best describes an effect of the
low density of frozen water in a lake?
A. When water freezes, it contracts, decreasing
the water level in a lake.
B. Water in a lake freezes from the bottom up,
killing most aquatic organisms.
C. When water in a lake freezes, it floats, providing
insulation for organisms below.
D. Water removes thermal energy from the land
around a lake, causing the lake to freeze.
Answer C
Most liquids shrink when cooled down, but water is an exception. Water expands
when it freezes. This is a result of hydrogen bonds between water molecules.
The hydrogen bonds are responsible for other unusual properties of water,
including its high boiling point, high heat of vaporization, cohesion, and adhesion.
The hydrogen bond is a strong intermolecular force of attraction
between the oxygen of one water molecule with the hydrogen of another water molecule.
In water's liquid form, as seen below, water molecules form extensive hydrogen
bonds. Notice that there is not a regular structure to water. The large heat of
vaporization of water is largely due to the need to break all of the hydrogen bonds
in order to produce water vapor.
Ice forms a hexagonal structure. In ice, the structure is rigid and molecules are held
in place by a vast network of hydrogen bonds. Because of the open nature of the
hexagonal lattice, ice is less dense than water.
ICE
The hydrogen bonds of water cause cohesion: water attracted to water!
Cohesion causes water to form drops and causes the phenomenon called surface
tension.
The cohesive forces between molecules down into a liquid are shared with all
neighboring atoms. Those on the surface have no neighboring atoms above, and
exhibit stronger attractive forces upon their nearest neighbors on the surface. This
enhancement of the intermolecular attractive forces at the surface is called surface
tension.
Adhesion: Water is attracted to other substances.
Because water has adhesive properties, things get wet. Water is attracted to cloth,
organic tissues, glass, paper, etc.
Adhesion powers capillary action, a process where water can move up the sides of
thin tubes, such as the stem or root of a plant.
Plants put down roots into the soil which are capable of carrying water from the
soil up into the plant. Water, which contains dissolved nutrients, gets inside the
roots and starts climbing up the plant tissue.
Water is a polar molecule. The oxygen in the water has a partial negative charge
and the hydrogen side has a partial positive side, making it a polar molecule. This
allows water to be attracted to many other substances which are also polar and
allows it to dissolve many polar substances.
Water cannot dissolve nonpolar substances, such as oil!
This is important to every living thing on earth. It means that wherever water goes,
either through the air, the ground, or through our bodies, it takes along valuable
chemicals, minerals, and nutrients.
Water has a high specific heat. This means it absorbs a lot of heat before it begins
to get hot.
The high specific heat capacity of water has a great deal to do with regulating
extremes in the environment. For instance, the fish in the pond is indeed happy
because the heat capacity of the water in his pond above means the temperature of
the water will stay relatively the same from day to night.
Water freezes at 0ºC (32ºF) and boils at 100ºC (212 ºF).
When water freezes, this is an exothermic process. Bonds are being formed to
form the ice. This releases heat energy, which is exothermic.
Carbon and macromolecules
QUESTION 2
2. Which statement correctly describes how carbon’s
ability to form four bonds makes it uniquely suited
to form macromolecules?
A. It forms short, simple carbon chains.
B. It forms large, complex, diverse molecules.
C. It forms covalent bonds with other carbon
atoms.
D. It forms covalent bonds that can exist in a
single plane.
Answer B
QUESTION 3
3. Use the diagram below to answer the question.
Chemical Reaction
HO-1- 2 -3- H + HO- 4- H
HO-1- 2- 3-4- H
+
H2 O
The diagram shows a reaction that forms a polymer
from two monomers. What is this type of reaction
called?
A. glycolysis
B. hydrolysis
C. photosynthesis
D. dehydration synthesis
Answer D
Your body is nearly 70% water and the rest of matter in your body is made of
organic compounds.
An organic compound is a compound that contains a carbon atom. The carbon
atoms are usually covalently bonded to other atoms such as hydrogen and oxygen,
forming large molecules called macromolecules.
Carbon can form a wide variety of molecules!
Carbon is a unique element that has four valence (outer energy level) electrons that
can be shared with other carbon atoms or atoms other than carbon to form covalent
bonds . It can form single, double, or triple bonds. Carbon also can form long
chains and ring structures.
single
H
|
H--C--H
|
H
double
HH
||
H--C==C--H
||
HH
triple
H
|
C
|||
C
|
H
Small organic molecules are the basic stuff of life. Scientists call them monomers.
Mono means one. These monomers actually make up building blocks for bigger
things. You can think of them as one brick that makes up a brick wall. When
monomers (small molecules) are joined together, they form larger molecules called
polymers. Poly means many. Think of the polymers as that brick wall. And when
polymers are joined together, they form “giant” molecules called macromolecules.
Macro means big. You can think of these macromolecules as the building that is
made up of those brick walls.
There are 4 main groups of macromolecules:
Carbohydrates
Proteins
Lipids
Nucleic acids
CARBOHYDRATES
These macromolecules are made of carbon, hydrogen, and oxygen in a ratio of
1:2:1.
Function of carbohydrates:
1. -energy storage in plants and animals (sugars are for Energy)
- There is energy stored in the bonds of carbohydrates
-Cells harvest the energy in chemical bonds
2.- involved as structural components in cells, such as cellulose which is
found in the cell walls of plants.
Monosaccharides
-simple sugars
- glucose C6H12O6
-fructose C6H12O6
- galactose C6H12O6
Notice that all these simple sugars have the same molecular formulas, but they
look different. See the images below.
Disaccharides
- Double sugars when two monosaccharides join together
- Maltose = glucose and glucose
- Sucrose = (Table sugar) glucose and fructose
-
Lactose= ( Milk sugar) galactose and glucose
-Monosaccharides are joined by dehydration synthesis (condensation)
reactions
-Dehydration synthesis is a chemical process by which 2 molecules are joined together to make
a larger, more complex, molecule, with the loss of water
Polysaccharides
- Long repeating chains of monosaccharides
- Animals form the polymer, glycogen, from glucose units
-Plants form the polymers, starch and cellulose from glucose units
Starch is a long (100's) polymer of Glucose molecules, where all the sugars are
oriented in the same direction. Starch is one of the primary sources of calories for
humans.
Cellulose is a long (100's) polymer of Glucose molecules. However the orientation
of the sugars is a little different. In Cellulose, every other sugar molecule is
"upside-down". This small difference in structure makes a big difference in the
way we use this molecule.
Glycogen is another Glucose polymer. Glycogen is a stored energy source, found
in the Liver and muscles of Humans. Glycogen is different from both Starch and
Cellulose in that the Glucose chain is
branched or "forked".
LIPIDS / FATS
- Nonpolar molecules that are not soluble in water, which is polar.
- There are no partial negative or positive charges on lipids, making them
nonpolar.
- Lipids includes:
- fats and oils
- Phospholipids
waxes
steroids (like cholesterol)
Function of lipids
1. Lipids store energy, and provide more energy than carbohydrates or
proteins.
2. Lipids are involved in structural components in cells
Fats and Oils
Fats and oils are made from two kinds of molecules: glycerol and three
fatty acids joined by dehydration synthesis. Since there are three fatty acids
attached, these are known as
triglycerides
Glycerol and fatty acid chains = a triglceride
- Fatty acid chains can be saturated or unsaturated.
- A saturated fatty acid has all single carbon bonds.
-Butter and animal fat are mostly saturated fats and are solids at room
termperture.
- An unsaturated fatty acid has some carbons connected by double covalent
bonds.
- Olive oil, canola oil, fish oils, are mostly unsaturated fats and are liquids at
room temperature.
-Unsaturated oils are healthier than saturated animal fat.
Phospholipids
Phospholipids are a unique group of lipids. In a phospholipid, two fatty acid chains
are bound to a phosphate group. The phosphate group contains lots of oxygen and
is highly polar, and so it is hydrophilic( water fearing). But the fatty acid chains
are nonpolar and so hydrophobic(water loving). This gives phospholipids a sort of
“split personality,” because the phosphate-containing “heads” are strongly attracted
to water, whereas the fatty-acid “tails” are not.
The structure of a phospholipid molecule
Because the hydrophilic heads of phospholipids are attracted to water and the
hydrophobic tails repelled by it, phospholipids will spontaneously arrange
themselves into bilayers in water. A phospholipid bilayer consists of two layers of
phospholipid molecules arranged so that the water-loving heads point outward and
toward the surrounding water, while the tails point inward, away from the water.
Phospholipids are the primary components of the cellular membranes that
surround and hold together all cells. Additionally, most of the organelles within a
cell are either made of or surrounded by membranes that are mostly made of
phospholipids.
Cell Membrane
Cholesterol
This is also a component of the cell membrane and is found between the
phospolipids.
These next three questions are sample essay questions about proteins
Proteins are a major part of every living cell and have many different functions within each cell.
Carbohydrates also perform numerous roles in living things.
4A. Describe the general composition of a protein molecule.
4B. Describe how the structures of proteins differ from the structures of carbohydrates.
4C. Describe how the functions of proteins differ from the functions of carbohydrates
QUESTION 5
5. Carbohydrates and proteins are two types of
macromolecules. Which functional characteristic of
proteins distinguishes them from carbohydrates?
A. large amount of stored information
B. ability to catalyze biochemical reactions
C. efficient storage of usable chemical energy
D. tendency to make cell membranes hydrophobic
Answer B
Proteins
- A macromolecule made up of amino acids
- There are 20 amino acids used as the building block of proteins
- All proteins are made of chains of some or all of these 20 amino
acids. The bond formed between two amino acids by dehydration
synthesis is known as a peptide bond.
- All amino acids have a nitrogen group (NH2) and a COOH group
- Some names of amino acids are lysine, glutamine, methionine
Dehydration synthesis of amino acids
Proteins
- These are polymers made of the amino acids.
- Proteins have many different shapes, depending on their amino acid
sequence.
- The protein polymer can fold into complicated shapes.
- The shape of the protein is very important, because it determines the
protein’s function.
A protein before and after folding
The Many Function of proteins
1. Proteins can be enzymes that promote chemical reactions in the body.
2. Provide structural support
Keratin in hair
Collagen in skin
Fibrin in blood clots
3. Defend against infection
Antibodies
4. Transport
Hemoglobin carries oxygen
5. Regulation
Hormones
QUESTION 6
6.Substance A is converted to substance B in a
metabolic reaction. Which statement best
describes the role of an enzyme during this
reaction?
A. It adjusts the pH of the reaction medium.
B. It provides energy to carry out the reaction.
C. It dissolves substance A in the reaction
medium.
D. It speeds up the reaction without being
consumed.
Answer D
QUESTION 7
7. A scientist observes that, when the pH of the
environment surrounding an enzyme is changed,
the rate the enzyme catalyzes a reaction greatly
decreases. Which statement best describes
how a change in pH can affect an enzyme?
A. A pH change can cause the enzyme to change
its shape.
B. A pH change can remove energy necessary to
activate an enzyme.
C. A pH change can add new molecules to the
structure of the enzyme.
D. A pH change can cause an enzyme to react
with a different substrate
Answer A
Enzymes
-These are proteins that are called catalysts. They speed up chemical
reactions in the body.
- They help maintain homeostasis. Without enzymes, chemical reactions
could not occur fast enough to sustain life.
- The reactions in the body need a certain amount of activation energy to
get them started. The enzymes lower the amount of activation energy needed to
start a reaction.
How enzymes work
-An enzyme acts on a substance called a substrate during a chemical
reaction.
-An enzyme’s shape determines its activity!
- The enzyme has several large folds on its surface. The folds form pockets
called active sites.
- A specific substrate fits into an enzyme’s active site.
- The ezyme and substrate interact, the energy of activation being reduced.
-Products are formed, and the enzyme is free to catalyze another reaction.
Factors affecting enzyme function
-Anything that affects the shape of the enzyme will affect the enzymes activity.
- Temperature changes
- Enzymes operate within a certain temperature range (body temperature).
- Temperatures outside the ideal range of temperatures will affect the
protein bonds, affecting the shape, affecting activity.
- pH changes
- Enzymes operate within a certain pH range. (body pH)
Nucleic acids
DNA and RNA are nucleic acids that are in all of the cells in your body.
These are the information storage devices of cells.
DNA ( Deoxynucleic acid)
- made of 2 strands of nucleotides twisted around each other in a double
helix
- A nucleotide has 3 parts: a 5-carbon sugar, a nitrogen containing base,
and a phosphate group
- The sugar( deoxyribose) and phosphate form the sides of the DNA, like
the sides of a ladder.
- The nitrogen bases are like the rungs of a ladder, being found between
the sides of the DNA.
-
The four bases
Pyrimidines include
Cytosine and thymine
Purines include
Adenine and guanine
Base pairing rules
A purine on one DNA strand bonds with a pyrimidine on the other strand
A-T adenine bonds to thymine
C-G cytosine bonds to guanine
DNA is sometimes called "the blueprint of life" because it contains the code, or
instructions for building and organism and ensuring that organism functions correctly.
Just like a builder uses a blueprint to build a house, DNA is used as the blueprint, or
plans, for the entire organism.
It is the chemical component of chromosomes, which are located in the nucleus of every
cell. Stretches of DNA (or stretches of chromosomes) code for genes.
Gene - a segment of DNA that codes for a protein, which in turn codes for a trait (skin
tone, eye color..etc), a gene is a stretch of DNA.
DNA REPLICATION
Replication is the process where DNA makes a copy of itself. Why does DNA need to
copy? Simple: Cells divide for an organism to grow or reproduce, every new cell needs
a copy of the DNA or instructions to know how to be a cell. DNA replicates right before a
cell divides.
RNA
DNA remains in the nucleus, but in order for it to get its instructions translated into
proteins, it must send its message to the ribosomes, where proteins are made. The
chemical used to carry this message is Messenger RNA
RNA = ribonucleic acid.
RNA is similar to DNA except:
1. has on strand instead of two strands.
2. has uracil instead of thymine
3. has ribose instead of deoxyribose
The instructions for making a protein are transferred
from a gene to an RNA molecule in a process called
transcription.
Cells translate the instructions and put together
amino acids to make proteins.
Transcription - RNA is made from DNA
Translation - Proteins are made from the message on the RNA