USABO UPDATED COMPREHENSIVE QUESTIONS
AND ANSWERS SET A+
✔✔Nucleotide - ✔✔The basic building block of nucleic acids, such as DNA and RNA. It
is an organic compound made up of nitrogenous base, a sugar, and a phosphate group.
✔✔cis-unsaturated fatty acid - ✔✔A cis configuration means that adjacent hydrogen
atoms are on the same side of the double bond. The rigidity of the double bond freezes
its conformation and, in the case of the cis isomer, causes the chain to bend and
restricts the conformational freedom of the fatty acid. The more double bonds the chain
has in the cis configuration, the less flexibility it has. When a chain has many cis bonds,
it becomes quite curved in its most accessible conformations. For example, oleic acid,
with one double bond, has a "kink" in it, whereas linoleic acid, with two double bonds,
has a more pronounced bend. Alpha-linolenic acid, with three double bonds, favors a
hooked shape. The effect of this is that, in restricted environments, such as when fatty
acids are part of a phospholipid in a lipid bilayer, or triglycerides in lipid droplets, cis
bonds limit the ability of fatty acids to be closely packed, and therefore could affect the
melting temperature of the membrane or of the fat.
✔✔Fatty Acid - ✔✔A carboxylic acid with a long unbranched aliphatic tail (chain), which
is either saturated or unsaturated. Most naturally occurring fatty acids have a chain of
an even number of carbon atoms, from 4 to 28. Fatty acids are usually derived from
triglycerides or phospholipids. When they are not attached to other molecules, they are
known as "free" fatty acids. Fatty acids are important sources of fuel because,
metabolized, they yield large quantities of ATP. Many cell types can use either glucose
or fatty acids for this purpose. In particular, heart and skeletal muscle prefer fatty acids.
The brain cannot use fatty acids as a source of fuel; it relies on glucose or ketone
bodies.
✔✔Saturated fatty acids - ✔✔Saturated fatty acids are long-chain carboxylic acids that
usually have between 12 and 24 carbon atoms and have no double bonds. Thus,
saturated fatty acids are saturated with hydrogen (since double bonds reduce the
number of hydrogens on each carbon). Because saturated fatty acids have only single
,bonds, each carbon atom within the chain has 2 hydrogen atoms (except for the omega
carbon at the end that has 3 hydrogens).
✔✔Cholesterol - ✔✔A waxy steroid of fat that is produced in the liver or intestines. It is
used to produce hormones and cell membranes and is transported in the blood plasma
of all mammals. It is an essential structural component of mammalian cell membranes
and is required to establish proper membrane permeability and fluidity.It causes areas
of rigidity in the membrane due to the interaction of its four fused ring sections with the
hydrophobic tails of surrounding lipids.In addition, cholesterol is an important
component for the manufacture of bile acids, steroid hormones, and vitamin D.
Cholesterol is the principal sterol synthesized by animals; however, small quantities can
be synthesized in other eukaryotes such as plants and fungi. It is almost completely
absent among prokaryotes including bacteria. Although cholesterol is important and
necessary for mammals, high levels of cholesterol in the blood can damage arteries and
are potentially linked to diseases such as those associated with the cardiovascular
system (heart disease).
✔✔Integral membrane proteins - ✔✔Proteins which span the width of the cell
membrane, protruding on the apical and basal surface.
✔✔Peripheral membrane proteins - ✔✔Proteins found in the cell membrane which
attached to only one side of the membrane.
✔✔Multipass integral membrane protein - ✔✔An integral protein which has a
polypeptide change which loops back across the membrane several times.
✔✔Spectrin - ✔✔A membrane protein that cross links actin filaments.
✔✔Anchoring Junction - ✔✔Junctions present in many types of animal tissue which
serve to hold the constituentcells to each other and to the surrounding extra cellular
matrix. They all have a common general structure consisting of transmembrane protein
molecules known as cadhedrins.
✔✔Cadherin - ✔✔Cadherins (named for "calcium-dependent adhesion") are a class of
type-1 transmembrane proteins. They play important roles in cell adhesion, ensuring
that cells within tissues are bound together. They are dependent on calcium (Ca2+) ions
to function, hence their name. The extra cellular domains on cadherins interact with
their counterparts in other cell membranes and their intracellular domains interact
intracellular proteins. The intracellular proteins are then bound to cytoskeleton
intermediate filaments known as keratin.
✔✔Adherens Junctions - ✔✔These junctions function in the same way as anchoring
junctions, linking intercellular cytoskeletons using cadherin. Unlike the anchoring
junctions these junctions use the actin filaments not the intermediate filaments to secure
the cells.
,✔✔Plasmodesmata - ✔✔Membrane lined gap junctions which cross cell walls in plants.
✔✔Connexon - ✔✔A multisubunit protein which holds gap junctions together in animal
cells.
✔✔Glycophorin - ✔✔Negatively charged membrane glycoprotein which help to prevent
red blood cells from sticking together through the actions of sialic acid sugar which is
attached to it's extracellular domain .
✔✔N-CAMS/Neural Cell Adehesion Molecules - ✔✔Membrane glycoproteins with an
extracellular region made up of several domains. They are involved in the formation of
intercellular junctions in neural tissue and unlike cadherins are not calcium dependant.
As with cadherins they have sialic acid sugar components giving the cell membrane a
negative charge discouragin inter cell adhesion.
✔✔Sialic Acid - ✔✔A generic term for the N- or O-substituted derivatives of neuraminic
acid, a monosaccharide with a nine-carbon backbone. It is the sugar present on
cadherins and N-CAMS which gives them their negative charge. It is also the name for
the most common member of this group, N-acetylneuraminic acid (Neu5Ac or NANA).
Sialic acids are found widely distributed in animal tissues and to a lesser extent in other
species ranging from plants and fungi to yeasts and bacteria, mostly in glycoproteins
and gangliosides. The amino group generally bears either an acetyl or glycolyl group
but other modifications have been described. The hydroxyl substituents may vary
considerably: acetyl, lactyl, methyl, sulfate, and phosphate groups have been found.
✔✔Passive diffusion - ✔✔This route of diffusion requires no assistance from membrane
proteins or other sources. Non polar molecules such as oxygen and steroids pass easily
through the lipid bilayer of the cell membrane as they are lipid soluble. Some small polar
molecules, such as water, can also pass through the membrane via this route.
✔✔Carrier Protein - ✔✔A membrane protein, involved in passive and active transport,
that binds to a solute molecule or ion and releases it on the other side of the membrane.
An example of this is the glucose carrier protein in mammalian cells which responds
only to glucose and not other sugars and moves glucose down a concentration gradient
from the outside to the inside of the cell.
✔✔Facilitated diffusion - ✔✔Also known as facilitated transport or passive-mediated
transport) is a process of passive transport, facilitated by integral proteins. Facilitated
diffusion is the spontaneous passage of molecules or ions across a biological
membrane passing through specific transmembrane integral proteins in response to
messages received or changes in extracellular conditions. It works along the
concentration gradient and does not require any energy.
, ✔✔Active transport - ✔✔This form of transport is the movement of a substance against
its concentration gradient (from low to high concentration). In all cells, this is usually
concerned with accumulating high concentrations of molecules that the cell needs, such
as ions, glucose, and amino acids. If the process uses chemical energy, such as from
adenosine triphosphate (ATP), it is termed primary active transport. Secondary active
transport involves the use of an electrochemical gradient. Active transport uses energy,
unlike passive transport, which does not use any type of energy. Active transport is a
good example of a process for which cells require energy. Examples of active transport
include the uptake of glucose in the intestines in humans and the uptake of mineral ions
into root hair cells of plants.
✔✔Ficks Law - ✔✔These laws of diffusion describe diffusion and can be used to solve
for the diffusion coefficient, D. They were derived by Adolf Fick in the year 1855.The
equation relates the difference (Ch-Cl) between the higher, Ch, and the lower Cl,
concentrations of the substance, the area (A) and the thickness (x)of the membrane and
a constant (D), called the diffusion coefficient, the value of which depends on the nature
of the diffusing substance (e.g polarity, size, temperature etc).
✔✔Membrane potential - ✔✔Also known as transmembrane potential this is the
difference in voltage (also called electrical potential) between the interior and exterior of
a cell. The membrane potential arises from the interactions of ion channels and ion
pumps embedded in the membrane, which produce different concentrations of
electrically charged ions on the intracellular and extracellular sides of the membrane.
This enhances the passage of positive ions and impedes the entry of negative ions via
the cell membrane.
✔✔Sodium Pump - ✔✔This pump is involved in active transport and is responsible for
cells containing relatively high concentrations of potassium ions but low concentrations
of sodium ions. It moves these two ions in opposite directions across the plasma
membrane. This was investigated by following the passage of radioactively labeled ions
across the plasma membrane of certain cells. It was found that the concentrations of
sodium and potassium ions on the two other sides of the membrane are interdependent,
suggesting that the same carrier transports both ions. It is now known that the carrier is
an ATP-ase and that it pumps three sodium ions out of the cell for every two potassium
ions pumped in.
✔✔Primary active transport - ✔✔This type of transport is also called direct active
transport, directly uses energy to transport molecules across a membrane.
Most of the enzymes that perform this type of transport are transmembrane ATPases. A
primary ATPase universal to all cellular life is the sodium-potassium pump, which helps
to maintain the cell potential. Other sources of energy for Primary active transport are
redox energy and photon energy (light). An example of primary active transport using
Redox energy is the mitochondrial electron transport chain that uses the reduction
energy of NADH to move protons across the inner mitochondrial membrane against
their concentration gradient. An example of primary active transport using light energy
are the proteins involved in photosynthesis that use the energy of photons to create a
AND ANSWERS SET A+
✔✔Nucleotide - ✔✔The basic building block of nucleic acids, such as DNA and RNA. It
is an organic compound made up of nitrogenous base, a sugar, and a phosphate group.
✔✔cis-unsaturated fatty acid - ✔✔A cis configuration means that adjacent hydrogen
atoms are on the same side of the double bond. The rigidity of the double bond freezes
its conformation and, in the case of the cis isomer, causes the chain to bend and
restricts the conformational freedom of the fatty acid. The more double bonds the chain
has in the cis configuration, the less flexibility it has. When a chain has many cis bonds,
it becomes quite curved in its most accessible conformations. For example, oleic acid,
with one double bond, has a "kink" in it, whereas linoleic acid, with two double bonds,
has a more pronounced bend. Alpha-linolenic acid, with three double bonds, favors a
hooked shape. The effect of this is that, in restricted environments, such as when fatty
acids are part of a phospholipid in a lipid bilayer, or triglycerides in lipid droplets, cis
bonds limit the ability of fatty acids to be closely packed, and therefore could affect the
melting temperature of the membrane or of the fat.
✔✔Fatty Acid - ✔✔A carboxylic acid with a long unbranched aliphatic tail (chain), which
is either saturated or unsaturated. Most naturally occurring fatty acids have a chain of
an even number of carbon atoms, from 4 to 28. Fatty acids are usually derived from
triglycerides or phospholipids. When they are not attached to other molecules, they are
known as "free" fatty acids. Fatty acids are important sources of fuel because,
metabolized, they yield large quantities of ATP. Many cell types can use either glucose
or fatty acids for this purpose. In particular, heart and skeletal muscle prefer fatty acids.
The brain cannot use fatty acids as a source of fuel; it relies on glucose or ketone
bodies.
✔✔Saturated fatty acids - ✔✔Saturated fatty acids are long-chain carboxylic acids that
usually have between 12 and 24 carbon atoms and have no double bonds. Thus,
saturated fatty acids are saturated with hydrogen (since double bonds reduce the
number of hydrogens on each carbon). Because saturated fatty acids have only single
,bonds, each carbon atom within the chain has 2 hydrogen atoms (except for the omega
carbon at the end that has 3 hydrogens).
✔✔Cholesterol - ✔✔A waxy steroid of fat that is produced in the liver or intestines. It is
used to produce hormones and cell membranes and is transported in the blood plasma
of all mammals. It is an essential structural component of mammalian cell membranes
and is required to establish proper membrane permeability and fluidity.It causes areas
of rigidity in the membrane due to the interaction of its four fused ring sections with the
hydrophobic tails of surrounding lipids.In addition, cholesterol is an important
component for the manufacture of bile acids, steroid hormones, and vitamin D.
Cholesterol is the principal sterol synthesized by animals; however, small quantities can
be synthesized in other eukaryotes such as plants and fungi. It is almost completely
absent among prokaryotes including bacteria. Although cholesterol is important and
necessary for mammals, high levels of cholesterol in the blood can damage arteries and
are potentially linked to diseases such as those associated with the cardiovascular
system (heart disease).
✔✔Integral membrane proteins - ✔✔Proteins which span the width of the cell
membrane, protruding on the apical and basal surface.
✔✔Peripheral membrane proteins - ✔✔Proteins found in the cell membrane which
attached to only one side of the membrane.
✔✔Multipass integral membrane protein - ✔✔An integral protein which has a
polypeptide change which loops back across the membrane several times.
✔✔Spectrin - ✔✔A membrane protein that cross links actin filaments.
✔✔Anchoring Junction - ✔✔Junctions present in many types of animal tissue which
serve to hold the constituentcells to each other and to the surrounding extra cellular
matrix. They all have a common general structure consisting of transmembrane protein
molecules known as cadhedrins.
✔✔Cadherin - ✔✔Cadherins (named for "calcium-dependent adhesion") are a class of
type-1 transmembrane proteins. They play important roles in cell adhesion, ensuring
that cells within tissues are bound together. They are dependent on calcium (Ca2+) ions
to function, hence their name. The extra cellular domains on cadherins interact with
their counterparts in other cell membranes and their intracellular domains interact
intracellular proteins. The intracellular proteins are then bound to cytoskeleton
intermediate filaments known as keratin.
✔✔Adherens Junctions - ✔✔These junctions function in the same way as anchoring
junctions, linking intercellular cytoskeletons using cadherin. Unlike the anchoring
junctions these junctions use the actin filaments not the intermediate filaments to secure
the cells.
,✔✔Plasmodesmata - ✔✔Membrane lined gap junctions which cross cell walls in plants.
✔✔Connexon - ✔✔A multisubunit protein which holds gap junctions together in animal
cells.
✔✔Glycophorin - ✔✔Negatively charged membrane glycoprotein which help to prevent
red blood cells from sticking together through the actions of sialic acid sugar which is
attached to it's extracellular domain .
✔✔N-CAMS/Neural Cell Adehesion Molecules - ✔✔Membrane glycoproteins with an
extracellular region made up of several domains. They are involved in the formation of
intercellular junctions in neural tissue and unlike cadherins are not calcium dependant.
As with cadherins they have sialic acid sugar components giving the cell membrane a
negative charge discouragin inter cell adhesion.
✔✔Sialic Acid - ✔✔A generic term for the N- or O-substituted derivatives of neuraminic
acid, a monosaccharide with a nine-carbon backbone. It is the sugar present on
cadherins and N-CAMS which gives them their negative charge. It is also the name for
the most common member of this group, N-acetylneuraminic acid (Neu5Ac or NANA).
Sialic acids are found widely distributed in animal tissues and to a lesser extent in other
species ranging from plants and fungi to yeasts and bacteria, mostly in glycoproteins
and gangliosides. The amino group generally bears either an acetyl or glycolyl group
but other modifications have been described. The hydroxyl substituents may vary
considerably: acetyl, lactyl, methyl, sulfate, and phosphate groups have been found.
✔✔Passive diffusion - ✔✔This route of diffusion requires no assistance from membrane
proteins or other sources. Non polar molecules such as oxygen and steroids pass easily
through the lipid bilayer of the cell membrane as they are lipid soluble. Some small polar
molecules, such as water, can also pass through the membrane via this route.
✔✔Carrier Protein - ✔✔A membrane protein, involved in passive and active transport,
that binds to a solute molecule or ion and releases it on the other side of the membrane.
An example of this is the glucose carrier protein in mammalian cells which responds
only to glucose and not other sugars and moves glucose down a concentration gradient
from the outside to the inside of the cell.
✔✔Facilitated diffusion - ✔✔Also known as facilitated transport or passive-mediated
transport) is a process of passive transport, facilitated by integral proteins. Facilitated
diffusion is the spontaneous passage of molecules or ions across a biological
membrane passing through specific transmembrane integral proteins in response to
messages received or changes in extracellular conditions. It works along the
concentration gradient and does not require any energy.
, ✔✔Active transport - ✔✔This form of transport is the movement of a substance against
its concentration gradient (from low to high concentration). In all cells, this is usually
concerned with accumulating high concentrations of molecules that the cell needs, such
as ions, glucose, and amino acids. If the process uses chemical energy, such as from
adenosine triphosphate (ATP), it is termed primary active transport. Secondary active
transport involves the use of an electrochemical gradient. Active transport uses energy,
unlike passive transport, which does not use any type of energy. Active transport is a
good example of a process for which cells require energy. Examples of active transport
include the uptake of glucose in the intestines in humans and the uptake of mineral ions
into root hair cells of plants.
✔✔Ficks Law - ✔✔These laws of diffusion describe diffusion and can be used to solve
for the diffusion coefficient, D. They were derived by Adolf Fick in the year 1855.The
equation relates the difference (Ch-Cl) between the higher, Ch, and the lower Cl,
concentrations of the substance, the area (A) and the thickness (x)of the membrane and
a constant (D), called the diffusion coefficient, the value of which depends on the nature
of the diffusing substance (e.g polarity, size, temperature etc).
✔✔Membrane potential - ✔✔Also known as transmembrane potential this is the
difference in voltage (also called electrical potential) between the interior and exterior of
a cell. The membrane potential arises from the interactions of ion channels and ion
pumps embedded in the membrane, which produce different concentrations of
electrically charged ions on the intracellular and extracellular sides of the membrane.
This enhances the passage of positive ions and impedes the entry of negative ions via
the cell membrane.
✔✔Sodium Pump - ✔✔This pump is involved in active transport and is responsible for
cells containing relatively high concentrations of potassium ions but low concentrations
of sodium ions. It moves these two ions in opposite directions across the plasma
membrane. This was investigated by following the passage of radioactively labeled ions
across the plasma membrane of certain cells. It was found that the concentrations of
sodium and potassium ions on the two other sides of the membrane are interdependent,
suggesting that the same carrier transports both ions. It is now known that the carrier is
an ATP-ase and that it pumps three sodium ions out of the cell for every two potassium
ions pumped in.
✔✔Primary active transport - ✔✔This type of transport is also called direct active
transport, directly uses energy to transport molecules across a membrane.
Most of the enzymes that perform this type of transport are transmembrane ATPases. A
primary ATPase universal to all cellular life is the sodium-potassium pump, which helps
to maintain the cell potential. Other sources of energy for Primary active transport are
redox energy and photon energy (light). An example of primary active transport using
Redox energy is the mitochondrial electron transport chain that uses the reduction
energy of NADH to move protons across the inner mitochondrial membrane against
their concentration gradient. An example of primary active transport using light energy
are the proteins involved in photosynthesis that use the energy of photons to create a
