Chapter 4
role of active transport processes
active transport requires energy use by the membrane
many enzymes are first synthesized as
inactive proenzymes
main source of energy
glucose
cellular respiration
the pathway by which glucose is broken down to yield its stored energy, is an important example of cell catabolism
Which of the following is an active transport process?
Endocytosis
as molecules diffuse
a state of equilibrium will occur
In the DNA molecule, a sequence of three base pairs forms a(n):
codon.
Glycolysis occurs in what part of the cell?
Cytoplasm
carrier-mediated passive transport
carriers attract and bind to the solute, change shape, and release the solute out the other side of the carrier; carriers are usually reversible depending on the direction of the concentration gradient
Diffusion moves:
down a concentration gradient.
stimuli for gated channels could be
light, chemical, or electrical
anaerobic
no oxygen
Water pressure that develops in a solution as a result of osmosis into that solution is called _____ pressure.
osmotic
exocytosis
process by which large molecules, notably proteins, can leave the cell even though they are too large to move out through the plasma membrane; large molecules are enclosed in membraneous vesicles and then pulled to the plasma membrane by the cytoskeleton, where the contents are released; provides a way for new material to be added to the plasma membrane
active transport processes
require the expenditure of metabolic energy by the cell
metabolism
the set of chemical reactions in a cell
electron transport system
energized electrons are carried by NADH and FADH2 from glycolysis and the citric acid cycle to electron acceptors embedded in the cristae of the mitochondrion
hypotonic
"lower pressure"; cells placed in a hypotonic solution may swell as water flows into them; water always osmoses from the hypotonic solution into the cytosol
Briefly outline each of the major steps of cellular respiration.
Glycolysis is a catabolic pathway that begins with glucose and ends with two molecules of pyruvic acid. Two ATP molecules and NADH are generated in this pathway. The citric acid cycle converts pyruvic acid to acetyl coenzyme A and moves into a sequence of reactions that generate ATP, NADH, FADH2, and carbon dioxide. The electron transport system uses the NADH and FADH2 to transfer energized electrons to a set of special molecules embedded in the cristae of the inner mitochondrial membrane. Additional ATP molecules are formed along with molecules of water.
What are the three catabolic pathways that together make up the processes of cellular respiration?
Glycolysis, citric acid cycle, and the electron transport system make up the process of cellular respiration.
Describe three different active processes that transport substances across a cell membrane. What distinguishes them from passive processes?
Sodium-potassium pump: operates in the plasma membrane by actively transporting sodium ions and potassium ions but in opposite directions. Endocytosis: the plasma membrane "traps" some extracellular material and brings it into the cell. Exocytosis: the process by which large molecules, notably proteins, can leave the cell even though they are too large to move out through the plasma membrane. All of these processes require cell energy.
Which extracts more energy for cell use, the aerobic or anaerobic pathway?
The aerobic pathway extracts more energy.
most enzymes catalyze
a chemical reaction in both directions
hydrases
add water to a molecule without splitting it
transport by vesicles
allows substances to enter or leave the interior of a cell without actually moving through its plasma membrane
catabolism
breaks large molecules into smaller ones; usually releases energy
enzymes that add or remove carbon dioxide
carboxylases or decarboxylases
break down of glucose
catabolism
A chemical that reduces the amount of activation energy needed to start a chemical reaction is a (an):
catalyst.
channel-mediated passive transport
channels are specific; only allow one type of solute to pass through; channels allow membranes to be selectively permeable
role of enzymes
chemical catalysts that reduce the activation energy needed for a reaction; regulate cell metabolism
If oxygen is available, the pyruvic acid molecules formed by glycolysis are prepared to enter the next phase of aerobic cellular respiration called the:
citric acid cycle.
low-energy electrons
coming off the ETS bind to oxygen and rejoin their protons to form water (H2O)
phagocytosis
condition of cell eating; large particles are engulfed by the plasma membrane and enter the cell in vesicles; the vesicles fuse with lysosomes, which digest the particles
enzymes are continually being destroyed and
continually being replaced
isotonic
describes a fluid having the same potential osmotic pressure as cytosol
osmosis
diffusion of water through a selectively permeable membrane; limits diffusion of at least some of the solute particles
classification and naming of enzymes
enzymes usually have an -ase ending, with the first part of the word signifying the substrate or the type of reaction catalyzed
(ETS) protons flow back
into the inner chamber through pump molecules in the cristae, and their energy of movement is transferred to ATP
what is produced when we run out of oxygen
lactic acid
gated channels
may be opened or closed or inactive and may be triggered by any of a variety of stimuli
receptor-mediated endocytosis
membrane receptor molecules recognize substances to be brought into the cell
citric acid cycle is a repeating (cyclic) sequence
of reactions that occur inside the inner chamber of a mitochondrion; acetyl splits from COA and is broken down to yield waste CO2 and energy (in the form of energized electrons) which is transferred to ATP, NADH, and FADH2
chemical structure of enzymes
proteins of a complex shape
transport by pumps
pumps are membrane transporters that move a substance against their concentration gradient; opposite of diffusion
Citric acid cycle
pyretic acid (from glycolysis) is converted into acetyl CoA and enters the citric acid cycle after losing CO2 and transferring some energy to NADH
end product of glycolysis
pyruvic acid
general functions of enzymes
regulate cell functions by regulating metabolic pathways; specific in their actions
types of passive transport
simple and facilitated diffusion (channels and carriers); osmosis is a special example of a channel-mediated passive transport of water
permeable membrane
solutes permeate the membrane
Transcription can best be described as the:
synthesis of mRNA.
examples of allosteric effectors
temperature, hydrogen ion concentration, ionizing radiation, cofactors, end products of certain metabolic pathways
The two processes of protein synthesis are:
transcription and translation.
allosteric effectors
various chemical and physical agents that affect enzyme action by changing the shape of the enzyme molecules
aquaporins
water channels that permit rapid osmosis
osmotic pressure
water pressure that develops as a result of osmosis
If red blood cells containing 10% solute are placed in a solution containing 10% solute, what will happen?
Water will move into and out of the cells at equal rates.
facilitated diffusion
a special kind of diffusion in which movement of molecules is made more efficient by the action of transporters embedded in a cell membrane; transports substances down a concentration gradient; energy comes from the collision energy of the solute
What causes osmotic pressure to develop in a cell?
Osmotic pressure develops in the cell that originally had the higher concentration of impermanent solute. Osmotic pressure arises from the tendency of a pure solvent to move through a semipermeable membrane and into a solution containing a solute to which the membrane is impermeable.
A molecule or other agent that alters enzyme function by changing its shape is called a (an):
allosteric effector
anabolism
builds large molecules from smaller ones; usually consumes energy
examples of transport pumps
calcium pumps and sodium-potassium pumps
pumps
concentrate substances on one side of the membrane, as when storing an ion inside an organelle
pinocytosis
condition of cell drinking; fluid and the substances dissolved in it enter the cell
Facilitated diffusion is not an active transport process because it :
does not depend on cell energy.
Proteins that act as catalysts are called:
enzymes
osmosis results in
gain of volume on one side of the membrane and loss of volume on the other side of the membrane
three pathways of cellular respiration that are chemically linked
glycolysis, citric acid cycle, electron transport system
Red blood cells are placed in an unknown solution. After 45 minutes, the cells are examined and determined to have decreased in size. The unknown solution is:
hypertonic.
protein synthesis
is a central anabolic pathway in cells
oxidation-reduction enzymes
known as oxidase, hydrogenases, and dehydrogenates; energy release depends on these enzymes
simple diffusion
molecules cross through the phospholipid bilayer
vesicle-mediated (endocytosis and exocytosis)
move large volumes of substances at once, as in secretion of hormones and neurotransmitters
role of passive transport processes
move substances down their concentration gradient, thus maintaining equilibrium and homeostatic balance
enzymes that rearrange atoms within a molecule
mutases or isomerases
The component that distinguishes one nucleotide from another is the:
nitrogen base.
In the electron transport system, the final electron acceptor is:
oxygen
aerobic
oxygen
diffusion
passive process; molecules spread through the membranes; molecules move from and area of high concentrate, down a concentration gradient
glycolysis
pathway in which glucose is broken apart into two pyruvic acid molecules to yield a small amount of energy (which is transferred to ATP and NADH); includes many chemical steps (reactions that follow one another) each regulated by specific enzymes
two basic types of endocytosis
phagocytosis and pinocytosis
The cell process that involves microorganisms or other large particles being engulfed is called:
phagocytosis.
phosphorylating enzymes
phosphorylases or phosphatases; add or remove phosphate groups
passive transport processes do not require
any energy expenditure of the cell membrane
glycolysis is...
anaerobic (requires no oxygen)
hydrolyzing enzymes
hydrolase; digestive enzymes belong to this group
active site
where the enzyme molecule fits the substrate molecule; lock and key molecule
where does glycolysis occur
within the cytosol (outside the mitochondria)
Diffusion can be defined as:
the net movement of molecules from a region of higher concentration to a region of lower concentration.
Osmosis can be defined as:
the net movement of water molecules from a region of higher concentration to a region of lower concentration.
endocytosis
the plasma membrane "traps" some extracellular material and brings it into the cell in a vesicle
(ETS) as electrons are shuttled along a chain of electron-accepting molecules in the cristae...
their energy is used to pump accompanying protons (H+) into the space between mitochondrial membranes
hypertonic
"higher pressure"; cells placed in solutions that are hypertonic always shrivel as water flows out of them; this has great medical importance: if medical treatment causes the extracellular fluid to become hypertonic, serious damage may occur
RNA makes proteins by:
translation
citric acid cycles is also known as
Krebs cycle
potential osmotic pressure
the maximum pressure that could develop in a solution when it is separated from pure water by a selectively permeable membrane; knowledge allows prediction of the direction of osmosis and the resulting change in pressure
What is an allosteric effector? Give examples.
An allosteric effector is a molecule or other agent that alters enzyme function by changing its shape. Examples include certain antibiotic drugs, changes in pH, or changes in temperature.
Name as many passive processes that transport substances across a cell membrane as you can. How are they alike? How are they different?
Diffusion, dialysis, osmosis, facilitated diffusion, and filtration. Not all of these transport processes require cell energy to move substances across the membrane. They differ in how the substances move across the membrane. Dialysis is a form of diffusion in which the selectively permeable nature of the membrane causes the separation of smaller solute particles from larger solute particles. Osmosis is the diffusion of water across a semipermeable membrane. Filtration differs in that it moves substances across a membrane by the force of hydrostatic pressure. Facilitated diffusion uses carrier molecules that attract a solute, change its shape, and then release it to the other side of the membrane.
To what molecule must energy be transferred before it can be used by most cell processes?
Energy must be transferred to ATP before it can be used by most cell processes.
Describe the structure of an enzyme. How does its structure determine its function?
Enzymes are proteins and have the chemical properties of proteins. They are usually tertiary or quaternary proteins of complex shape. Enzymes often contain a nonprotein part called a cofactor. An important structural attribute of enzymes is the active site. The active site is the portion of the enzyme molecule that chemically "fits" the substrate molecule(s). This structure allows the enzymes to bind substrates together or unbind components of a substrate.
