bio exam 2

Consider a free ribosome. What enters this organelle, and what comes out of it, in the process of protein synthesis

Messenger RNA (mRNA) enters; a polypeptide comes out.

Consider a free ribosome. What enters this organelle, and what comes out of it, in the process of protein synthesis?

Messenger RNA (mRNA) enters; a polypeptide comes out.

At what stage of active transport is ATP needed?

for the transport protein to change its shape

Ions flow through __________ between cells of heart muscle. How does this help the heart do its job?

gap junctions; coordinate contraction

Why doesn't the antibiotic penicillin harm humans?

Human cells do not have cell walls. Penicillin inhibits an enzyme that bacteria use to make their cell walls; because humans do not have this enzyme, they are not harmed.

What is one way of reducing the effectiveness of a competitive enzyme inhibitor?

Increase the concentration of the substrate.

One model of the cell membrane is that it is a "fluid mosaic." What does this mean?

It consists of proteins suspended in a fluid phospholipid bilayer.

Water crosses the plasma membrane

through facilitated diffusion or diffusion. Water can cross the plasma membrane through the process of facilitated diffusion. However, water molecules can also cross the lipid bilayer directly.

Lysosomes contain digestive enzymes. Peroxisomes contain H2O2. Both the digestive enzymes and H2O2 can kill cells. How is it possible that cells can contain toxic substances without being damaged?

Membranes isolate substances into separate compartments.

A disease called primary ciliary dyskinesia is characterized by abnormal ciliary movements. In these cilia, microtubule functioning is disrupted due to microtubules missing an essential component. This disease could be caused by

Dynein is part of the proteins that make up microtubules. Defects in dynein proteins are responsible for this disease.

Which of the following is a correct statement about aquaporins?

Each aquaporin molecule allows billions of molecules of water to cross the plasma membrane each second.

Cells A and B are the same size and shape, but cell A is metabolically quiet and cell B is actively consuming oxygen. Oxygen will diffuse more quickly into cell _____ because _____.

B ... the diffusion gradient there is steeper As long as a metabolically active cell consumes oxygen as it enters, diffusion into the cell will continue because the concentration gradient favors movement in that direction

Which of the following is NOT an example of an organelle found in animals?

Cell walls are found in plants but not in animals.

_____ are found only in plant cells, but _____ are found in both plant and animal cells.

Central vacuoles; ribosomes Central vacuoles are found only in plant cells. Ribosomes are found in both plant and animal cells.

__________ energy is the type of __________ energy used to power the work of the cell.

Chemical; potential

What comes to mind when you hear the term "9 + 2"?

"9 + 2" refers to the structural arrangement of microtubules in both cilia and flagella. The arrangement consists of a central pair of microtubules ("2") surrounded by nine pairs of microtubules ("9").

The light microscope can magnify specimens by at most __________ times and can resolve details down to about the size of __________.

1,000; 0.2 µm

Most cellular work is accomplished by the consumption of __________, which energizes molecules by __________ them.

ATP ... phosphorylating The energy released when ATP is broken down is used to energize molecules by phosphorylating them.

What is meant by the term "enzyme specificity"?

An enzyme catalyzes only one type of reaction

Which plant cell organelle converts chemical fuel into packets of chemical energy that can power the cell?

Mitochondrion. In both plant and animal cells, it's the mitochondria that convert chemical fuel into packets of chemical energy that can power the cell.

In what way, if any, does osmosis differ from simple diffusion?

Polar water molecules cluster with hydrophilic molecules, so only free water diffuses down its concentration gradient

cell walls contain

Polysaccharides, cellulose, proteins

Which of the following is a function of the central vacuole?

Storing compounds produced by the cell One of the functions of the central vacuole is to store compounds produced by the cell.

When you hear "Substance X is moved against its concentration gradient," what do you think of?

Substance X has moved from a region of lower to a region of higher concentration with the help of AT

Which of the following is the most likely consequence for a cell lacking functional lysosomes?

The cell becomes crowded with undigested wastes A lysosome is a membrane-enclosed sac of hydrolytic enzymes that the cell uses to digest macromolecules and, in some cases, recycling the cell's own organic material.

Which of the following describes the function of the chloroplast?

The chloroplast converts light energy to chemical energy. The chloroplast makes food for the plant cell by converting light energy to chemical energy.

Which of the following components is external to the plasma membrane?

The extracellular matrix is external to the plasma membrane.

What is the relationship between the Golgi apparatus and the plasma membrane?

The finished products of the Golgi apparatus may leave the cell through vesicles that fuse with the plasma membrane. Transport vesicles from the Golgi move to the plasma membrane for export. In some cases the finished products become part of the plasma membrane or part of another organelle.

Your intestine is lined with individual cells. No fluids leak between these cells from the gut into your body. Why?

The intestinal cells are bound together by tight junctions. The membranes of neighboring cells are actually fused at a tight junction, forming a seal that prevents the leakage of extracellular fluid across a layer of epithelial cells.

According to the endosymbiont theory, what benefit was gained when the ancestor of the eukaryotic cell incorporated a photosynthetic prokaryote?

The newcomer provided nourishment to its host.

One function of the central vacuole in plant cells is facilitating cell growth: the central vacuole absorbs water and increases in size, expanding the volume and size of the plant cell while doing so. Animal cells, however, do not grow by this method. What is an essential difference between animal and plant cells that could explain how a plant cell can withstand the internal pressure caused by this expansion of the central vacuole?

The plant cell wall provides a rigid structure, preventing cell rupture.

Taq polymerase is an enzyme isolated from the organism Thermophilus aquaticus. This organism has been found living in the hot springs of Yellowstone National Park. This enzyme is used to copy human DNA from crime scenes. Most reactions are performed at ranges similar to those of the human body; however, what considerations should be made for optimum use of this enzyme?

The temperature should be raised These enzymes are not denatured by high heat and work more efficiently at temperatures of around 70-75°C. If the temperature is not increased, then the reaction will occur at a much slower rate.

Researchers used frog eggs to learn more about aquaporins. What characteristic of normal frog eggs was essential in these studies?

They are largely impermeable to water.

A pharmaceutical company wishes to focus on an enzyme to develop new medications. What type of initial study would be of the greatest benefit?

Understanding the enzyme's structure would help pharmaceutical companies design molecules that fit to the binding site and alter activity. Enzymes are the most common targets of drugs. By understanding the details of enzyme structure, new drugs can be designed and existing drugs can be better understood and potentially modified.

The sodium-potassium pump uses energy from ATP to move sodium ions out of the cell, and potassium ions into the cell. This is an example of

active transport. The sodium-potassium pump moves ions across the plasma membrane against their concentration gradients. This requires energy and is an example of active transport.

Utah's Great Salt Lake has an average salinity seven times higher than that of the oceans. Very few multicellular organisms live in this harsh environment. An example is the brine shrimp, which must devote a large portion of its metabolic energy to osmoregulation. These brine shrimp must

actively pump water back into their cells to counter its loss due to osmosis A cell (in this case, cells within the body of a brine shrimp) will experience a net output of water in a hypertonic environment. For cells to prevent shriveling, they must actively import water from their surroundings.

A plant cell placed into an isotonic solution __________. An animal cell placed into an isotonic solution __________.

becomes flaccid; neither swells nor shrivels

What effect do inherited lysosomal storage diseases have on cells

buildup of undigested material because key lysosomal enzymes are absent

Before refrigeration, meat was preserved by adding __________. What effect did this have on any contaminating bacteria or fungi?

concentrated salt solutions; plasmolysi

The movement of atoms, ions, or molecules from a region of higher concentration to regions of lower concentration is called _____.

diffusion Diffusion is the tendency of molecules to spread out in the available space. A substance will diffuse from an area of high concentration to an area of lower concentration.

Building a molecule of ATP is an __________ process. Hydrolyzing a molecule of ATP is an __________ process. This cycle is an example of __________.

endergonic; exergonic; energy coupling

The plasma membrane forms a pocket that pinches inward, forming a vesicle that contains material from outside the cell. This describes the process of

endocytosis In endocytosis, the plasma membrane forms a pocket that pinches inward, forming a vesicle that contains material from outside the cell.

A molecule moves down its concentration gradient using a transport protein in the plasma membrane. This is an example of

facilitated diffusion. In facilitated diffusion, molecules use a transport protein to move across the plasma membrane. There is a net movement of molecules down the concentration gradient -- that is, there is a net movement of molecules from where they are more concentrated to where they are less concentrated.

A researcher made an interesting observation about a protein made by the rough endoplasmic reticulum that was eventually used to build a cell's plasma membrane: the protein in the membrane was actually slightly different from the protein made in the ER. The protein was probably altered in the

golgi apparatus Vesicles carrying proteins from the ER fuse with the Golgi apparatus, where the proteins may be altered.

Mitochondria and chloroplasts are similar in that they both __________; however, they are different in that only chloroplasts, and not mitochondria, __________.

have a double membrane ... carry out photosynthesi Mitochondria and chloroplasts are both double-membraned organelle. However, mitochondria are the sites of cellular respiration and are therefore found in all eukaryotes, but only chloroplasts carry out photosynthesis.

cholesterol function in plasma membrane

helps to stabilize the structure of the plasma membrane

In the process of osmosis, water displays a net movement from an area of __________ water concentration to an area of __________ water concentration.

higher...lower Water displays a net movement down its concentration gradient. Movement down a concentration gradient is a characteristic of passive transport.

The plant cell wall

is a protective structure made of cellulose fibrils. The cell wall is a structure that protects the plant cell and is made of cellulose fibrils.

The maximum size of a cell is limited by _____.

its need for enough surface area to make exchanges with its environment Because volume increases at a faster rate than surface area, larger cells have proportionately less plasma membrane surface area.

microscope for internal structure

light transmission

Enzymes __________ the activation energy of a reaction. The energy change between products and reactants is __________ for a reaction that is catalyzed versus one that is not.

lower; the same

Which organelle plays a role in intracellular digestion?

lysosome The prefix "lyso-" means decomposition.

Which of the following are present in animal cells but not in plant cells?

lysosomes and centrosomes

Which of the following accurately matches the thinnest of a cell's cytoskeletal fibers, and their function?

microfilaments; muscle contraction

In active transport,

molecules move across the plasma membrane against their concentration gradient. Molecules move against their concentration gradient in active transport.

The synthesis of an amino acid follows this pathway: precursor A → intermediate B → amino acid C. Each reaction is catalyzed by a different enzyme. This metabolic pathway is controlled by feedback inhibition with amino acid C inhibiting the conversion of precursor A to intermediate B. Amino acid C acts as a _____ of the first enzyme in the pathway.

noncompetitive inhibitor In this form of feedback inhibition, the end product of the pathway inhibits an early-acting enzyme. Because the product of the pathway and the substrate of the early-acting enzyme are very different in structure, competitive inhibition is unlikely as this involves binding of an inhibitor to the active site. Much more plausible is noncompetitive inhibition in which the end product as inhibitor binds to a site on the enzyme that is different from the active site.

Ribosomal RNA is produced in the __________ according to instructions from the cell's __________. Subunits are then formed from ribosomal RNA and __________ imported from the cytoplasm

nucleolus; DNA; proteins

In eukaryotic cells the first step in protein synthesis is the _____.

transferring of information from DNA to messenger RNA Transcription is the first of the two main steps of protein synthesis.

The plasma membrane is selectively permeable. Which of the following can pass freely through the membrane with no assistance?

oxygen and carbon dioxide Oxygen and carbon dioxide, as well as other small, nonpolar molecules, can move freely across the membrane.

Both a living cell and an automobile convert fuel and __________ to the waste products __________. In the process, __________ is produced, which represents the entropy of the reaction.

oxygen; CO2 and water; heat

You have identified a new organism. It has ribosomes, plasmodesmata, and cell walls made of cellulose. This new organism is most likely a(n)

plant Plant cells have cell walls that are made of cellulose, and they have plasmodesmata, which are cytoplasmic channels that connect adjacent cells. Return to Assignment

Which of the following would distinguish a bacterial cell from an animal cell?

presence of a cell wall Prokaryotic cells have cell walls. Some eukaryotic cells do also, but animal cells do not.

Which of the following functions is performed by the Golgi apparatus?

processing proteins for secretion and for use within the cell

What is the function of the sodium-potassium pump in nerve cells?

pumping Na+ out of the cell and K+ into the cell

Which method of transport uses coated pits?

receptor-mediated endocytosis

Endergonic reactions __________ energy and result in products that have __________ potential energy than the reactants

require; higher

Which of the following structure(s) is/are found in prokaryotic cells?

ribosomes Both prokaryotic and eukaryotic cells do have ribosomes.

Which of the following are found in both prokaryotic and eukaryotic cells, but are organized in different ways.

ribosomes and DNA

The endomembrane system is in a constant state of renewal. Which organelle manufactures new membrane for this system?

rough endoplasmic reticulum

Select the substances that use facilitated diffusion to cross cell membranes.

sugars,ions,water,amino acids

Which of the following is a function of the rough endoplasmic reticulum?

synthesizing receptor proteins These proteins are made by the rough endoplasmic reticulum and then processed by the Golgi apparatus before being inserted into the cell membrane.

Osmosis is often viewed incorrectly as a process driven directly by differences in solute concentration across a selectively permeable membrane. What really drives osmosis?

the difference in water concentration across a selectively permeable membrane The driving force for osmosis is water's concentration gradient across a selectively permeable membrane. Differences in solute concentration across a membrane create water concentration differences, but solute concentration differences do not directly drive osmosis.

What controls the net direction of the movement of oxygen molecules in passive transport?

the direction of the oxygen concentration gradient

Recall from Chapter 4 that phospholipids have two parts: a nonpolar head and two nonpolar tails. In an oil-based, nonpolar environment, phospholipids would arrange themselves so that they __________.

would stay together but in a reverse orientation, with their tails projecting outward The fatty acid tails of a phospholipid remain nonpolar and the phosphate heads remain polar regardless of the surrounding environment. In a hypothetical, oily, and nonpolar environment, the tables are turned relative to water; the polar heads would cluster together to avoid exposure to the oil, and the nonpolar tails will project outward into the nonpolar, oil-based surroundings.