bio exam 2 CHAPTER 7

What are all of the organelles involved in the endomembranous network? What makes them similar?

- Nuclear Envelope, Plasma Membrane, Endoplasmic Reticulum, Golgi Apparatus, Lysosomes, and Vacuoles - similar because they all control synthesis of proteins and transports into membranes, organelles, or out of cells; Metabolism and movement of lipids; and Detoxification of poisons.

What three modern additions have been made to the cell theory?

1.) All cells have the same basic chemical composition 2.) All cells use energy 3.) All cells contain DNA that is duplicated and passed on as each cell divides.

What 4 traits are shared among all cells?

1.) Genetic material 2.) Ribosomes 3.) Cytoplasm 4.) Cell membrane

Which of the following results provided evidence of a discrete nuclear localization signal somewhere on the nucleoplasmin protein? a. The nucleoplasmin protein was small and easily slipped through the nuclear pore complex. b. After cleavage of the nucleoplasmin protein, only the tail segments appeared in the nucleus. c. Removing the tail from the nucleoplasmin protein allowed the core segment to enter the nucleus. d. The SRP bound only to the tail of the nucleoplasmin protein, not the core segment.

A

ER signal sequence

A short amino acid sequence that marks a polypeptide for transport to the endoplasmic reticulum, where synthesis of the polypeptide chain is completed and the signal sequence removed. The ER signal sequence typically is present in the first 20 amino acid residues and is removed when protein synthesis is complete.

Differentiate the structures of actin filaments, intermediate filaments, and microtubules.

Actin filaments are made up of two strands of actin monomers, intermediate filaments are made up of a number of different protein subunits, and microtubules are made up of tubulin protein dimers that form a tube. Actin filaments and microtubules exhibit polarity (or directionality), and new subunits are constantly being added or subtracted at either end (but added faster to the plus end).

Be able to describe the path of a molecule that is to be secreted at the cell surface. Start from the initial time of protein synthesis.

As they are being synthesized, secretory proteins enter the lumen of the endoplasmic reticulum. From the ER, vesicles transport these proteins to the Golgi, where they are sequentially modified and concentrated in a cis-to-trans direction. Secretory vesicles bud from the Golgi and move along cytoskeletal filaments to eventually fuse with the plasma membrane, secreting their protein cargo. Each of these transport steps requires specialized proteins to ensure that the cargo is sent to the proper location and is able to fuse with the target membrane.

What are three attributes of mitochondria and chloroplasts that suggest they were once free-living bacteria? a. The nucleoplasmin protein was small and easily slipped through the nuclear pore complex. b. After cleavage of the nucleoplasmin protein, only the tail segments appeared in the nucleus. c. Removing the tail from the nucleoplasmin protein allowed the core segment to enter the nucleus. d. The SRP bound only to the tail of the nucleoplasmin protein, not the core segment.

B

What has identical structure to a centriole?

Basal bodies and centrioles have identical structures.

Definition of endocytosis versus exocytosis.

Endocytosis: the process of capturing a substance or particle from outside the cell by engulfing it with the cell membrane, and bringing it into the cell. Exocytosis: the process of vesicles fusing with the plasma membrane and releasing their contents to the outside of the cell.

The eukaryotic cytoskeleton is a highly dynamic network of filaments and motor proteins. Which of the following correctly describe activities of these cytoskeletal components? Select True or False for each statement. T/F Myosin motors walk toward the plus ends of intermediate filaments. T/F Dynein motors are responsible for the whip-like movement of eukaryotic flagella. T/F Kinesin motors move vesicles along tracks toward the microtubule-organizing center. T/F Actin filaments are required for cytoplasmic streaming.

F, T, F, T. The first response is false because myosin walks along actin filaments. The third statement is false because kinesin moves vesicles to the plus ends, which are directed away from the microtubule-organizing center.

How many of these features does a typical bacterial cell have? DNA, cell wall, nucleus, ribosomes, cell membrane *

Four

What is the structure and function of the Golgi?

It has been likened to the cell's post office. A major function is the modifying, sorting and packaging of proteins for secretion. It is also involved in the transport of lipids around the cell, and the creation of lysosomes. The sacs or folds of the Golgi apparatus are called cisternae. - structure: membrane bound sacs

Compare the structure of prokaryotic cells to that of eukaryotic cells. What cell components do you find in bacteria?

It is a gel-like matrix composed of water, enzymes, nutrients, wastes, and gases and contains cell structures such as ribosomes, a chromosome, and plasmids. The cell envelope encases the cytoplasm and all its components. Unlike the eukaryotic (true) cells, bacteria do not have a membrane enclosed nucleus.

Which is true of a protein that has a nuclear localization signal?

It is made in the cytoplasm and transported to the nucleus

Which of the following is true of a protein that has a nuclear localization signal?*

It is made in the cytoplasm and transported to the nucleus

You look at a cell under a microscope during lab and your lab partner asks you if it is a prokaryotic cell. Which of the following clues could you use to answer them?*

It is part of a multicellular organism (because prokaryotes are unicellular)

What is one of the functions of microfilaments?

Microfilaments are a component of the cytoskeleton and provide the cell with structural support

What is the general function of the three cytoskeletal components?

Microfilaments are needed for cell contraction and changes in cell shape. Intermediate filaments form a strong scaffold for mechanical strength. Microtubules act as "trackways" for moving organelles and vesicles. Cytoskeleton: a network of protein tracks and tubules. It has several functions: - Structural support - Aids in cell division - Organelle transport - Cell movement

What is the structure and function of the mitochondria and chloroplasts?

Mitochondria: extract energy from food. PRODUCE ATP, mitochondria are organelles that function as "powerhouses of the cell" Chloroplasts: photosynthesis, makes glucose from sunlight with CO2 and H2O. Also gives plants its green color The inner membrane encloses the fluid stroma and contains stacked, hollow, membranous sacs (grana) made of individual thylakoids

What is the function of the nuclear localization sequences and the ER signal sequence? Where will you find a protein that is lacking both the nuclear localization sequence and the ER signal sequence?

Nuclear localization sequence : serves as a zipcode , contains 17 amino acids, allows them to enter the nucleus ER signal sequence : 20 amino acids, packages proteins, folds it, tells it how to fold and where to go a protein that is lacking both NLS and ER signal would be found in the cytoplasm

Compare and contrast the movement of (1) nucleotides and (2) large proteins through the nuclear pore complex. Which process would you expect to require an input of energy?

Nucleotides are small enough that they would diffuse through the nuclear pore complex along their gradients—a passive process that would not require energy. (2) Large proteins must be escorted through the nuclear pore complex in a directional manner—an active process that requires energy and results in the protein being concentrated inside the nucleus.

Which of these organelles produces H2O2 as a by-product?

Peroxisomes produce hydrogen peroxide as a by-product of their metabolic processes.

What is the function of the ribosome? Where is it made and where does it carry out its activity?

Ribosomes are a cell structure that makes protein. Protein is needed for many cell functions such as repairing damage or directing chemical processes. Ribosomes can be found floating within the cytoplasm or attached to the endoplasmic reticulum.

What are the functions of smooth and rough ER?

Rough ER: contains millions of membrane bound ribosomes, is involved with the production, folding, quality control and despatch of some proteins. Smooth ER: largely associated with lipid (fat) manufacture and metabolism and steroid production hormone production. It also has a detoxification function. calcium storage

Difference between diffusion of nucleotides vs larger molecules (DNA and proteins) into the nucleus:

Small molecules, like nucleotides, can freely diffuse into the nucleus. More selective with larger molecules

Most of the proteins that enter the nucleus possess a nuclear localization signal (NLS), even if they are small enough to pass through the nuclear pore complex unhindered. Why would a small protein have an NLS, when it naturally diffuses across the nuclear pore complex without one?

The NLS actively imports the protein into the nucleus, leaving very little of the protein in the cytoplasm. Diffusion alone would not drive all the protein into the nucleus.

How does the hydrolysis of ATP result in the movement of a motor protein along a cytoskeletal filament?

The binding and subsequent hydrolysis of ATP molecules cause conformational changes in motor proteins that result in their moving along the filament.

What is the role of the large central vacuole?

The main function of the large central vacuole in plant cells is to provide structural support; however, it serves other functions such as protection, storage, growth and waste disposal. This large central vacuole typically occupies at least 80 percent of the space in the cell.

What is the function of the nuclear envelope and the nucleolus? Know that chromatin and chromosomes are the same pieces of DNA, just in different conformations.

The nucleus stores chromatin (DNA plus proteins) in a gel-like substance called the nucleoplasm. The nucleolus is a condensed region of chromatin where ribosome synthesis occurs. The boundary of the nucleus is called the nuclear envelope, it is a membrane that encloses the nucleus. This bilayer membrane is made of lipids, and encases the genetic material in eukaryotic cells. The nuclear membrane is made up of a double lipid bilayer. The nuclear envelope has pores that allow the passage of materials into and out of the nucleus. Also called nuclear membrane.

When analyzing a sample of cells from a patient, you find the lysosomes are filled with undigested material. This observation makes you think that the lysosomes are not functioning properly. What are three different defects that could be responsible for malfunctioning lysosomes?

The patient may have a defect in (1) a hydrolytic enzyme that breaks down the undigested material, (2) the process of adding a mannose-6-phosphate signal to a lysosomal hydrolase, or (3) the mannose-6-phosphate receptor in the Golgi apparatus. Any of these three defects would result in lysosomes that are missing an enzyme necessary to break down the undigested material.

Pulse-Chase Experiment

The pulse-chase experiment is similar to fitting newly synthesized proteins with identification collars, much as one would do in the field to track animals. By using a chase, this cohort of newly synthesized proteins can be tracked as they move to different regions of the cell, without any subsequently synthesized proteins complicating the results. By tracking these proteins over time, the target region where the protein's function can be identified based on the concentration of radioactivity.

George Palade's research group used the pulse-chase assay to elucidate the secretory pathway in pancreatic cells. If they had instead performed this assay on muscle cells, where would you expect the labeled proteins to end up during the chase? (Muscle cells consist primarily of actin and myosin filaments and have high energy demands for muscle contraction.)

The radiolabeled proteins would likely be found in the cytosol and in mitochondria. Cytosolic proteins include proteins like the actin and myosin involved in muscle contraction. Because of the high energy demand, you would also expect many proteins needed for ATP production to be imported into mitochondria.

List the three cytoskeletal motor proteins and provide a distinct cellular role for each

The three motor proteins are myosin, kinesin, and dynein. Myosin is used to separate animal cells during cell division, for muscle contraction, and for cytoplasmic streaming. Kinesin is used for moving vesicles to the plus ends of microtubules. Dynein is used for moving vesicles to the minus ends of microtubules and for bending microtubules in flagella and cilia.

What are the three principles that are the foundation of the cell theory?

They have their own small, often circular chromosomes; they produce their own ribosomes; and they replicate independently of cellular division.

What is the general structure and function of the plasma membrane? How does a plasma membrane differ from a cell wall?

Whereas a cell wall consists of chitin, lignin, sugar, cellulose , and pectin among other molecules, the plasma membrane is mostly made up of the phospholipid bilayer. This difference makes a cell wall more elastic than the plasma membrane. Differences between the two can also be identified in their functions.

Describe the endosymbiont hypothesis?

a hypothesis about the origins of mitochondria and chloroplasts, which are organelles of eukaryotic cells. According to this, these originated as prokaryotic endosymbionts, which came to live inside eukaryotic cells.

Cells that line your intestines are known to possess a large number of membrane proteins that transport small molecules and ions across the plasma membrane. Which of the following cell structures would you expect to be required for this characteristic of the cells? the endoplasmic reticulum peroxisomes lysosomes the cell wall

a; the endoplasmic reticulum is responsible for synthesizing the membrane proteins required for the transport of solutes across the plasma membrane.

What is a lysosome?

an organelle in the cytoplasm of eukaryotic cells containing degradative enzymes enclosed in a membrane.

Which of the following cell structures would you expect to be most important in the growth of bacteria on the surface of your teeth? cell wall fimbriae flagella cilia

b; fimbriae are involved in bacterial attachment to surfaces and other cells, which would be important in the ability to grow on teeth.

In eukaryotic cells, the _______ synthesize(s) membrane components, proteins, and lipids*

endoplasmic reticulum

intermediate filaments

form a strong scaffold for mechanical strength. Give mechanical strength, move very SMALL things/vesicles from ER to Golgi; movement of smaller vesicles around the cell

golgi apparatus

modifies, stores, and packages products of the ER.

Microfilaments

needed for cell contraction and changes in cell shape. Give cell OVERALL SHAPE; cell (muscle) contraction

Microtubules

pull chromosomes apart during mitosis and cell division, move organelles, act as "trackways" for moving organelles and vesicles, move cell from one location to another

NLS

signal to send back to the nucleus

phagocytosis

some cells ingest smaller particles

function of smooth er

storing calcium, plays a role in detoxification and lipid synthesis.

What would happen if a cell stopped making properly functioning RNA?*

the cell would not be able to translate the information in DNA into protein

Nickname for nucleus function

the information center of eukaryotic cells—a corporate headquarters, design center, and library all rolled into one.

A mutant plant cell loses all of the chloroplasts in the cytoplasm. Which of the following outcomes will still occur?*

the plant will still be able to use carbohydrates as an energy source

Which statement most accurately describes what happens to proteins that lack an ER signal sequence?

they are released into the cytosol. Ribosomes synthesizing proteins without ER signal sequences remain in the cytosol and release the proteins there.