The cellular level of organization

Question 1

what is a generalized animal cell

Answer 1

It is at the cellular level or organization that activities essential to life occur and where disease processes originate.

A cell is the basic, living, structural, and functional unit of the body.

Question 2

All animal cells have four anatomical features in common. Name them.

Answer 2

1. Plasma (cell) membrane
2. Cytosol
3. Organelles
4. Inclusions

Question 3

Plasmalemma

Answer 3

The plasmalemma (cell or plasma membrane) is the
outer limiting membrane that separates the cell’s internal components from the extracellular material and external environment.

Question 4

Cytoplasm

Answer 4

Cytoplasm is the term used for all cellular material between

the plasma membrane and the nucleus of the cell.

Question 5

Cytosol

Answer 5

Cytosol is the thick, semi-fluid portion of the cytoplasm called
the intracellular fluid. It contains soluble proteins, enzymes, ions, and nutrients, and suspends the organelles.

Question 6

Organelles

Answer 6

Organelles are highly organized structures with characteristic shapes that are highly specialized for specific activities

Question 7

Inclusion

Answer 7

Inclusions are temporary structures suspended or stored

within the cytoplasm that contain secretions and storage products of the cell.

Question 8

What is the function of the cell membrane?

Answer 8

It is the thin barrier that separates the cell’s internal fluid from the external fluid. It serves as the gatekeeper that regulates passage of substances into and out of the cell

Question 9

Describe the fluid mosaic model of the membrane structure.

Answer 9

The fluid mosaic model of membrane structure describes the molecular arrangement of the cell membrane. The membrane is a mosaic of protein molecules “floating” like icebergs in a “sea” of lipid molecules

Question 10

Describe the three types of membrane lipids.

Answer 10

1. Phospholipids (75%) – hydrophilic “head” and hydrophobic
   “tails”
2. Glycolipids (5%) – role obscure (cell adhesion, recognition)
3. Cholesterol (20%) – membrane strength and steroid
   hormone precursor

Question 11

Compare integral membrane proteins with peripheral membrane proteins.

Answer 11

Integral proteins extend across the lipid bilayer into the extracellular fluid on one side and into the intracellular fluid on the other. They have a number of functions

Peripheral proteins do not extend across the lipid bilayer but rather are loosely attached to either the inner or outer surfaces of it. Their roles in cell function remain obscure.

Question 12

Channels (pore)

Answer 12

allows a specific substance to
move through water-filled passageways. Most cell membranes include specific channels for several ions. Most common are for Na+ and K+

Question 13

Transporter (carrier

Answer 13

– transports specific substances
across membrane by changing shape. For example, amino acids, needed to synthesize new proteins, enter body cells via transporter.

Question 14

Receptor

Answer 14

recognizes a specific ligand and alters the cell’s

functions in some way. For example, this is a classic mechanism by which protein-based hormones affect cells.

Question 15

Enzyme

Answer 15

catalyzes reactions inside or outside (depending

upon which direction the active site faces) the mem-brane. *ex. small intestinal enzymes for digestion of food)

Question 16

Cytoskeleton anchor

Answer 16

anchors filaments and tubules of the
cytoskeleton inside cell membrane to provide struc-tural stability and shape for the cell. May also partici-pate in movement of the cell.

Question 17

Cell identity markers

Answer 17

distinguish your cells from anyone 
else’s (unless you are an identical twin) and from microbial cells.  An important class of such markers is the histocompatibility (MHC) proteins.

Question 18

List the three major functions of the cell membrane.

Answer 18

1. Communication
2. Electrochemical gradient
3. Selective permeability

Question 19

With what must cells of the body be able to communicate?

Answer 19

The cell, via the plasma membrane, communicates with other body cells, foreign cells, and ligands (neurotrans-mitters, enzymes, hormones, nutrients, and antibodies) in the extracellular fluid.

Question 20

Describe the chemical and electrical components of the electrochemical gradient formed by the cell membrane.

Answer 20

The chemical portion of the gradient is formed because the membrane maintains very different chemical compositions in the cytosol and the extracellular fluid.
*The major extracellular cation is Na+ and the major
anion is Cl-
*The major intracellular cation is K+ and the major
anions are organic phosphates and amino acids.

The electrical gradient arises because the inside of the membrane is more negatively charged than the outside. As a result, there is a voltage (voltage is electrical potential or potential difference as expressed in volts.) called the membrane potential across the membrane.

Question 21

The third major function of the cell membrane is to provide selective permeability. What is this?

Answer 21

The plasma membrane regulates the entry and exit of materials by permitting certain substances to pass freely while restricting the passage of others. This property is called selective permeability.

Question 22

A membrane is said to be permeable to a substance if…

Answer 22

It allows that substance free passage into and out of the cell.

Question 23

Solubility in lipids

Answer 23

Substances that dissolve in lipid pass
easily across the membrane while water-soluble substances do not. For example: oxygen is fat-soluble and crosses the membrane easily; glucose is water -soluble and does not cross the membrane.

Question 24

how does size effect soluability

Answer 24

Ions and molecules less than 8 Angstroms in
diameter can cross the cell membrane freely. Substances larger than 8 Angstroms are restricted from crossing the membrane because they are too large to pass between the molecules that form the membrane itself.

Question 25

how does charge effect soluability

Answer 25

The membrane is impermeable to all charged ions
and molecules. However, the overall negative membrane potential of most cells aids the influx of cations and hinders the influx of anions.

Question 26

how does Presence of specific channels or transporters effect solubility

Answer 26

Channels increase membrane permeability for some substances by providing specific routes of entry or exit. This is done by either attaching to and shuttling the substances through the channel or by simply letting it pass through the channel’s water-filled space.

Question 27

Why are the mechanisms that enable substances to move across cell membranes essential to life?

Answer 27

Without these mechanisms the cell would be unable to procure oxygen, nutrients, etc., or rid itself of carbon dioxide and other waste products of metabolism.

Question 28

Compare passive processes with active processes.

Answer 28

Mechanisms that move materials across the cell membrane without the
use of cellular energy are called passive processes.

Mechanisms that move material across the plasma membrane with the
use of cellular energy are called active processes.

Question 29

List the four passive processes.

Answer 29

1. Simple diffusion
2. Osmosis
3. Filtration
4. Facilitated diffusion

Question 30

List the four active processes

Answer 30

1. Primary active transport
2. Secondary active transport
3. Endocytosis
4. Exocytosis

Question 31

Describe the process of diffusion. What is the concentration gradient? How do substances move from one area to another

Answer 31

Passive processes depend upon pressure or concentration differences (gradients).

Simple diffusion – Since all substances have kinetic energy,

they are constantly moving about, colliding into one another and then moving off into various directions.

This random mixing of ions and molecules in a solution due to their kinetic energy is called diffusion. (Latin “diffusus”= to spread out)

If the substance is present in high concentration in one area, the difference in concentration between the two areas is said to be the concentration gradient.

When two such areas are connected (Ex. by water or air) more particles diffuse from the area of high concentration than from the area of low concentration. There is, therefore, net diffusion, from the area of high concentration to the area of low concentration.

Substances undergoing net diffusion (from high to low concentration) are said to move down or with their concentration gradient.

After a period of time, the particles become evenly distributed throughout the connected areas and a uniform concentration or equilibrium is reached so that no more net diffusion occurs.

Question 32

Describe the process of osmosis. What is an osmotic gradient? Distinguish between isotonic, hypotonic, and hypertonic solutions

Answer 32

Osmosis is the net movement of water through a selectively permeable membrane.

In osmosis, water moves across the membrane from an area of higher water concentration to an area of lower water concentration until a uniform water concentration is reached.

For this to occur, there must be a solute in the water to which the membrane is impermeable; therefore, no solute can cross the membrane to satisfy the diffusion gradient.

This movement of water through the selectively permeable membrane generates a pressure called the osmotic pressure.

To maintain normal shape, a cell must be bathed in an isotonic solution. This is a solution in which the total concentrations of water molecules and impermeable solutes are the same on both sides of the membrane.

Under these conditions, while the membrane remains impermeable to almost all solutes, water molecules enter and leave the cell at the same rate, so that there is no net osmosis, allowing the cell to maintain its normal shape and volume.

A hypotonic solution is one that has fewer solutes than cells have. A cell placed in such a solution will have a net osmosis into the cell, causing it to swell and burst.

A hypertonic solution has a greater concentration of solutes that do cells. A cell placed in such a solution will have a net osmosis out of the cell, causing the cell to shrink (crenate).

Question 33

Describe the process of filtration.

Answer 33

In this passive process, water and solutes move across a cell membrane due to gravity or hydrostatic (water) pressure.

Such movement is always from an area of high filtration pressure to an area of low filtration pressure.

Example: movement across the capillary walls due largely to blood hydrostatic pressure.

Question 34

What is facilitated diffusion? What three factors determine its rate?

Answer 34

Some substances are too large to pass through membrane channels and too lipid-insoluble to diffuse through the lipid bilayer.

Such substances may move through the membrane with the aid of transporter proteins, moving down their concentration gradient to a region of lower concentration.

This process is called facilitated diffusion. It can be much faster than a simple diffusion and depends on three factors:

(1) concentration gradient
(2) number of transporters available
(3) rate at which transporter and substrate combine

Question 35

What are active processes? Describe a primary active transport process by discussing the Na-K ATPase membrane pump.

Answer 35

When cells actively participate in moving substances across membranes, they must expend energy by splitting the ATP molecule.

Using the released energy from ATP, the cell then moves substances against their concentration gradients, from an area of low concentration to and area of higher concentration.

Primary active transport – Energy from ATP is used to directly move substances across the membrane by changing the shape of transport (pump) proteins in the membrane.

Na+ in the cytosol binds to the pump protein. Remember that Na+ is the major extracellular cation whereas K+ is the major intracellu-lar anion

Na+ binding triggers the breakdown of ATP and the attachment of the released high-energy phosphate group to the pump protein. This changes the shape of the protein so that the Na+ ions are pushed through the membrane and expelled from the cell.

K+ binding to the transport protein triggers release of the phosphate molecule. This again causes the shape of the transport protein to change. As the pump returns to its original shape the K+ is pushed through the membrane and into the cytosol. At this point the pump is ready to bind Na+ again and renew the process.

Question 36

Describe secondary active transport. How is it different from primary active transport?

Answer 36

The energy stored in ion gradients drives substances across the membrane. For example, using primary active transport, a nerve cell forms 14x more Na+ outside the cell than inside. If channels for Na+ open, the Na+ ions move into the cell by diffusion.

Energy was required to create the diffusion gradient, therefore this is considered to be a type of active transport.

Question 37

What is exocytosis?

Answer 37

Exocytosis is an active transport process whereby the cell expends energy to actively discharge large substances from the cell. Example: secretion from glands

Question 38

What is endocytosis? Name and define the three types of this process.

Answer 38

Endocytosis is the process by which large substances are actively taken into the cell.

1. Phagocytosis – “cell eating”
2. Pinocytosis – “cell drinking”
3. Receptor-mediated endocytosis – specific ligands are taken
   into the cell by attaching to membrane receptors and being carried into the cell.

Question 39

Nucleus

Answer 39

The nucleus is a spherical or oval membrane-bound organelle

that contains the heredity material (DNA) of the cell and is there-fore considered to be its control center.

Question 40

Nucleolus

Answer 40

The nucleolus is a nonmembrane-bound spherical body
within the nucleus composed of DNA, RNA, and proteins. It functions in the synthesis and storage of ribosomal RNA and is therefore necessary for protein synthesis within the cell

Question 41

Ribosome

Answer 41

Ribosomes are organelles in the cell cytoplasm, composed

of ribosomal RNA and ribosomal proteins. They function in the synthesis of proteins

Question 42

Smooth Endoplasmic Reticulum

Answer 42

Endoplasmic reticulum is a network of
membrane-bound channels running through the cytoplasm. It serves in intracellular transport, support, storage, synthesis, and packaging of molecules.

Question 43

Golgi complex

Answer 43

The Golgi complex is a cytoplasmic organelle consisting
of 4-6 flattened membranous sacs stacked upon one another. It functions in processing and packaging materials destined for secretion from the cell, for use by the cell membrane, or for use by the lysosomes.

Question 44

Lysosomes

Answer 44

Lysosomes are membrane-bound organelles that contain
very strong digestive enzymes. They function in destruction of intracellular debris and are used extensively for destruction of foreign matter ingested by phagocytes

Question 45

Peroxisomes

Answer 45

Peroxisomes are membrane-bound organelles that
produce hydrogen peroxide, which is then used to oxidize a number of toxic substances. This function is particularly important n the liver and kidneys.

Question 46

Microfilaments

Answer 46

Microfilaments are rodlike, protein structures (about 6nm
in diameter). They provide the contractile apparatus in muscle cells and are used by other cells for support, shape, and movement

Question 47

Microtubules

Answer 47

Microtubules are cylindrical protein filaments (18-30 nm

diameter) that provide support, structure, and transportation routes within the cell.

Question 48

Flagellum

Answer 48

A flagellum is a long hairlike, motile process that extends

from the cell and is used for locomotion

Question 49

Cilia

Answer 49

Cilia are short, hairlike processes that extend from some cells.
They are used primarily to sweep materials across the cell surface.

Question 50

Centrioles

Answer 50

Centrioles are paired cylindrical structures associated with
ciliary function and cell division.

Question 51

Briefly describe the process of transcription and its processes?

Answer 51

Transcription, occurring in the nucleus, is the process by which the genetic information found within DNA is encoded and is copied onto a strand of RNA.

Question 52

what are the Three forms of RNA are created

Answer 52

1. Messenger RNA (mRNA) directs synthesis of proteins
2. Ribosomal RNA (rRNA) joins with ribosomal proteins to form
   the ribosomes where proteins are made
3. Transfer RNA (tRNA) binds to amino acids

Question 53

Briefly describe the process of translation and its product.

Answer 53

Translation, occurring at ribosomes in the cytoplasm, is the process by which the nucleotide sequence of mRNA specifies the amino acid sequence of a particular protein.

Question 54

SOMATIC CELL DIVISION

Answer 54

In this type of cell division, a single starting cell called the parent cell divides to produce two identical daughter cells.

This type of cell division consists of a single nuclear division called mitosis and a single cytoplasmic division called cytokinesis.

Question 55

why is somatic cell division important and what does it do for us

Answer 55

This mechanism ensures that each daughter cell has the same number and kind of chromosomes as the original parent cell.

We use mitosis to replace dead or injured cells with like cells and to