Chapter 3 Resources

Functions of Plasma Membranes

-Regulate the passage of substances into and out of cells and between cell organelles and cytosol. -Detect chemical messengers arriving at the cell surface. -Link adjacent cells together by membrane junctions. -Anchor cells to the extracellular matrix

a. Specify two ways in which acid secretion by compound X could be increased to 40 mmol/h.

1. Increasing the plasma concentration of compound X from 2pM, approximately 8 pM, as shown by the graph above 2.Increases the affinity of the binding sites for Compound X, This causes an increase in the amount of compound C that would bind to the membrane protein to stimulate acid secretion w/o increasing concentration of compound X. The more X binds to membrane proteins, the larger the amount of acid is secreted

What physiological function might tight junctions serve in the epithelium of the intestine, as shown in part (c) of this figure?

Because tight junctions form a barrier to the transport of most substances across an epithelium, the food you consume remains in the intestine until it is digested into usable components. Thereafter, the digested products can be absorbed across the epithelium in a controlled manner.

Identify the classes of organic molecules found in plasma membranes.

Cell membranes are composed primarily of lipids- phospholipids, steroid chloesterol and proteins.

List the three types of filaments associated with the cytoskeleton. Identify the structures in cells that are composed of microtubules.

Cytoskeleton filaments are the actin filaments, intermediate filaments and microtubules. Microtubules are found in the long processes of neurons and give the processes their shape. They also form the centrioles and spindle fibers that are important for cell divison

Peripheral membrane proteins

Location: At the plasma membrane surface where they are bound to the polar regions of the lipids in the interior of the membrane; in some cases to the charged polar regions of membrane phospholipids Characteristics: mediating metabolism of membrane components local transport of small molecules along the membrane or between the membrane and cytosol many are associated with cytoskeletal elements that influence cell shape and mobility

integral membrane proteins

Location: closely associated with the membrane lipids and cannot be extracted from the membrane without disrupting the lipid bilayer Characteristics: amphipathic=polar amino acid side chains (outward facing) in one region of the molecule and nonpolar (inward facing) side chains clustered together in a separate region transmembrane proteins-- most integral proteins that span the entire membrane

Describe the orientation of the phospholipid molecules in a membrane.

One end of a phospholipid has a charged or polar region, and the remainder of the molecule, which consists of two long fatty acid chains, is nonpolar; therefore phospholipids are amphipathic. (amphipathic--of or relating to a molecule that possesses both hydrophobic and hydrophilic properties)

Which plasma membrane components are responsible for membrane fluidity?

Phospholipids and Cholesterol

Describe the location and function of ribosomes.

Ribosomes are sites for protein synthesis. Bound to rough ER or free in cytoplasm. Proteins synthesized on free ribosomes are released into the cytosol of cell

Desmosomes

Structure: consist of a region between two adjacent cells where the apposed plasma membranes are separated by about 20 nm. The specialized area of the membrane in the region of a desmosome is usually disk-shaped; could be likened to rivets or spot welds. Function: Holds adjacent cells firmly together in areas that are subject to considerable stretching, such as skin The presence of numerous desmosomes between cells helps to provide the structural integrity of tissues in the body. Characterized by accumulations of proteins known as "dense plaques" along the cytoplasmic surface of the plasma membrane. The proteins serve as anchoring points for cadherins

Gap Junction

Structure: consists of protein channels linking the cytosols of adjacent cells Function: in the region of the gap junction, the two opposing plasma membranes come within 2-4 nm of each other, which allows for specific proteins (called connexins) from the two membranes to join, forming small, protein-lined channels linking two cells (1.5nm)

Tight Junction

Structure: forms when the extracellular surfaces of two adjacent plasma membranes join together so that no extracellular space remains between them; the tight junction occurs in a band around the entire circumference of the cell Function: blocks movement through extracellular space; causing organic nutrients to pass through the cell, rather than between them. NOT absolute= ions and water can pass through these junctions with varying degrees of ease with different epithelia.

What compartments constitute the entire intracellular fluid?

The intracellular fluid compartment includes all of the water in the cytoplasm plus the water in the nucleus.

b. Why will increasing the concentration of compound X to 28 pM fail to produce more acid secretion than increasing the concentration of X to 20 pM?

The plasma concentration of 20pM, compound X has most likely reached saturation of the membrane proteins. The membrane proteins are bound to compound X and promote acid secretion. So increasing the concentration of 20pm to 28pM, results in an increase in acid secretion. This is because the saturation limit for the membrane protein is reach and there is no empty binding sites for compound X to bind to

Smooth ER

are highly branced and tubular and do NOT have ribosomes. These organelles contain enzymes for fatty acid release and store intracellular Ca 2+

Rough ER

are network of flattened sacs that have ribosomes attached to their cytosolic surface. They package proteins synthesized on their attached ribosomes and send them to Golgi apparatus.

Describe the structure and primary function of mitochondria.

are spherical rod like structures that have both an inner and outer membrane. The outer membrane is smooth but the inner membrane is folded into sheets called cristae that extend into the matrix. Sites of most of energy production, in form of ATP

What functions do endosomes perform?

are vesicular structures, like the Golgi, are involved in sorting, modifying and directing traffic of vesicles in the cell

Lysosomes

contain acidic fluid and enzymes that can digest bacteria and cell debris that have been engulfed by the cell or damaged organelles

Identify the location of cytoplasm, cytosol, and intracellular fluid within a cell.

cytoplasm: region of the cell interior outside of the nucleus (contains cytosol and all other organelles) cytosol: intracellular fluid that surrounds cell organelles and nucleus (just the fluid, no organelles included) Largest intracellular fluid compartment. intracellular fluid: all the fluid inside the cell. (cytosol+nucleus+fluid inside all organelles)

What function does the nucleolus perform?

is the site of assembly of the RNA and protein components of ribosomal subunits

Which cell structure contains the enzymes required for oxidative phosphorylation? a. inner membrane of mitochondria b. smooth endoplasmic reticulum c. rough endoplasmic reticulum d. outer membrane of mitochondria e. matrix of mitochondria

matrix of mitochondria

What function does the Golgi apparatus perform?

modifies the proteins it recieves from rough ER and sorts modified proteins into specific classes of tansport vesicles that will be delivered to specific organelles of plasma membrane

Peroxisomes

use molecular oxygen to remove hydrogen atoms from various organic molecules including lipids, alcohol and potentially toxic ingested substances. They then destroy the toxic hydrogen peroxide formed