BIOL 2160 - EXAM 2

What is the most widely accepted model of the cell membrane?

The fluid mosaic model

The Fluid Mosaic Model

A bi-layer of phospholipids with proteins inserted into and attached to it

Why FLUID?

The phospholipids move around and behave like a liquid

Why MOSAIC?

There are numerous different types of proteins and carbohydrates associated with it

Plasma membrane is _____ ?

Semi-permeable

What does it mean to be semi-permeable?

• Small or nonpolar molecules can freely diffuse across the membrane

• Large or polar molecules need carrier proteins to move across membrane

Why do phospholipids make ideal membranes?

There is water on the inside of the cell and the outside of the cell

_____ dissolves _____ ?

Like, like

Passive Transport

Transport across the membrane does not require energy

Active Transport

Transport across the membrane requires energy

In passive transport, molecules move across membranes from _____ to _____ energy?

High, low

Membrane Potential

The difference in charge between the inside and the outside of the cell

What are the main ions that determine the membrane potential for a cell?

Na+ and K+

There is more _____ outside the cell than inside, always?

Na+

There is more _____ K+ inside the cell than outside, always?

K+

How can ions cross the membrane?

With the help of membrane proteins

Driving Force

Difference in energy across a membrane, force pushes from higher to lower energy

What are the three types of driving force?

Chemical, Electrical, and Electrochemical

Electrical Driving Force

Affects charged molecules (ions)

What does electrical driving force depend on?

Membrane potential

Membrane Potential

A difference in electrical potential or voltage across the plasma membrane

What is the membrane potential at rest for most cells?

-70 mV

What is Electrochemical Driving Force determined by?

The combination of the chemical driving force and the electrical driving force

Equilibrium Potential

The membrane potential at which the electrical driving force on the ion is equal and opposite to the chemical driving force

How is the electrochemical driving force on an ion set?

By the difference between the ion’s equilibrium potential and the membrane potential

What is the equilibrium potential for Na+?

+55 mV

What is the equilibrium potential for K+?

-94 mV

The membrane potential, at ANY time, will always be approaching the equilibrium potential of the _____ permeable ion?

MOST

Simple Diffusion

Movement of molecules as a result of random thermal motion

Facilitated Diffusion

Molecules bind to specific protein “carrier” or transporters in the membrane that transport them down their electrochemical gradient

Diffusion through Ion Channels:

Molecules flow through pores in specific protein channels in the membrane down their electrochemical gradient

The rate of simple diffusion is determined by:

1. Driving force (concentration gradient)

2. Membrane surface area

3. Membrane permeability

Primary Active Transport

Uses ATP directly to provide energy to move molecules against their electrochemical gradient

Secondary Active Transport

One molecule moves passively down its electrochemical gradient to provide energy for another molecule to move up its electrochemical gradient

Cotransport

Move in the same direction

Countertransport

Move in opposite directions

What is the most important primary active transport mechanism in the body?

The Na+/K+ ATPase (also called a pump)

Osmosis

Movement of WATER across a membrane from an area of low concentration solute to an area of high concentration solute, diluting it, until there is equal concentration of solute on both sides of the membrane

Is osmosis passive or active transport?

Passive transport

Osmolarity

Total solute particle concentration of a solution

Isotonic

When intracellular solution and extracellular solution have the same solute concentration

Water will always move towards the _____ area?

Hypertonic

Endocytosis

The membrane surrounds a particle, enclosing it in a vesicle, and transporting it into the cell

Phagocytosis

Cell-eating. involves any non-specific solid particle

Pinocytosis

Cell-drinking, involves any non-specific fluid, or something dissolved in water

Receptor-Mediated Endocytosis

Binding of a SPECIFIC molecule to a receptor on a membrane, and transport of that molecule into the cell

Exocytosis

Endocytosis in reverse, large molecules are packaged in vesicles, which fuse with the membrane and release these molecules to the outside of the cell

Connexon

A protein channel that connects 2 cells in a gap junction, only good for short-distance signaling, but it is very fast

Indirect Signaling

A secretory cell releases a chemical messenger that binds to a receptor on a target cell

Paracrine Signaling

Involves 2 cells that are very close to each other, but are not touching

Endocrine Signaling

Involves a hormone being released into the bloodstream

Ligand

Anything that binds to a receptor

Receptor Proteins

A target cell receives a signal because it has receptor proteins specific to it on the plasma membrane or inside the cell

Specificity

Each type of receptor only binds one type of ligand/molecule

Affinity

Strength of binding between a ligand and its receptor

What does receptor activation depend on?

1. Concentration of ligand

2. Expression level of receptor

3. Affinity of receptor for ligand

Turnover

Destroying these receptors by sending them to the lysosome where they are broken apart

Upregulation

Increase in receptor synthesis

Downregulation

Decrease in receptor synthesis

All addictive drugs are _____ _____?

Artificial ligands

Opiates

Painkillers such as codeine, morphine, oxycodone, oxycontin, heroin, etc.

What do opiates bind to?

Endorphin receptors

Pharmacokinetic Tolerance

The result of lower concentrations of a drug actually reaching the receptor. Could be caused by degradation, or increased metabolism of the drug (nicotine)

Pharmacodynamic Tolerance

Cellular mechanism that results in receptor downregulation/turnover (opiates), or upregulation (nicotine)

Agonist

Ligands that bind to receptors and cause a biological response

Antagonist

Ligands that bind to receptors and do not cause a biological response

Signal Transduction

Refers to intracellular mechanisms that mediate response of target cell to chemical messenger

Lipophilic Messengers

Receptors typically intracellular

Lipophobic Messengers

Receptors on membrane surface

Second Messenger

An intracellular messenger produced by the binding of an extracellular messenger

Fast Channel-Linked Receptors

These channels open and allow ions to cross the membrane, this changes the membrane potential of the cell

Kinase

An enzyme that adds a phosphate group to another protein and activates that protein

Dimerization

Activates the kinase, which phosphorylates several proteins inside the cell

G-Proteins

Small intracellular proteins that link receptors with effector proteins

G Protein Coupled Receptors (GPCRs)

Receptors linked to G proteins

What are the three types of G-Proteins?

1. Ion channel regulation

2. Enzyme inhibiting (Gj)

3. Enzyme stimulating (Gs)

What are the 5 major second messenger pathways regulated by G-proteins?

1. cAMP (cyclic adenosine monophosphate)

2. cGMP (cyclic guanosine monophosphate)

3. IP3 (inositol triphosphate)

4. DAG (diacylglycerol)

5. Calcium

What is the 2nd leading cause of death in U.S.?

Cancer, kills > 600,000 people / year

What is cancer due to?

Failure of cellular mechanisms that normally control cell division

Genetic Damage

Often due to tumor-promoting chemicals, hormones, and sometimes viruses

What is the leading cause of death in the U.S.?

Heart disease

Genetic damage can result from a mutation in 1 of 3 types of genes:

Proto-oncogenes, tumor-suppressor genes, and caretaker genes

Proto-oncogenes

Normally promote cell division, but are changed into oncogenes by mutations that make the gene execessively active

Tumor-Suppressor Genes

Normally restrain growth. Mutations cause inactivation of these genes, allowing excessive cell division to occur

Caretaker Genes

Also linked to cancer. Normally protect genome

Apoptosis

Cell death

When caretaker genes mutate, they become _____?

Inactive

Carcinogens

Environmental substances that induce cancer-causing mutations in cells

Examples of Carcinogens include:

• UV radiation (excessive sunlight)

• Tobacco

• Asbestos

• Red meat

• Alcohol

• Benzene

• Lead

• Nickel

• Countless other chemicals…

HPV

Causes warts on the skin, mouth, genitals, and larynx. Spread through physical contact with infected areas

What % of women will get HPV in their lifetime?

80%

What is the HPV vaccine?

Gardasil

What are the three most common types of cancer in women?

#1 Breast, #2 Lung, #3 Cervical

Retroviruses

Viruses that do not have their own DNA, have RNA

HIV is a _____, while HPV is a _____ _____?

Retrovirus, DNA virus

Hepatitis (B) and (C) Viruses

Cause liver infections that can develop into liver cancer

Where do mutations mostly occur?

Somatic cells (non-germ-line cells)

Ovulation

Process in which an ovarian follicle ruptures, and discharges an ovum (egg), that bursts through the wall of the ovary

Oncogenesis

The cancer-forming process, result of an interplay between genetics and the environment

Tumor

A rapidly proliferating cell type that escapes normal growth restraints and stimulates the growth of vasculature to obtain oxygen