BIOL 2160 Exam 2 - Scott Crousillac

Plasma Membrane

> semi-permeable

> small or Nonpolar molecules can freely diffuse across the membrane

> large or polar molecules need carrier proteins to move across membrane

Polar end

> Hydrophilic phosphate heads

Nonpolar end

> Hydrophobic fatty acid tails

Categories of Membrane Transport

> Passive Transport

> Active Transport

Passive Transport

> Transport across the membrane *does not require energy*

> Molecules move from high to low energy

> Ex: Solutes

> Molecules move down electrochemical gradient (high to low concentration)

Energy of a Solution

> Depends on solute concentration. The more solute, the more energy

Active Transport

> Transport across the membrane *requires energy*

> Molecules move up against their electrochemical gradient (low to high concentration)

How can ion concentrations vary in intracellular vs. extracellular solutions?

> Charged molecules can't cross without help of other proteins - no simple diffusion, so ion concentrations don't eventually even out

What determines the distribution of ions across the plasma membrane?

> Driving force

Driving Force

> Difference in energy across a membrane

> Force pushes from high to low energy

> Molecules are subject to 3 types

3 Types of Driving Force

1) Chemical

2) Electrical

3) Electrochemical

Electrical Driving Force

> Affects charge molecules (ions)

> Amount depends on *membrane potential*

> With a negative membrane potential: force on cations is inward & force on anions is outward

> Positive charge is attracted, Negative charge is repelled

> Amount of driving force depends on the specific value of the membrane potential and the *valence* of the permeant ion

Membrane Potential

> A difference in electrical potential or voltage across the plasma membrane

> At ANY time, will always be approaching the equilibrium potential of the MOST permeable ion

Electrochemical Driving Force

> Combination of chemical and electrical driving force

> Set by the *difference between the ion's equilibrium potential and the membrane potential*

Equilibrium Potential

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

Nernst Equation

> Mathematical expression of the Equilibrium Potential

K+ Concentrations

> Higher on the inside of the cell than the outside

> At rest, the inside of the cell is negative, relative to the outside

Chemical gradient of K+ at rest

> Tends to push K+ outside the cell

> Stronger then electrical gradient at rest.

[At equilibrium potential for K+ (-94mV), this is no longer the case]

Equilibrium Potential for K+

> -94mV

Electrical gradient of K+ at rest

> Tends to bring K+ into the cell

Chemical gradient of Na+ at rest

> Both chemical and electrical gradients tend to move Na+ into the cell

[At the equilibrium potential for Na+ (+55mV), this is no longer the case]

Na+ Concentrations

> Much higher on the outside of the cell than the inside

> At rest, the inside of the cell is negative, relative to the outside

Equilibrium Potential for Na+

> +55mV

Passive Transport Mechanisms

> Simple diffusion

> Facilitated diffusion

> Diffusion through ion channels

Simple Diffusion

> Movement of molecules as a result of *random thermal motion*

> Molecules freely cross membrane and net movement is down electrochemical gradient

> high to low w/o help, small non polar molecules

Facilitated Diffusion

> Molecules bind to specific protein "carriers" or *transporters* in the membrane that transport them down their electrochemical gradient

> protein ,changes shape

Diffusion through ion channels

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

Rate of simple diffusion is determined by:

> Driving force

> Membrane surface area

> Membrane permeability

Membrane Permeability

> Lipid solubility

> Size and shape of molecules

> Temperature

> Membrane thickness- if too thick no diffusion, only happens in short distances

Active Transport Mechanisms

> Primary

> Secondary

> low to high

Primary Active Transport or "pump"

> Uses ATP directly to provide energy to move molecules against their electrochemical ion gradient, usually negative

Secondary Active Transport

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

> 2 types

Types of Secondary Active Transport

> Contransport

> Countertransport

Cotransport

> These molecules move in the same direction

Countertransport

> These molecules move in opposite directions

Osmosis

> Movement of WATER across a membrane diluting it until there is equal concentration of solute on both sides of the membrane

> Always passive transport-high water concentration to low water concentration

Osmolarity

> Total solute particle concentration of a solution

Isotonic

> If intracellular solution and extracellular solution have the same solute concentration

Endocytosis

process by which a cell takes material into the cell by infolding of the cell membrane

Receptor-Mediated Endocytosis

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

> Many depression meds are SSRIs and block this in certain neurons

SSRIs (Selective Serotonin Reuptake Inhibitors)

> makes seroteen last longer

Exocytosis

a process by which the contents of a cell vacuole are released to the exterior through fusion of the vacuole membrane with the cell membrane.

Direct Signaling (Intercellular Communication)

> Cells that are physically connected to each other and touching.

> Connected by gap junctions

> Very fast and simple

> Cons: just small things, have to be connected so no long distance.

Indirect Signaling (Intercellular Communication)

> Involves a chemical messenger called a ligand binding to a receptor somewhere on a target cell

> Has to have a receptor for that messenger

Chemical Messengers

> Paracrines

> Neurotransmitters

> Hormones "Endocrine Signaling"

Ligands

> Paracrines, neurotransmitters, and hormones

> Bind to receptors and activate it

Paracrines

> "next to"

> Type of indirect signaling

> For short distance when cells not physically touching

Neurotransmitters

> Similar to paracrine but secretory cell is a neuron (nerve cell)

> Space between these 2 cells is a synapse

> Target cell can be another neuron, a muscle, or a gland

Hormones "Endocrine Signaling"

> All endocrine hormones enter blood stream and can affect many different target cells

> Pro: distance

> Con: Slower

Hydrophilic Messenger

> Polar, water-loving, can travel in the bloodstream as is

Hydrophobic Messenger

> Non-polar, water-fearing, doesn't want to be exposed to water so carrier molecule shields it from water in blood stream

Receptor Proteins

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

> Typically # of receptors on a cell is proportional to the # of receptors on a cell

Non-polar Signal Molecules

> Ex: steroid hormones

> Can penetrate the plasma membrane and interact with receptors inside the cell

Receptor Properties

> Specificity

> Affinity

Specificity

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

> How many ligands does the receptor bind to?

Affinity

> Strength of binding between a ligand and its receptor

> Measure of attraction, how strongly does it bond?

Receptor Activation Depends On

> Concentration of ligand: add more ligands

> Expression level of receptor: add more receptors

> Affinity of receptor for ligand: increase affinity between the 2 creating more binding between them

Relationship between ligand conc. [M] and receptor activation

> More [M] of messenger = more % of receptors bound

How can # of Receptors Change?

> Turnover (Degradation)

> Upregulation

>Downregulation

Upregulation

> Increase in receptor synthesis

Downregulation

> Decrease in receptor synthesis

Degradation (Receptor Turnover)

> Receptor synthesis --> Receptor Turnover =

direct intercellular communication

through gap junctions

indirect intercellular communication

chemical messengers

paracrine signaling

secreted molecules diffuse locally and trigger a response in neighboring cells

neurotransmission

the process of transferring information from one neuron to another at a synapse

hormones endocrine signaling

chemical messengers that are manufactured by the endocrine glands, travel through the bloodstream, and affect other tissues

membrane potential

always be approaching the equilibrium potential of the MOST permeable ion

> 2nd leading cause of death (20%) b/c of failure of cellular mechanisms that normallyly control cell divison

cancer

> a result of genetic that, often due to tumor promoting chemicals, hormones or viruses

cancer

proto-oncogenes

> normally promote cell division but are changed into oncogene by mutation that make the gene execcisively active

tumor-suppressor genes

> cause inactivation of growth genes allowing excessive cell division

caretaker genes

> regulate cell birth, cell death, and DNA damage repair genes

carcinogens

> environmental cancer-causing agents

HPV (human papilloma virus)

> causes arts on the skin, mouth, genitals, and larynx spread through physical contact with infected areas

> increases chances for cervical cancer> 3 rd most common cancer

> STD virus

> detected by pap smear

factors that increase an individuals risk of cervical cancer

> increasing age

> smoking

>lowered immunity

HPV vaccine

> Gardasil- targets cerivcal cancer and genital warts

> no virus, triggers immune response

receptor-dimerization

> same process hat occurs when PDGF normally activates its receptor at the plasma membrane causing sustained receptor activation and promotion of cell divison

plays a key role in angiogenses

> platelet derived growth factor

viruses that cause cancer

> hepatitis (B) and (C) viruses- liver infections that can develop into liver cancer (30%) spread through un-protected sexual contact or exchange fo blood

mutations

> somatic cells, often not passed on to offspring

> some can occur in germ-line cells and cans be passed

> tumors take years to accumulate

ovarian cancer

>8th most common cancer in women, 5th highest incidence of death

> surgery and chemotherapy

> cells must divide to repair

> can result in tumors if cell divison is excessive

ovulation

> process in which an ovarian follicle ruptures, and discharges an ovum tat bursts through the wall of he ovary

the pill

> oral contraceptive, relate cycle

> varying levels of progestin and estrogen hormones preventing follicular development and inhibit ovulation

> eliminates need for cell division

occupation serves no biological purpose if pregnancy is not desired t/f

true

oncogenesis

> cancer-forming process

>interplay b/w genetics and environment

tumor

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

> cells the proliferate quickly and are in abundant supply are the most dangerous

> cells are oxygen starved and require a blood supply to grow

metastasis

> leads to secondary tumors

> complex process and new tissues that arenon-random

tissues under attack are more vulnerable if they secrete growth factors and really grow new blood vessels t/f

true

tissues are more resistant if they produce

> anti-proliferative factors (block cell division)

> inhibitors of proteolytic enzymes (block cancer cell proteases)

> anti-angiogenesis factors (stop tumor cells from initiating the growth of blood vessels)

hypertonic

greater concentration

h20 always wants to move toward

hypertonic area

hypertonic

less than