bio exam 2

units 5, 6, 7, 8

What are all living cells surrounded by

a membrane

What do membranes do

provides a selective boundary between internal cell and external environment

what is a cell membrane composed of

lipids, proteins, and carbs arranged in a dynamic structure

Membrane Transport

controlling what enters and leaves

Cell signaling

receiving and processing information

Fluid Mosaic Model

a flexible phospholipid bilayer with proteins embedded and able to move within it

What happens when proteins and lipids cluster into regions

specialize in functions such as transport, signaling, or recognition.

What do carbs (glycolipids/glycoproteins) do when attacted to membrane surfaces

help cells identify and communicate with one another

Phospholipids

form the bilayer structure that creates a stable barrier between the cell and its environment

Cholesterol

regulates membrane fluidity, preventing it from becoming too rigid in cold conditions or too fluid in warm conditions

Glycolipids

carbohydrate groups that project from the cell surface, playing key roles in cell to cell recognition and communication

Lipid Raft

microdomains enriched in cholesterol and glycolipids that organize proteins for signaling and transport

Membrane fluidity

hydrophobic interactions, certain proteins are anchored in by cytoskeleton or extracellular matrix

Lipids in fluid membranes

move rapidly within the bilayer, shifting sideways with ease

Proteins in fluid membranes

move more slowly; some drift randomly while others move in a directed way

Low temp effects on fluid membranes

phospholipid movement slows and membrane is less fluid, sometimes membranes undergo a transition to a more rigid state, this temp depends on lipid composition

Saturated fatty acids effect on membrane fluidity

straight and pack closely, which reduces membrane fluidity

Unsaturated fatty acids on membrane fluidity

contain kinks that prevent tight packing, which helps the membrane remain fluid at lower temperatures

Cholesterol in membrane fluidity

buffer that stabilizes membrane fluidity, prevent from becoming excessively rigid at low temperatures or excessively fluid at high temperatures

Cholesterol membrane fluidity in high temps

restrains the movement of phospholipids and prevents excessive fluidity

Cholesterol membrane fluidity in low temps

disrupts tight packing of phospholipids and helps maintain flexibility

Integral proteins

lipid bilayer, spanning it completely (transmembrane proteins), nonpolar regions interact with the hydrophobic core, often forming α-helices.

Peripheral proteins

Loosely attached to the surface of the membrane, do not penetrate the lipid bilayer, connect to other proteins or to the cytoskeleton

Membrane compartments in cell-to-cell region

Membrane carbohydrates are covalently attached to lipids (forming glycolipids) or, more commonly, to proteins (forming glycoproteins)

why do carbohydrate patterns vary among species

individuals, and even cell types, giving cells a “molecular identity tag

what do carb tags help with

binding sites for antibodies, toxins, viruses, enzymes, and other cells, influencing immune defense, infection, and communication

cytoplasmic

inner of membrane

extracellular

outer membrane

how is membrane sidedness set up

when the membrane is being built in the ER and Golgi, which places proteins, lipids, and carbs in specific orientations

sidedness recognition

carbohydrates n glycoproteins and glycolipids are displayed on the outer surface so cells can id each other

Signaling Sidedness

receptors must face outward to detect signals from the environment

Transport Sidedness

channels and pumps are positioned so molecules move in the right direction

Selective permeability

allowing some substances to cross more easily then others

what is regulating transport across cellular boundaries essential for

cell survival

what does selective permeability depend on

hydrophobic interior of the lipid bilayer, size, charge, and polarity, presence of specific channels and carrier proteins

how can substances cross the cell membrane

passive transport, active transport, endocytosis and exocytosis

How do hydrophobic, nonpolar mol. interact with the lipid bilayer

dissolve in lipid bilayer, cross easily

How do small uncharged polar mol interact with the lipid bilayer

pass through more slowly than small nonpolar mols.

How does water interact with the lipid bilayer

slowly, aquaporins allow much faster water movement

How do ions and large polar mols interact with the lipid bilayer

require transport proteins

What is membrane permeability influenced by

molecular polarity

Transport Proteins

allow for passage of hydrophilic substances across the membrane, selective

Channel proteins

transport proteins that have a hydrophilic channel that certain mols. or ions can use as a tunnel, selective

Carrier proteins

bind to mol. and change shape to shuttle them across the membrane, selective

Aquaporioins

for facilitated diffusion of water

ion chanel’s

transport ions

gates channels

open or close in response to stimulus

facilitated diffusion

carrier proteins undergo subtle changes in shape, can be triggered by binding and release of transport molecules, no net energy required

Active transport

moves substance against gradient, requires energy, sodium potassium pump

membrane potential

voltage across a membrane, created by unequal distribution of positive and negative ions

voltage

provides energy influencing how charged substances move

what drives ion movement

electrochemical gradient, chemical force, electrical force

chemical force

differences in ion concentration

electrical force

the effect of charge across membrane

what do electrogenic pumps generate

voltage, sodium potassium pump in humans, proton pump in everything else, create ion gradients, transport n cell signals

Cotransport

one substance moving with gradient provides energy to move another substance against its gradient

Cotransport in transport proteins

link the flow of one mol. to the movement of another

Cotransport in plant cells

proton pumps create a hydrogen ion gradient

Cotransport stored energy gradient

can be used to actively bring in nutrients such as sucrose

bulk transport

active, exocytosis, endocytosis

Exocytosis

cells release large mols. outside of the cell, often used in secretory cells

where do secretory vesicles often originate from

golgi apparatus or from recycling of existing vesicles membranes

what does vesicle membrane fuse to

plasma membrane

endocytosis

cell takes in molecules and particulate matter by forming new vesicles from the plasma membrane

phagocytosis

solid material/substance entering the cell

pinocytosis

sampling local environment, dissolved in extracellular fluid

receptor mediated endocytosis

taking specific smaller things attached to outer receptors and bringing them in

cell signaling

cells must constantly communicate to survive and function, different types depending on length needed for travel

what are signals carried by

ions, proteins, or small chemicals

what do signals allow cells to do

detect changes, coordinate with other cells, control growth, development, and immune defenses

Local Signaling

direct cytoplasmic communication, autocrine signaling, paracrine signals, synaptic signals

Direct cytoplasmic communication

gap junction in animals, plasmodesmata in plants

Autocrine signaling

a cell responds to a signal it releases

Paracrine signaling

a secreted signal which acts on nearby cells

synaptic signaling

a neuron releases a neurotransmitter across a synapse

Long distance signal

endocrine

How do animal hormones travel

bloodstream

How do plant hormones travel

vascular tissue, diffusion, pass from cell to cell

what process do cells reviving signals undergo

reception, transduction, response

reception

detection of the signal, when ligand bonds to a specific receptor

transduction

conversion of the signal to a cellular response via a signal transduction pathway

response

a cellular activity in response to the signal

Cell Surface receptors

in plasma membrane, usually bind hydrophilic ligands

types of cell surface receptors

g protein coupled receptors, ion channel linked receptors

internal receptors

inside cell bind hydrophobic ligands, often regulate gene expression

G Protein Coupled Reactors

membrane proteins that work with G proteins inside of the cell, molecular switches

What happens to G protein before signal

inactive and bound to GDP

What happens when ligand binds to GPCRs

receptor changes shape and causes GDP to be replaced by GTP

What happens to GTP-bound G protein

activates other proteins inside the cell, leads to a cellular response

What turns of GPCRs

the g protein breaking down GTP to GDP

Ligand Gated Ion Channel

“gate” for ions, channel opens and allows for ions to flow through, triggering a cellular response

why are ligand-gated ion channels important to the nervous system

ion movment can create electrical signals

Intracellular Receptors

small hydrophobic messengers, cross plasma membrane to bind to receptors

Where are intracellular receptors found

cytoplasm or nucleus of target cells

Transduction

amplifies signal, multiples times inside the cell, one can activate many

Two common mechanisms for signal transduction

second messengers, protein phosphorylation

what are Second Messengers

small mol. or ions that carry a signal inside the cell

Ligand, Second messenger

First messenger, activates receptor, triggers production/release of second messenger

Second Messengers

spread quickly inside the cell because they are small and diffuse easily

Protein Phosphorylation

signaling pathways, cascades can amplify the signal because one kinase can activate many protein mol