biol110 exam2

types of membrane transport (mvmt and need/ doesn’t need energy input)

• passive transport (diffusion)

  • movement of molecules across membrane from high → low conc.

  • doesn’t need energy input from cell

• active transport (anti-diffusion)

  • movement of molecules across membrane from low → high conc.

  • does require energy input from cell

passive transport w/o needing energy is

• simple diffusion

  • if PM permeable to particular molecule AND difference in conc. of molecule across membrane

  • molecule simple diffuses across membrane

    • no energy input / transport proteins needed

facilitated diffusion (FD)

• molecules that can’t cross membrane on own need this

• requires transport (transmembrane) proteins: channel & carrier proteins

  • selective; only transport certain molecules

• still driven by diffusion; doesn’t need energy input from cell

cells can regulate FD by…

1. regulating conc. of particular transport proteins in membrane

2. regulating activity of particular transport proteins

channel proteins in FD

• like tunnels (don’t touch/bind to molecules they transport)

  • channels can be 1. always open or 2. gated (opened or closed)

• direction of mvmt depends on conc.

  • mvmt doesn’t need energy input from cell

• selectiveness regulated by shape/design of protein

carrier proteins in FD

• must touch/bind to molecules they transport

• direction of mvmt depends on conc.

  • mvmt doesn’t need energy input from cell

• selectiveness regulated by binding sites of protein

3 basic types of carrier proteins (CP)

1. uniporters: CPs that only transport one type of molecule

2. symporters: CPs that transport two types of molecules, same direction at same time

3. antiporters: CPs that transport two types of molecules, opposite direction at same time

channel and carrier protein kinetics (rate of transport)

• channel proteins: linear kinetics

  • as solute conc. inc, rate constantly inc

• carrier proteins: saturation kinetics

  • slow inc, then rapidly inc, then levels off (S-shape)

active transport (anti-diffusion)

• used by cells to build up conc. gradient of a molecule across a plasma membrane

  • bc conc. gradients are critical for some biological processes

• needs 1. carrier proteins and 2. energy input from cell

membrane transport summary

transport across plasma membranes

• passive transport

  • simple diffusion (no transport proteins or energy input)

  • facilitated diffusion (no energy input)

    • channels

    • carriers

• active transport (needs energy input)

  • carriers

photo-bleaching experiments

unlabeled cell

→ membrane proteins labeled w flourescent dye

→ laser beam bleaches an area of cell surface

importance of maintaining fluidity level

• membrane too fluid: will not serve as a barrier; fall apart

• too solid: transmembrane proteins can’t flex (change shape) and carry out functions

  • ex. transmembrane transport and signaling proteins

how can cells regulate membrane fluidity, and what are the two ways for this

changing fatty acid chains of phospholipids

1. cell can generate phospholipids w/ more/fewer unsaturations in FA chains

2. cell can generate phospholipids w/ longer/shorter FA chains

FA saturation and membrane fluidity: MORE UNSATURATED FA

• pack less tightly

• if membrane is too solid, cell will inc. conc. of phospholipids w/ more unsaturated FA

FA saturation and membrane fluidity: MORE SATURATED FA

• pack more tightly

• if membrane is too fluid, cell will inc. conc. of phospholipids w/ more saturated FA

cells can _ the percentage of phospholipids that have more _ or more _ FA chains

change; saturated; unsaturated

FA length and membrane fluidity: shorter FAs

• pack less tightly (less SA/less interaction)

• if membrane is too solid, cells will inc. conc. of phospholipids w/ short FA chains

FA length and membrane fluidity: longer FAs

• pack more tightly (more SA/more interaction)

• if membrane is too fluid, cells will inc. conc. of phospholipids w/ long FA chains

cells can _ the percentage of _ with _ or _ FA chains, and when do these modifications happen

• change; phospholipids; long; short

• both at same time

if cells are exposed to lower temps, what happens to PM and how can the cell compensate?

• less fluid/ too soft

• make phospholipids w/ FA chains that are 1. shorter or 2. more unsaturated

if cells are exposed to higher temps, what happens to PM and how can the cell compensate?

• more fluid/ not soft enough

• make phospholipids w/ FA chains that are 1. longer or 2. more saturated

cholesterol and membrane fluidity

• cholesterol: ampipathic lipid; hydrophilic head group, hydrophobic ring structure, HC tail

  • present in plasma membranes of eukaryotic cells

  • helps regulate fluidity of plasma membranes

how can cholesterol help maintain solidity

steroid ring structure of cholesterol interacts with / partially immobilizes phospholipid FA chains

how can cholesterol help maintain fluidity

prevents phospholipid FA chains from packing together too tightly

what is hydrophobic interior

• what is PM permeable, less permeable, and not permeable to

major barrier for molecules crossing a PM

• PM is permeable to nonpolar molecules

• PM is less permeable to small polar molecules

• PM is not permeable to large polar molecules or ions

characteristics of life (6)

1. Organization and complexity (uses energy to actively maintain them)

2. Responds to environment: Actively maintain set of internal conditions within ideal ranges (homeostasis)

3. Growth and metabolism

4. Reproduction/heredity

5. Evolve

6. composed of 1+ cells

at most basic level, cells come in one of two types:

• prokaryotic: bacteria and archaea

• eukaryotic: animals, plants, fungi and protists

one major difference between prokaryotic and eukaryotic

eukaryotic cells can be 1000x larger than prokaryotic cells

cell volume represents

DEMAND – lots of metabolism occurring (greater volume=greater demand)

cell surface area represents

SUPPLY – everything that enters/exits the cell must go through its surface area

how do cells survive using terms of supply and demand

• To survive: SUPPLY > DEMAND

• As cell’s size increases, cell volume (demand) increases faster than the cell’s surface area (supply)

• So, at some point, demand begins to exceed supply

• Thus, remaining small allows cells to maintain a workable surface area to volume ratio.

prokaryotic cells

• Bacteria (also called eubacteria)

• Archaea (extremophiles)

  • small but dominant forms of life in both Biomass and Diversity

how are prokaryotic cells different than eukaryotic cells

• No nucleus, DNA is in an area of the cell, the nucleoid

• No internal membrane system

• All prokaryotes have cell wall: protective outer barrier made of peptidoglycans

eukaryotic and prokaryotic similarities

• DNA as their genetic material

• outer plasma membrane (Phospholipid bilayer)

• cytoplasm: semi solid substance w/ cell’s internal components

• ribosomes: synthesize proteins

eukaryotic cells: internal compartmentalization

• internal membrane system

  • Internal membrane-bound compartments called ‘organelles’ (little organs)

  • Different organelles in the cell perform different functions

nucleus functions

• Stores genetic information

• ribosome assembly

• RNA production (transcription)

nucleus structure

• Nuclear envelope: DLB membrane that defines the nucleus (inner & outer lipid bilayer)

  • Outer lipid bilayer is connected to SER & RER

• Nuclear pores: passages through nuclear envelope that regulate nuclear transport

• chromatin: Chromosomal DNA bound to DNA binding proteins

• nucleolus: area inside nucleus where ribosomes assembled (not organelle)

endomembrane system components

network of internal (lipid bilayer) membranes that includes:

• ER

  • SER: no ribosomes

  • RER: ribosomes on surface

• Golgi Apparatus

• Vesicles

ER structure

• Network of interconnected tubules

• Wall of tubules composed of a lipid bilayer

• lumen: space inside tubules

• SER & RER interconnected w/ each other and outer lipid bilayer of nuclear envelope

SER distinct functions

• lipid synthesis

• fatty acid desaturation

• cholesterol synthesis

• some carbohydrate synthesis

RER distinct functions

• Proteins are synthesized by RER-associated ribosomes, either:

  • bound for export from the cell

  • going to be associated with the outer plasma membrane

  • going to be used in the endomembrane system

  • *All other proteins synthesized by ribosomes in the cytoplasm

golgi structure

• Series of flattened tubes (sacs)

• Wall of tubes are lipid bilayer

• not connected to other structures

• cis face: receives transport vesicles from ER

• trans face: transport vesicles exit from Golgi

golgi functions

• Proteins & other molecules may be modified

• Molecules sorted by eventual destination

• Molecules released in vesicle

exocytosis

process by which material is exported out of the cell

• Example: production & export of insulin

endocytosis

material is “taken into” a cell via this

endocytosis specifics

specific process using receptors or non-specific taking up water and nutrients

1. PM traps materials from outside cell in endocytic vesicle

2. endocytic vesicle fuses w/ digestive vesicle (lysosome)

lysosomes definition and what happens

membrane bound vesicles with a low internal pH (4.5-5.0) that contains digestive enzymes

1. lysosomes “bud off” from trans face of golgi

• new lysosomes: primary lysosomes

2. primary lysosome fuses w/ endocytic vesicle or cellular organelle, forming secondary lysosome

lysosome function

to digest: material from inside/outside the cell

• (ex. worn out organelles is outside the cell)

tuberculosis bacterium process

• bacteria can prevent fusion of endocytic vesicle and primary lysosome, so TB avoids destruction and multiplies inside the cell

  • TB multiplies inside macrophage

  • kills macrophage

  • then infects and kills more cells

how many people does TB kill annually

2 million

mitochondria structure

DLB membrane

• outer membrane covers entire organelle

• inner membrane extensively infolded

  • folds are called cristae

  • liquid center is called matrix

mitochondria function

energy metabolism (ATP production)

endosymbiotic theory

• mitochondria/chloroplasts only arise from pre-existing mitochondria/chloroplasts (reproduce themselves)

chloroplast structure

double lipid bilayer membrane

• smooth outer and inner LB membranes cover entire organelle

• internal membrane organized into multiple stacks of disks within DLB

stack/disk names within chloroplast DLB

• thylakoid: single membrane disk

• granum: stack of thylakoids

• stroma: liquid substance surrounding the grana

chloroplast function

• site of photosynthesis in plant cells

• light energy converted into chemical energy

cytoskeleton structure

network of multiple types of proteins inside of cells

cytoskeleton functions

1. cell structure support

2. cell transport

3. helps mobile cells move

extracellular matrix structure

network of multiple types of proteins outside of cells

extracellular matrix functions

• structural support outside of cells

• glues cells into higher order structures (organs)

• cell-cell communication

plasma membrane

barrier; defines the inside/outside of a cell

PMs are _ barriers and why

selective

• regulates transport in/out of cells

PM is _ and cells can adjust _ and _

dynamic

• chemistry of PM

• molecules associated with the PM

what was known and not known in 1920s about membranes and phospholipids

• known: membranes were composed of phospholipids

• not known: how phospholipids were arranged in a membrane

evert gorter

• 1924: carried out a key experiment using RBCs

• wanted to determine if phospholipid membranes were “ 1 or 2 phospholipids thick”

why did dr. gorter use RBCs

1. easy to obtain

2. easy to count

3. of uniform size

explain dr. gorter’s experimental method

1. obtain and count RBCs

2. calculated total SA of RBCS (SA of 1 cell * total # of cells)

3. destroyed cells and collected membrane phospholipids (chemical separation)

4. placed phospholipids into chamber of liquid buffer → formed floating monolayer

5. measured total SA of phospholipids in chamber and compared it to total SA of the RBCs

what were the 2 possible outcomes of the RBC experiment, and what was the result?

1. SA of monolayer = SA of cells (1:1 ratio)

2. SA of monolayer is 2x SA of cells (2:1 ratio) (result)

what was the conclusion of the RBC experiment and what would the ratio have been if plasma membranes were double phospholipid bilayers

• cell membranes are phospholipid bilayers

• 4:1 (enough phospholipids to cover SA of each cell 4x)

how are plasma membranes much more than just a phospholipid bilayer (6)

• peripheral proteins

• transmembrane proteins

• polysaccharides

• cholesterol

• cytoplasm

• extracellular environment

fluid mosaic model of membranes

• how do phospholipid bilayer and its molecules relate? (analogy)

• plasma membranes are fluid structures

• phospholipid bilayer is like a lake and molecules float around in it

how do we know that membranes are fluid

cell fusion experiment (1970)

• mouse and human membrane proteins displayed increasingly intermixed membrane proteins over time in fused hybrid cells

• conclusion: proteins laterally diffusing around membrane, so membrane is fluid