ch 5 membrane structure & function structure traffic across –passive transport diffusion...
TRANSCRIPT
Ch 5 Membrane Structure & Function• Structure
• Traffic across– Passive
transport• Diffusion• Osmosis• Facilitated
diffusion– Active transport– Endo &
exocytosis
Functions of Membrane Proteins• Transport• Enzyme activity• Signal
transduction• Intercellular
joining• Cell to cell
recognition• Attachment to
cytoskeleton
Structure of Membrane• Phospholipids &
proteins• Fluid mosaic
model• Factors that affect
fluidity:– Fatty acid type– Temp
• Types of proteins– Integral– Peripheral
Traffic Across Mem• Selective permeability
(ease & rate) depend on 2 things:1. discriminating barrier of lipid bilayer– Impermeable to larger
polar & ions– Perm to nonpolar – How about water?
2. Transport proteins
Remember diffusion…
Traffic Across Membrane
Osmosis• Why important?• Relative terms
used to compare concentration of inside vs outside of cells– Hypertonic – Hypotonic– Isotonic
• Water always moves toward hypertonic
• Solutes move from high to low concentration.
Animal cells in hypotonic & hypertonic solutions
Cells in a hypotonic solution gain water & swell; possibly burst if no cell wall.
Cells in a hypertonic solution lose water & shrink.
Cells in an isotonic solution have no net gain or loss of water.
Osmoregulation – control of water balance• Ex of how orgs
stabilize water loss & uptake:– Freshwater
paramecium
OsmosisEx of how orgs stabilize water loss & uptake:
Marine org - shark
Passive transport
• Diffusion across a membrane• Requires no energy b/c molecules moving
down concentration gradient (H to L)• 3 types
– Diffusion– Osmosis– Facilitated diffusion
Facilitated Diffusion
• Diffusion of solutes across membrane w/ help of proteins– Large polar or
ions– proteins
• Specific • Can be sat• Can be
inhibited– Protein
transports solute by• Changing
shape• Selective
channels
Cystic Fibrosis
Cystic FibrosisCause: Humans have a gene encoded in their DNA which
manufactures a special protein known as CFTR, Cystic Fibrosis Transmembrane Conductance Regulator. This protein controls the flow of chloride ions across the cell membrane.
Active TransportThe pumping of solutes against their gradient (L to H)
• Nonspontaneous
• Requires energy (usually ATP)
• Maintains steep ionic gradients (potential energy)
• Ex: Na/K pump
Active transport
Active transport
Ion pumps – pump ions across membrane– generate voltage across mem– Electrochemical gradient – combo of concentration
gradient & electrical gradient– Na/K pump is ex
Endocytosis & Exocytosis• Methods for very large molecules &
particles to get into & out of the cell• Requires energy b/c requires movement
of the plasma membrane.
http://highered.mcgraw-hill.com/olc/dl/120068/bio02.swfAnimation, baby!
Endocytosis & ExocytosisExocytosis Endocytosis
Definition Exporting macromolecules by fusion of vesicles to pm
Importing of macromolecules by forming vesicles with pm
Vesicles come from
Budded from ER or Golgi
Pm & sinks inward & pinches off into cytoplasm
Used to Secrete products - insulin
Incorporate extracellular large substances
Endocytosis
3 types:• Phagocytosis – cell “eating” solid particles
(uses pseudopodia)• Pinocytosis – cell “drinking” fluid droplets• Receptor mediated endocytosis –
importing specific macromolecules
Since cells can’t continue to grow larger, they must split, or divide at
some point.
Cell Cycle2 parts:• Interphase – period of growth & DNA synthesis
(copying)
• Mitotic phase – period of cell division (1 cell divides into 2 cells)I love
cells, baby!
Interphase – time of cell growth & copying of DNA
3 phases of interphase:
• G1 – growing & ribosomes making proteins
• S – synthesis (or copying) of DNA (sister chromatids formed)
• G2 – growing & getting ready to divide
Cells spend most of their time in interphase.
DNA is in chromatin (stringy) form.
Mitotic Phase – time of cell division Consists of 2 main phases:1. Mitosis – division of nucleus2. Cytokinesis – division of cytoplasm
Sister Chromatids• Identical copies of chromosomes attached
by a centromere.
Mitosis
4 phases:• Prophase • Metaphase• Anaphase• Telophase
http://www.cellsalive.com/mitosis.htm
Prophase
• DNA condenses into chromosomes
• Nuclear membrane disappears
• Centrioles move toward poles
• Spindle fibers form & attach to chromosomes
Metaphase
• Sister chromatids lined up on metaphase plate with spindle fibers attached to them.
Anaphase• Sister chromatids get pulled apart to poles
as spindle fibers shorten.
Telophase• New nuclear membrane forms around
chromosomes at each pole• Chromosomes “unpack” into chromatin• Cell membrane begins to pinch in (animals cells)
or cell plate develops (plant cells)
Cytokinesis – division of the cytoplasm
Cleavage furrowCell plate
Control of the Cell Cycle
• Enzymes control cell cycle so cells divide at the right times
• Cancer – uncontrolled cell division caused by a change in the DNA that codes for the making of the control enzymes
Cell Cycle Control• http://wps.prenhall.com/esm_freeman_biosc
i_1/7/1948/498717.cw/index.html
Internal Vs external signals
• Internal – the checkpoints
• External – growth factors, density dependent inhibition, anchorage dependence
cancer
• Tumor• Begign• Malignant• Metastasis• Radiation & chemo
Cancer
• Forms tumors & can spread through body - metastasize
Causes of Cancer
• Environmental factors
• UV radiation from sun
• Tobacco• Viral
infections • Genetic
How to prevent cancer:
• Low fat, high fiber diet
• Vitamins• Exercise• Don’t smoke• Use sunscreen• Regular doctor
appointments
Removal of colon polyps
• http://www.gihealth.com/flashvideo/flash.html
Review of the cell
cycle
• http://www.cellsalive.com/mitosis.htm