review topic 2
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Review Topic 2. Cell membrane defines cell. Cell membrane separates living cell from aqueous environment thin barrier = 8nm thick Controls traffic in & out of the cell allows some substances to cross more easily than others hydrophobic (nonpolar) vs. hydrophilic (polar). - PowerPoint PPT PresentationTRANSCRIPT
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Review Topic 2
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Cell membrane defines cell
• Cell membrane separates living cell from aqueous environment– thin barrier = 8nm thick
• Controls traffic in & out of the cell– allows some substances to cross more easily
than others• hydrophobic (nonpolar) vs. hydrophilic (polar)
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Many Functions of Membrane ProteinsOutside
Plasmamembrane
InsideTransporter Cell surface
receptorEnzymeactivity
Cell surface identity marker
Attachment to thecytoskeleton
Cell adhesion
“Antigen”
“Channel”
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Membrane carbohydrates
• Play a key role in cell-cell recognition– ability of a cell to distinguish one cell from
another• antigens
– important in organ & tissue development
– basis for rejection of foreign cells by immune system
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Simple Diffusion
• Move from HIGH to LOW concentration– “passive transport”– no energy needed
diffusion osmosis
movement of water
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Facilitated Diffusion
• Diffusion through protein channels– channels move specific molecules across
cell membrane– no energy needed
“The Bouncer”“The Bouncer”
open channel = fast transport
facilitated = with help
HIGH
LOW
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Concentration of water
• Direction of osmosis is determined by comparing total solute concentrations
– Hypertonic - more solute, less water, low water potential
– Hypotonic - less solute, more water, high water potential
– Isotonic - equal solute, equal water
hypotonic hypertonic
water
net movement of water
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freshwater balanced saltwater
Managing water balance
• Cell survival depends on balancing water uptake & loss
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Aquaporins
• Water moves rapidly into & out of cells– evidence that there were water channels
• protein channels allowing flow of water across cell membrane
1991 | 2003
Peter AgreJohn Hopkins
Roderick MacKinnonRockefeller
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Cell (compared to beaker) hypertonic or hypotonic
Beaker (compared to cell) hypertonic or hypotonic
Which way does the water flow? in or out of cell
.05 M .03 M
Do you understand Osmosis…
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Active Transport
“The Doorman”“The Doorman”
conformational change
• Cells may need to move molecules against concentration gradient– conformational shape change transports solute from
one side of membrane to other – protein “pump”– “costs” energy = ATP
ATP
LOW
HIGH
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Endocytosis
phagocytosis
pinocytosis
receptor-mediated endocytosis
fuse with lysosome for digestion
non-specificprocess
triggered bymolecular signal
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Enzymes vocabularysubstrate
• reactant which binds to enzyme• enzyme-substrate complex: temporary association
product • end result of reaction
active site • enzyme’s catalytic site; substrate fits into active site
substrate
enzyme
productsactive site
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Properties of enzymes
• Reaction specific– each enzyme works with a specific substrate
• chemical fit between active site & substrate– H bonds & ionic bonds
• Not consumed in reaction– single enzyme molecule can catalyze thousands
or more reactions per second• enzymes unaffected by the reaction
• Affected by cellular conditions– any condition that affects protein structure
• temperature, pH, salinity
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Induced fit model
• More accurate model of enzyme action– 3-D structure of enzyme fits substrate– substrate binding cause enzyme to change
shape leading to a tighter fit • “conformational change”• bring chemical groups in position to catalyze
reaction
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Protein denaturation
• Unfolding a protein– conditions that disrupt H bonds, ionic bonds,
disulfide bridges• temperature• pH• salinity
– alter 2° & 3° structure• alter 3-D shape
– destroys functionality• some proteins can return to their functional shape
after denaturation, many cannot
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Enzyme concentration
enzyme concentration
reac
tio
n r
ate
What’shappening here?!
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Substrate concentration
substrate concentration
reac
tio
n r
ate
What’shappening here?!
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37°
Temperature
temperature
reac
tio
n r
ate
What’shappening here?!
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7
pH
pH
reac
tio
n r
ate
20 1 3 4 5 6 8 9 10
pepsin trypsin
What’shappening here?!
11 12 13 14
pepsin
trypsin
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Salinity
salt concentration
reac
tio
n r
ate
What’shappening here?!
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Compounds which help enzymes• Activators
– cofactors • non-protein, small inorganic
compounds & ions– Mg, K, Ca, Zn, Fe, Cu– bound within enzyme molecule
– coenzymes• non-protein, organic molecules
– bind temporarily or permanently toenzyme near active site
• many vitamins– NAD (niacin; B3)– FAD (riboflavin; B2)– Coenzyme A
Mg inchlorophyll
Fe inhemoglobin
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Compounds which regulate enzymes• Inhibitors
– molecules that reduce enzyme activity– competitive inhibition– noncompetitive inhibition– irreversible inhibition– feedback inhibition
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Allosteric regulation
• Conformational changes by regulatory molecules – inhibitors
• keeps enzyme in inactive form
– activators • keeps enzyme in active form
Conformational changes Allosteric regulation
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Cooperativity
• Substrate acts as an activator– substrate causes conformational
change in enzyme• induced fit
– favors binding of substrate at 2nd site– makes enzyme more active & effective
• hemoglobinHemoglobin 4 polypeptide chains can bind 4 O2; 1st O2 binds now easier for other
3 O2 to bind
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Feedback inhibition
• Example– synthesis of amino
acid, isoleucine from amino acid, threonine
– isoleucine becomes the allosteric inhibitor of the first step in the pathway
• as product accumulates it collides with enzyme more often than substrate does
threonine
isoleucine
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Interphase
• 90% of cell life cycle– cell doing its “everyday job”
• produce RNA, synthesize proteins/enzymes
– prepares for duplication if triggered
I’m working here!
Time to divide& multiply!
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Prophase
• Chromatin condenses – visible chromosomes
• chromatids
• Centrioles move to opposite poles of cell – animal cell
• Protein fibers cross cell to form mitotic spindle– microtubules
• actin, myosin
– coordinates movement of chromosomes
• Nucleolus disappears• Nuclear membrane breaks down
green = key features
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Transition to Metaphase
• Prometaphase– spindle fibers attach to
centromeres • creating kinetochores
– microtubules attach at kinetochores
• connect centromeres to centrioles
– chromosomes begin moving
green = key features
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Metaphase
• Chromosomes align along middle of cell– metaphase plate
• meta = middle
– spindle fibers coordinate movement
– helps to ensure chromosomes separate properly
• so each new nucleus receives only 1 copy of each chromosome
green = key features
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Anaphase
• Sister chromatids separate at kinetochores – move to opposite poles
– pulled at centromeres
– pulled by motor proteins “walking”along microtubules
• actin, myosin• increased production of
ATP by mitochondria
• Poles move farther apart– polar microtubules lengthen
green = key features
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Telophase
• Chromosomes arrive at opposite poles– daughter nuclei form – nucleoli form– chromosomes disperse
• no longer visible under light microscope
• Spindle fibers disperse• Cytokinesis begins
– cell division
green = key features
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Cytokinesis
• Animals– constriction belt of actin
microfilaments around equator of cell
• cleavage furrow forms• splits cell in two• like tightening a draw
string
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Cytokinesis in Plants
• Plants– cell plate forms
• vesicles line up at equator
– derived from Golgi
• vesicles fuse to form 2 cell membranes
– new cell wall laid down between membranes
• new cell wall fuses with existing cell wall