Exam 2 Flashcards
Skeleton vs Cytoskeleton
both: provide structural support, stability, and facilitate locomotion
The Cytoskeleton: allows for transport of material to different locations, highly dynamic (!), multiple types of structures: (actin filaments, intermediate filaments, microtubules)
Actin-Microfilaments
made up of a globular protein, actin
- polymerize vic non-covalent interactions
- final filament made up of 2 strands that coil around each other in a double helix pattern
- actin is not symmetrical (has a plus and minus end) - thus resulting filaments also have a plus and minus end (plus end added onto faster than minus end)
- dynamic: will shrink or grow depending on cellular conditions
- actin binding proteins interact with actin filaments
- tend to be located just under the plasma membrane, also linked to many cytoplasmic proteins found in cell-cell junctions
- functions: shape, contraction, membrane movements, cell division
- myosin: actin’s motor protein
Intermediate Filaments
(intermediate size)
- made up of long polymers that form cable-like structures in cells
- dont display an “endedness” or polarity
- not associated with motor proteins
- keratins: maintain cell shape + skin/fingernails/hair
- Nuclear Lamins: provide structural support for nuclear envelope
Microtubules
composed of repeating subunits made up of a heterodimer of alpha and beta tubulis (form a hollow tube that constitutes the full microtubule)
- oriented so alpha tubulin is always exposed at one end (minus end)and the beta tubule is exposed at the plus end
- originate most of the time from the microtubule organizing structure AKA centrosome - minus ends are stabilized by centrosome, plus ends grow away
- highly dynamic unless the plus end is stabilized by regulatory proteins
- functions: vesicle transport, chromosome separation, stability + structure, provide a framework for organizing the cells organelles
- Microtubule motors: dyneins + kinesins
Contents of cell membranes
lipids, proteins, carbohydrates
Lipids in cell membrane
lipid bilayer –> amphipathic
- phospholipids = primary component of membranes
*different phospholipids (different head groups and fatty acid tails) have different properties and functions
*different phospholipids are inserted into different membrane layers
- cholesterol = helps influence permeability and fluidity of membrane
*increase cholesterol –> membrane more fluid and less permeable
*decrease cholesterol –> membrane less fluid and more permeable
Proteins in cell membrane
carry out most “activities” of membranes
Lipids and proteins are held together in sheets by _____ bonds
non-covalent
“Fluid mosaic” - the non-covalently interacting lipids and proteins in a membrane can “flow” past each other within the two-dimensional membrane
Carbohydrates in the cell membrane
Most membrane carbs are “oligosaccharides” = short chain of linked monosaccharides (sugar)
- not exposed to cytosolic side of membrane
*Cytosol - area inside of cell but not inside an organele
- covalently linked to most membrane proteins and some lipids
*glycoprotein = protein with a carbohydrate attached
*glycolipid = lipid with carbohydrate attached
Is it likely that soluble macromolecules frequently pass directly across the bilayer?
Most* macromolecules (proteins, carbohydrates, nucleic acids) are large and most often polar: will not be able to enter and pass through hydrophobic center to other side of lipid bilayer
*some lipids are exceptions
ex: testosterone = sterol lipid with enough hydrophobicity to pass through membrane into cell
Characteristics of biological membranes
- molecules constantly + rapidly moving within their own layer = fluid membrane
- molecules in membrane rarely flip from 1 layer of bilayer to another
- biological membranes tends to be impermeable to:
- charged molecules: H+, Na+, K+, Ca+, Cl-
- large, polar molecules: sugars, amino acids, nucleotides
- lipid membranes are more permeable to small, uncharged (including polar) molecules (e.g. H2O) and to larger hydrophobic molecules… BUT specific charged or large, polar molecules often do cross the membranes of living cells… How? proteins!
Membrane Proteins facts
- small percentage of total molecules in cell membranes
- up to 75% of cell membrane mass consists of protein
Functions of membrane proteins
- regulated movement of specific molecules across membrane
- help provide structure
- cell-cell communication
- sensing environment (receptor proteins)
- protection
The two general types of membrane proteins
Transmembrane proteins (=integral membrane proteins) and Peripheral Membrane Proteins
Transmembrane proteins
-amphipathic: hydrophobic + hydrophilic region
transmembrane domain:
- alpha helix of 20-30 predominantly hydrophobic residues
- single pass transmembrane protein = 1 transmembrane domain
- multi-pass transmembrane protein = >1 membrane-spanning domain (several alpha helices span membrane in multi-pass transmembrane proteins
*specific proteins span the membrane with a specific orientation - allows protein to carry out specific functions at the membrane (e.g. receptor proteins)
Peripheral Membrane Proteins
interact non-covalently with surface of membrane or membrane proteins - not inserted into lipid bilayer (see thought problem on 14 sept 2022 slides)
Transport across membranes is necessary even through cell membranes act as barriers for some molecules (environment on 1 side of membrane is often not equivalent to the environment on the other (often cytosolic vs non-cytosolic)
Transport is necessary for nutrient uptake, waste excretion, and regulation of relative ion and other molecule concentrations
Membrane proteins perform ____ transport
regulated
Energy requirement for passive transport
(movement of molecules without external energy input)
Energy for movement comes from:
- gradient differences across membrane
*diffusion - spontaneous movement of a molecule down a gradient
- chemical gradient = differences in concentration
- electrical gradient = differences in charge
*membrane potential = differences in charge across a membrane
- electrochemical gradient = chemical gradient + electrical gradient
If a molecules cant pass directly through lipid bilayer, passive transport occurs through ______
channel proteins
Facilitated Diffusion
protein-mediated movement of molecules down a gradient across membrane
- channel proteins are often “gated” to only allow diffusion under certain conditions
- ligand-gated channels: open (or close) only when bound to a specific molecule
- voltage-gated channel: open (or close) in response to change in electrochemical gradient across membrane
*mot channel proteins only allow passage of specific molecules through them (eg. Na+ vs Cl- vs K+ channel)
Energy requirement for active transport
uses energy to pump molecules against an electrochemical gradient
Energy sources:
1. ATP
2. electrochemical gradient
Mechanisms of active transport
- transport protein binds solute molecule on 1 side of protein
- energy input causes conformational change in transport protein
- moves solute to other side of membrane
- reduces affinity of transporter for solute - solute is released and transporter returns to original conformation
ATP as an energy source for active transport
transporter protein functions as ATPase
(ex Na+ – K+ ATPase)
phosphorylation - covalent binding of a phosphate to a substrate - phosphorylation of a protein changes its shape and thus its activity
Electrochemical gradient as an energy source for active transport
cotransport
- free energy is released as molecules move down gradient
- released free energy is used to change protein structure to transport a 2nd molecule
Metabolism
the sum of all chemical reactions occurring within a cell
- metabolic pathways can build, break down, and alter organic molecules
Metabolic pathways
series of individual reactions where product of one is reactant for next
- often restricted to particular location within the cell
- compartmentalized - localized enzymes, substrates, etc
Anabolism
synthesis of more complex molecules
- used ATP hydrolysis or other forms of energy released couples with anabolic rxns (ex: protein synthesis)
- “constructive metabolism”
Catabolism
the degradation of organic compounds
- includes the breakdown of carbs, lipids, and proteins to release free energy
- energy is released in small, controlled rxns on slides
Redox rxns
Exchange of e- between redox pairs
Require:
1. reductant = e- donor = reducing agent
- ex: NADH releases 2e- (and 1H+) when oxidized to NAD+
2. Oxidant = e- acceptor = oxidizing agent
- ex: O2, ex: NAD+
*reductant and oxidant are always paired in redox rxns –> no free e- floating around
*shift in location of e- causes change in available free energy
- e- have high PE when associated with less EN atoms (eg C,H)
- release of high energy e- provides energy for chemical rxns (coupled rxns!)
***Redox rxns provide energy necessary for cells to carry out their functions!
Cellular respiration of glucose overview
Phase 1 of glycolysis
=1st 5 steps = initial energy input
- hydrolysis of ATP coupled with rxns with large positive Change in G generates 2 3-C molecules that can be broken down to release energy in steps
Phase 2 of glycolysis
=2nd 5 steps = energy output
Large negative change in G
*energy released is captured in ATP and NADH
Fermentation
occurs anaerobic conditions
- regeneration of NAD+ without O2
- pyruvate as e- acceptor
- lactate or ethanol is final e- acceptor to regenerate NAD+ w/out O2
a. lactic acid fermentation occurs in animals and some bacteria
Mitochondrial matrix
protein-rich regions surrounded by IMM
Citric acid cycle: the process
- Pyruvate (3c) is converted to acetyl-CoA (2C) = pyruvate processing
- NADH is generated by redox
- CO2 is released - 2C acetyl-CoA is linked to 4C Oxaloacetate to make 6C citrate
- As cycle progresses, 6C molecule is broken down into 5C, then 4C, then rearranged back to 4C Oxaloacetate
- oxidized carbons released as CO2
- some GTP (ATP) is produced
- dehydrogenase enzymes catalyze release of e-- released e- transferred to NAD+ and FAD at specific enzyme-catalyzed steps to make NADH, FADH2
Oxidative phosphorylation steps
- oxidation of NADH and FADH2 released e- = release of energy
- oxidized by complex of proteins, coenzymes, and cofactors in IMM = e- transport chain (ETC) - released e- from NADH and FADH2 enter ETC (4 separate complexes)
- e- passed along ETC in series of redox rxns
- binding and release of e- causes shape changes in proteins in ETC
- pumps H+ across IMM out of mitochondrial matrix - pumping of H+ out of matrix generates a H+ gradient across IMM
- movement of H+ down electrochemical gradient through ATP synthase releases energy
- H+ pass through channel in ATP synthase- cause conformational changes in ATP synthase enzymes
- results in phosphorylation of ADP–>ATP
*vast majority of ATP in aerobic cells is produced by ATP synthase as a result of oxidative phosphorylation
- cause conformational changes in ATP synthase enzymes
- oxygen functions as final acceptor of e- and H+ in respiration chain
- O2 becomes reduced to H2O in mitochondria
- the reason you inhale is to have O2 as an e- acceptor
