Cell Biology Exam 4 Study Guide
function of integrin proteins
-attachment of cell to EMC/signal transduction
structural features of cadherins proteins
-calcium dependent -large extracelular segment, small cytoplasmic segment, and a transmembrane domain
function of selectin proteins
-immune recognition (cell-cell binding functions in leukocytes migration and clotting) -recognizes the carbs on other cells and binds to them
selectins
-integral membrane glycoproteins that recognize and bind to specific arrangements of carbohydrate groups projecting from the surface of other cells -has a small cytoplasmic domain, a single membrane spanning unit, and a large extracellular segment has L-selectin, P-selectin, E-selectin -present in leukocytes and involved in platletes migration -binding of selectin to ligands require Ca2+
structural features of tight junctions
-integral proteins of 2 adjacent membranes meet -interconnected strands of integral proteins
function of gap junctions
-intracellular communication -sites of cell-cell communication -integrate the activities of one cell of tissue into function unit
rubisco
-large multisubunit enzyme, converts inorganic carbon to useful biological molecules; ribulose bisphosphate caroxylase oxygenase -can only fix 3 CO2 molecules per second, super slow that's why we need a lot of it
photosystem I & II
-large pigment protein complexes; PSII promotes electrons from below water to midway; PSI promotes electrons promotes electrons from midway to above NADP+
Chloroplast
-membrane bound organelle; main site of photosynthesis -found in meophyll cells -has an inner and outer membrane
function of plasmodesmata junctions
-sites of cell-cell communication in plants
stroma
-space inside chloroplast inner membrane but outside thylakoids -less acidic than the lumen -where ATP synthesis happens
function of desmosomes junctions
-used to maintain epithelial structure -sensitive to mechanical stressors
describe the structural and functional differences between LHC chlorophylls and reaction center chlorophylls
LHC: complexes of subunit proteins that join to form complexes of photosystems; Absorbs energy to donate to the Reaction Centers Reaction center: P680 or P700; • Transfers electrons to an electron acceptor (Pheophytin in PSII, and A0 in PSI)
absorption spectrum
actual wavelength that varying pigments in a molecule can absorb
major role of gap junctions
creates a connection accros a distance between cytoplasm of cells
plasmodesmata
cytoplasmic channels that connect most plant cells and extend between adjacent cells directly through the cell wall. Lined with plasma membrane and usually contain a dense central structure (desmotubule) derived from the endoplasmic reticulum of the two cells.
major role of hemidesmosome junctions
helps with cell attachment
interaction type of collagen protein
main protein interacting with the ECM
major role of tight junctions
makes it difficult for molecules to pass paracellularly
what is the relationship between the light-dependent and light-independent phases of photosynthesis in terms of chemicals that link the two
the light-dependent reactions produce NADPH and ATP which are the molecules used in the Calvin Cycle to produce the GAP -> F16bP -> sucrose
know the major roles of the individual proteins below including whether they are involved in cel-cell or cell-ECM interations: collagen fibronectin integrins catenins laminins
(see study guide)
know the major roles of the junctions below, including whether they are involved in cell-cell, cell substrate, or cell-ECM interactions: hemidesmosome tight junctions gap junction focal adhesion plasmodesmata
(see study guide)
know the unique structural features of collagen and connexins
*Collagen: 3 polypeptide alpha chains coiled around each other to form a triple helix configuration. Each of the chains has ~1000 amino acid residues. Undergo hydrogen bonding. *Connexins: four-pass transmembrane proteins with a C & N cytoplasmic terminus, a cytoplasmic loop, and two extra-cellular loops. Assembled in groups of 6 to form hemichannels. Average lenght ~380 amino acids.
light-independent reactions
- second series of reactions of photosynthesis where carbohydrates are made from CO2 using energy from ATP and NADPH -the calvin cycle
structural features of integrin proteins
-2 covalently linked glycoprotein subunits (1 alpha and 1 beta) -NH2 head
structure of gap junctions
-6 connexin=1 connexon -2 connexon = 1 gap junction
relate the absorption spectrum of a plant extract to the action spectrum of photosynthesis
-Action Spectrum -Indicates the relative efficiency with which light of various wavelengths is able to promote photosynthesis -Identifies the wavelength that are more effective in bringing about physiological response. -Absorption Spectrum -The intensity of light absorbed relative to its wavelength -Measures wavelength of light absorbed by pigment -The presence of pigments with varying absorption properties ensures that a greater percent of incoming photons will stimulate photosynthesis -The action spectrum for photosynthesis follows the absorption spectrum of chlorophylls and carotenoids fairly closely!
carotenoids (B-carotene)
-An accessory pigment in photosynthesis. Unlike chlorophyll, it is unable to do anything with the light it takes it, but it can pass along its energy. -contains a linear system of conjugated double bonds absorb light in the blue and green regions of the spectrum, so they give off orange color function as secondary light collectors, also they draw excess energy of exicted electrons and dissipates it as heat
know the variety of the 2 proteins that make up tight junctions and how they relate to tight junction differences in permeability
-Claudins and Occludins are used to make TJ's -They have many different isoforms which lead to different combinations of binding. -The amount of complexes made between the membranes by these proteins changes how selective the membrane is. -distribution of certain claudins in an area changes depending on the tissue and what its needs are
what structural features make the cholorphyll molecule a colored pigment
-Consists of porphyrin ring with magnesium ion in center -Long hydrocarbon tail -Rings = delocalization of electrons forming a cloud -Chlorophyll a is present in all oxygen-producing photosynthetic organisms. -Ring = light absorbing -Tail = keeps chlorophyll embedded in the photosynthetic membrane.
explain the circumstances for and the molecular mechanism of control of certain calvin cycle enzymes by the redox state of thioredoxin
-Ferrodoxin, which is the final acceptor of PSI, transfers electrons to NADPH, but it also transfers some to Thioredoxin. Thioredoxin reduces disulfide bridges (causing conformational change) to activate the enzymes in the Calvin Cycle. -Also, the pH of the stroma plays a role. If it is more alkaline, then the enzymes move more quickly. This would make sense in light reactions because H+ are being pulled out of the stroma and in to the thylakoids when light reactions are occuring at the PS's.
explain the operation of a light-harvesting complex, including the role of accessory pigments
-LHCII proteins bind both chlorophyll and carotenoid pigments -LCH contains chlorophylls, proteins, pigments antennas -antenna pigments absorb protons of various wavelengths and transfers energy to pigment molecules at the reaction center -accessory pigments: other pigments that increase the wavelength absorption of the chlorophyll molecule (carotenoids, chlorophyll b)
what determines the absorption spectrum of a pigment
-Pigments only absorb light at a particular wavelength -Alternating single and double bonds along porphyrin ring -Conjugation = strong absorbers of light -Conjugation broadens absorption peaks and increases the range of wavelength -Absorbed energy causes a redistribution of electron density of the molecule -Loss of electron to its electron acceptor
explain the mechanism of photolysis: starting with oxidation of P680; explain the mechanism of its reduction by the oxygen complex adn the subsequent oxidation of water to O2
-The overall reaction is 2e + PQ + 2H -> PQH2 (Happens twice) Steps 1. Photons come in and excite an electron in P680, which is in PSII 2. The electron is transferred to Pheophytin and P680 is oxidized to P680+ 3. P680+ is so strong that it pulls electrons from water 4. The electrons from the water are found in the Oxygen Evolving Complex (MnCa cluster involved here) 5. An intermediate tyrosine carries the electrons to the P680+ 6. Water splits up and P680+ is reduced back to P680 7. The process repeats, and overall it takes 4 photons to make the reaction go as described
visible light
-a form of electromagnetic radiation...the wavelenght ranges that are visible to our eyes... -the visible spectrum ranges from 350nm to 750nm
fibronectin
-a glycoprotein that binds to integrins. -Binds collagen. -Helps in cell adhesion/maintaining the structure of extracellular matrix.
hemidesmosome
-adhesive structure at basal surface of epithelial cells, contains dense plaque on inner surface of plasma membrane with keratin containing filaments extending into the cytoplasm -the signals transmitted from the ECM affect the shape and activity of the cell
focal adhesions
-adhesive structures containing integrins in the region the plasma membrane portion of the integrins are connected by various adaptive proteins -they are sensory structures that collect information about physical and chemical properties in the env. can create mechanical forces
describe the functions of plastmodesmata
-allow cell communication between plant cell walls they are cytoplasmic channels that pass through teh cell walls of adjacent cells -lined by plasma membrane and contain a dense central structure (desmotubule) -cell-cell communication as substances pass through the annulus surrounding the desmotubule
function of tight junctions
-barrier to free diffusion of water and solutes -helps maintain polarity of cells -different permeabilities
light harvesting complex I and II
-bind chlorophylls and carotenoids and are situated outside the core of the photosystems -the excitation energy is passed from the anetenna pigment in the light harvesting complex to the chlorophyll molecule in PSII, then from there to the PSII reaction center.
P700
-chlorophyll dimer known as photosystem I present in the reaction center, once it receives the excitation energy it transfers an electron to the molecule A0 (aka chlorophyll a)
P680
-chlorophyll dimer known as photosystem II a reaction center pigment that gets the excitation energy from chlorophyll molecule and responds by transferring a single electron to pheophytin
photosynthesis
-converts sunlight to chemical energy that can be used chemical energy produced is stored in the form of carbohydrates -in the process, low energy electrons are removed from -a donor and converted into high energy electrons using light energy
structure of plasmodesmata junctions
-cytoplasmic channels -lined by plasma membrane -dense central structure derived by ER of the two cells
wavelength
-distance between two wave crests -as the wavelength increases, the energy decreases so longer wavelengths have lower energy
cadherins
-family of glycoproteins that mediate Ca2+ dependent cell-cell adhesion -transmit signals from ECM to cytoplasm -they join cells to one another by binding to the cadherin on that cell
phenophytin
-first electron carrier in PSII -a primary electron acceptor, it receives electrons from P680 and transfers them to plastiquinone
light-dependent reactions
-first series of reactions of photosynthesis where sunlight energy is converted to chemical energy stored as ATP and NADPH -occurs in the thylakoid membrane
thylakoid
-flattened, membranous sacs inside the chloroplast; have machinery for photosynthesis -place within the thylakoid is called lumen -the place outside the thylakoid but within the chloroplast membrane is called the stroma
function of cadherin proteins
-form adherin binding sites
know the size (and molecular weight) selectivity of gap junctions
-mammalian gap junctions allow the diffusion of molecules having a molecular mass below approx. 1000 daltons (1 kDa) -relatively nonselective -gated: -closure probably triggered by phosphorylation of connexin subunits -closure also triggered by voltage changes across the junction or abnormaly high Ca+ cytosolic concentrations
excited state
-molecule with a promoted electron following photon absorption -when light is absorbed, the electron gets pushed from the inner to the outer orbital
tight junctions
-occur at apical end of junctional complexes between adjacent epithelial cells; adjoining membranes make contact at intermittent points where integral proteins of two adjacent membranes meet
structural features of adherens junctions
-occur in belts hat encircle each of the cells -cells are held together by Ca dependent linkages formed by the extracellular domains of cadherins proteins
describe the molecular weight selectivity of plasmodesmata
-recent studies suggest that plasmodesmata allow much larger molecules 50,000 daltons (up to 50 kDa) through -plasmodesmata is capable of dilation -plants produce their own movement proteins that regulate the flow of proteins and RNAs from cell to cell allowing for the dilation of the plasmodesmata
describe what is known (from the text) about regulation of opening of gap junctions
-regulation differs depending on the specific connexins forming the connexon -in some cases, connexons in neighboring cells that are composed of different connexins are able to dock, but not in other cases -compatibility differences: promoting or preventing communication between types of cells
structural features of selectins protein
-single pass -calcium dependent -N terminus on the outside -EGF sequence -large extracellular domain and a small cytoplasmic domain
adherens junctions
-specialized adhesive junctions common in epithelia. -The plasma membranes in this region are separated by 20-35 nm and are sites where cadherin molecules are concentrated. The cells are held together by linkages between the extracellular domains of cadherin molecules that bridge the gap between neighboring cells.
major role of laminin proteins
-stimulates mammary cells -by binding to the cell surface integrins and activating the kinases they are connected to on the inside
NADPH
Electron carrier that is very similar to NADH. It is created in the light dependent part of photosynthesis, and then it is used in the Calvin cycle which makes glucose.
know the epithelial location of tight junctions and their functions in those issues
Locations: Skin, lining of arteries, lining of organs Function: Retention of certain molecules. Skin for pretty much everything, arteries so the blood actually gets places, and organs to make sure that the stomach doesn't burn up everything and whatnot -keep molecules from passing paracellularly
primary electron acceptor
Molecule that receives the photoexcited electron from reaction-center pigments in both photosystems.
connexins/connexons
Multisubunit complex of a gap junction formed from the clustering within the plasma membrane of an integral membrane protein called connexin. Each connexon is composed of six connexin subunits arranged around a central opening (annulus).
describe the structural and function differences between P680 and P700
P680: • Reaction center of PSII • 680 = wavelength absorbed most strongly • Excites electron • Electron transferred to pheophytin P700: • Reaction enter of PSI • 700 = wavelength absorbed most strongly • Excites electron • Electrons transferred to A0 • A0 = very strong reducing agent
describe the structural and functional differences between PSI and PSII
PSI: Has Ferrorodoxin used to reduce NADP+ to NADPH • Reduces molecule of NADP to NADPH PSII: Has the Oxygen Evolving Center for Photolysis • Catalyzes the light driven oxidation of water • Catalyzes the transfer of electrons from H20 → Plastoquinone (PQ) • Major contributor in forming H+ gradient.
what are the starting and ending carbon-containing molecules of the Calvin Cycle
Start: RbuP and CO2 End: Glucose/Sucrose/Fructose and RbuP (takes 6 cycles to completely make glucose)
cellulose microfibrils
a fiber made up of celluose. These microfibrils are laid down in the inner surface of the primary cell wall (cell absorbs water=increase volume=separation of existing microfibrils & new ones form to help increase cell strenght)
laminin
a protein of the extracellular matrix.Active part of basal lamina (helps with cell differentiation)
major role of plasmodesmata junctions
allows plant cells to pass molecules through without having to deal with the cell
occludins/claudins
an integral plasma membrane protein located at tight junctions (helps with tight junction stability/ barrier function) -not all TJs have occludins, but they have claudins
major roles of fibronectins proteins
binding for parts of the ECM to create a network -binds to the cell surface to hold ECM in stable attachment to the cell -attaches cells to the ECM
interaction type of focal adhesion junctions
cell substrate/ECM
interaction type of fibronectins proteins
cell-ECM
interaction type of hemidesmosome junctions
cell-ECM
interaction type of integrin proteins
cell-ECM (Ca+ dependent)
interaction type in gap junctions
cell-cell
interaction type in tight junctions
cell-cell
interaction type of catenins proteins
cell-cell
interaction type in plasmodesmata junctions
cell-cell (plants)
pigments
compounds that appear colored because the only absorb light of one wavelength
porphyrin ring
conjugate acids of ligands that bind metals to form complexes (one example is heme (cofactor of hemoglobin))
major role of the catenins proteins
connects cadherins to the cytoskeleton
gap junctions
connects the cytoplasm of two cells (allowing different molecules/ions to pass through a regulated gate (spanned by connexons) between cells).
major role of integrin proteins
connects to the extracellular matrix by going through the membrane -cell signalling (binding ligands and influencing events within the cell)
electromagnetic spectrum
contains all possible frequencies of electromagnetic radiation (radio waves (long wavelenght/low frequency)->Gamma Rays (short wavelenght, high frequency)....
desmosomes
disk-shaped adhesion junctions found in epithelia basal to the adherens junction
action spectrum of photosynthesis
effective wavelengths for photosynthetic reactions to occur because not all pigments in a plant do photosynthesis
reaction center
energy jumps from pigment to pigment until it arrives at the reaction center. An electron acceptor traps a light excited electron from the reaction center chlorophyll (the single chlorophyll molecule that actually transfers electrons to an e- acceptor)
interaction type of laminins proteins
extracellular glycoproteins that influences the cells around it -cell-cell
integrins
family of integral membrane proteins that bind extracellular molecules
collagen
fibrous glycoprotein known for high tensile strength
non-cyclic photophosphorylation
formation of ATP during oxygenic photosynthesis, electrons move from linearly from H2O to NADP+
chlorophyll
light absorbing photosynthetic pigment
extracellular matrix
organized network of of extracellular materials present beyond the plasma membrane; may determine shape and activity of cell
photon
packet of light energy
Calvin cycle
path converting CO2 to carbohydrate happens in the stroma
cyclic photophosphotylation
process carried out by PSI independent of PSII
proteoglycan
protein polysaccaride complex with protein core and attached glycosaminoglycans; can bind cations, which draws in water; form porous hydrated gel
major role of collagen protein
provides structural stability of the cell
function of adherens junctions
signal transduction
structural features of desmosomes junctions
specialized rope-like cadherins that create a disk shaped connection
photolysis
splitting of water during photosynthesis the process that produces O2 in plants
granum
stack of thylakoids in chloroplast
ground state
unexcited state of an atom or molecule
major role of focal adhesion junctions
used for in vitro studies (locomotion)