Class test 2 Flashcards
What do membranes do?
Provide the structural basis for metabolic order. Each membrane has its own proteins and precsise enzymatic solution and functions.
what are the functions of the plasma membrane?
-Seperates living cells from their surroundings
- Maintains a constantly controlled intracellular environment
- Selectively permeable (takes up required substances and disposes of unwanted wastes)
What makes up the plasma membrane?
- phospholipid bilayer
- proteins
- steroid lipids
What is characterisitic of the phospholipid bilayer structure
It is ampiphatic: Both hydrophboic and hydrophilic
- Hydrophilic head is made of phosphate group
- Hydrophobic tails made of fatty acid chains
define selective permeability
- the plasma membrane allows some substances to cross more easily than others and blocks passage of somesubstances completley. Type of transport used depends on the type of molecule looking to cross
What is a factor of membrane fluidity?
- depends on the lipid components (staurated or unsaturated hydrocarbons)
- in a living cell, the bilayer has the consistency of salad oil. at lower temperatures, it is more rigid and the motion of the datty chains slow down
define homeoviscous adaptation
when the temperature goes down, the proportion of unsaturated fatty acids goes up and the membrane stays fluid
the longer the fatty acid chains…
the less fluid the membrane is likely to be
what steroid has an effect on plasma mebrane fluidity?
- chloesterol
at high temps, cholesterol stabalizes the membrane, the polar OH groups on cholesterol bind to the phosphate groups pf the phospholipid which restricts its motion. AT low temps, it acts as a spacer between the chain which prevent van der waals interaction.
There are two types of membrane proteins, what are they?
- integral proteins: firmly bound to the membrane, penetrating the core of the lipid bilayer
- ampiphatic (hydrophilic region extends out of the cell, hydrophobic regions inereact with the fatty acid tails)
- some doe not extend fully through the membrane (transmembrane proteins)
- examples are aquaproteins (allow water in and out of the cell) and glycoproteins - peripheral proteins: not embedded in the lipid bilayer. They are located on the inner and outer surface of the membrane
- may be receptors of the cell or enzymes associated with the inner membrane
why is it said that the bilayer is asymmetric?
- there are more protiens attached to one side more than the other
- each side of the membrane has specific characterisitics due to the types of porteins attached
- proteins are asymmetrically oriened, this is produced by the specific way every protein is inserted in the bilayer
how are plasma membrane proteins made?
- peripheral proteins are made byfree ribosomes in the cytoplasm
-integral proteins are made by the ribosomes embedded in the rough ER
what are the 6 main functions of membrane proteins?
- transport
- enzymatic activity
- signal transduction
- cell-to-cell recognition
- intercellular joining
- attachement to the cytoskeleton and ECM
what is the point of cell-to-cell recognition ?
- provides identifucation tags to cells, allows them to be distinguisged among other cells.
what happens when the body lacks cell-to-cell recognition?
- when antiobodies fail to recognize what cells are not freign to our body, the body is said to suffer from an autoimmune disease
ex; rhumatoid arthritis, MS
what is the point of intercellular joining?
allow cells to communicate and forms barriers
-ex: plant cell junctions like the plasmodesmata allows for communication between cells
what is the plasmodesmata ?
- channels that allow rapid chemical communication and sharing of materials between plant cells
- not only ridge the plasma membrane of adjacent cells, but alos their cell walls
what are desmosomes
IN ANIMALS
- attach animla cells to eachother or the ECM without inhibiting the passage of materials between cells.
- very strong
why dont plants have desmosomes
THE REASON WHY PLANTS CELLS DONT HAVE DESMOSOMES IS BECAUSE THEY HAVE A CELL WALL FOR STRENGTH
how do desmosomes fucntion
- dsmosomes have a pair of button-like discs that bind to the cytosolic side of the plasma membrane of adjacent cells and the intercellular protein filaments that connect them
- the intermediate filaments in the cells are attached to the discs and are connected to toher desmosomes
-the intermediate filaments of adjacent cells are therefore connected, so mechanical stresses are districuted throughou the tissue
what are tight junctions
form of interceullar joining that is so tight it prevents substances from leaking between them
- proteins that form tight junctions hold the cells together in actual physical contact, forming a sheet of tissue
ex: tight junctions are often found in the stomach to avoid strong acids from injuring nearby organs and tissues
what are gap juncitons
intercellular joining that bridge the space between animal cells like desmosomes, but the space they span is narrower. contain channels that conect the cytoplasm of adjacent cells, allowing communication
ex: these allow for elctrical communication between animal cells (gap junction in heart permit the flow of ions to synchronize contractions)
what is the point of the attachement of the cytoplasm to the ECM ?
- some proteins do not move freely within the plasma membrane they are fixed and help keep the membrane in place
- these proteins are non-covalently bonded to the cytoskeleton and to fibers of the adjacent ECM
what is the ECM?
ECM is made of extracellular fluid, a gel-like substance made of carb and fibrous proteins
- the most prominent protein is collagen
- fibronectins (glycoprotein) heps organize the matrix and also aid cells in attaching to the matrix by binding to proteins that extend from the plasma membrane
fibronectins bind to…
integrins: integral transmembrane proteins that serve as memrane receptors, play a roll in cell movement and oranizing the cytoskeleton, and anchor the ECM to the microfilaments of the internal cytoskeleton
what are some determining factors for why a molecule can or cannot pass through a given membrane
- size
-polarity
T or F: large molecules can cross through both the membrane proteins and the phospholipid bilayer
F, ONLY membrane proteins
T or F: Large quanaties can be imported or removed from the cell through vesicles as a form of bulk transoort
trueee
what are the two ways molecules can leave or enter cells?
- passive transport (NO ATP REQUIRED)
a) diffusion
- substances move from an area of high conc. to low conc. until there is an equilibrium
b) osmosis (water only)
- diffusion of water across a selectively permeable membrane (low solute to high solute, IMPERMEABLE SOLUTES ONLY)
c) facilitated diffusion
-transport proteins speed up the passive movement of molecules across the membrane
-channel proteins provide hydrophilic corrdiors that allow specific molecules to cross the membrane (usually gated)
- carrier proteins undergoa shape change when binding to a solute that wants to enter, slower than channel proteins (rate depdns on the no. of carriers in the membrane)
(requires integral membrane protein) - Active transport (REQUIRES ATP): moves substances against their conc. gradient, done by integral proteins that require ATP
a) transporter pumps
(PRIMARY AND SECONDARY ACTIVE TRANSPORT)
b) bulk transport (endocytosis and exocytosis)
- large molecules cannot cross the membrane using any other transportation method, so they use bulk transport
define the net movement of molecules
movement in one direction minus the movement in the opposing direction
- net movement will be in direction of the conc. gradient
- at equilibrium, the net movement is zero, but exchane still occurs on a molecule-for-molecules basis
define osmotic pressure
the hydrostatic pressure needed to stop the net flow of water across a membrane due to osmosis
High solute conc = high osmotic pressure
low solute conc= low osmostic pressure
define tonicity
ability of a solution to cause a cell to gain or lose water
define…
isotonic solution
hypertonic solution
hypotinic solution
isotonic: solute conc. in the solution is the same as the inside of the cell
- no net water movement across the plasma membrane
hypertonic solution: solute conc. in the solutions is larger than the inside of the cell
-cell loses water
hypotonic solution: solution conc. in the solution is smaller than that inside cell
-cell gains water
tonicity depends on….
the total conc. of impermeable solutes
how do we observe tonicity in plant cells (hypo, iso, hyper)
hypo: turgor pressure, cell is turgif, everything is up and good
iso: water vacuole does not exert enough pressure on cell wall to give proper support
hypertonic: water seeks to exit cell but cell wall cannot help in this case..everything droops
define osmolarity
the total conc of all solutes, mesaured in osmoles
define
iso-osmotic
hyper-osmotic
hypo-osmotic
iso-osmotic: number of particles are = on either side of the membrane
hyper-osmotic: no. of particles in the hypoerosmotic solution is higher than across the membrane
hypo-osmotic: the no. of particles in the hypo-osmotic solution is lower than across the membrane
define osmoregulation
the control of water balance
look over an osmosis problem rn
live
what are the 3 types of carrier proteins
uniporters, aymporters, antiporters
what are the two types of ACTIVE TRANSPORT
- primary active transport
- carrier- mediated
- energy provided by ATP (donation of phsophate group to a carrier protein, allowin for the passage of substances across the membrane) - secondary active transport: the use of an exisiting gradient to drive the active transport of a solute
- pumps produce electrochemical gradients that store energy for cellular work
- co-transport
- ATP required
- Ion gradient as a mean of transport
what is the main diff between active and passive transport
passive: high to low conc. always
- no atp
- passive transport using a channel is facilitated diffusion
active: always against the gradient
- uses atp
- can be large or small molecules
requires carrier/transport protein
- allows cell to maintain diff internal and external environments
what are the steps of primary active transport Na+/K+ ATPase Ion pump
- 3 cytoplasmic Na+ binds to the sodium potassium pump. the affinity for Na+ is high when the protein has this shape
- Na+ binding stimulates phosphorylation by ATP
- Phosphorylation leads to a change in ATP shape, reducing its affinity for Na+, which is released outside of the cell
- The new shape has an affinity for two K+, which binds to on the extracellular side and triggers release of the phosphate group
- Loss of the phosphate gorup restores the protein’s original shape, which has a lower affinity for K+
- K+ is release into the cell, affinity for Na+ is high again, the cycle persists
define membrane potential. what generates it?
membrane potential: voltage difference across a membrane. the voltage is created by the differences in the distribution of +ve and -ve ions across a plasma membrane
generated by ion pumps that cause a charge difference.
i.e. extracting +ve ions from the inside of the cell wall would create a net charge across the membrane (more +ve outside than in)
define electrogenic pump
pumps that are transport proteins that generate a voltage across a membrane
T or F -ve charge trapped inside the cell also contribute to membrane potential
T
the result of Na+/K+ ATPase favors the passive transport of ____ into the cell and ______ out of the cell via ion channels
cations, anions
active transport creates… this creates …..
- an electrical gradient where there is different net charge insode and outside of the cell
- a conc. gradient
THIS CREATES AN ELECTROCHEMICAL GRADIENT WHICH DRIVE THINGS SUCH AS CELLULAR RESPIRATION, TRANSMISSION OF NERVE IMPULSES AND MUSCLE CONTRACTION
what is an example of secondary active transport in plants and in animals?
plants : they use atp to pump h+ against its radient out of the cell and the h+ gradient is couples to the transport of sucrose into the cell
humans: glucose is co-transported into intestinal epithelial cells (where glu conc is high) with Na+ as it moves down the gradient created by the Na+/K+ pump
in terms of bulk transport, what is exocytosis and endocytosis
exocytosis: when vesicles leave the cell
- vesicle fuses with plasma membrane and releases contents into extracellular space
- membrane proteins and phospholipids are incorporated into plasma membrane by exocytosis
-can be regulated (done as a signal response) or contructive
endocytosis: when vesicles enter the cell
ENDOCYTOSIS
define
phagocytosis
pinocytosis
receptor-mediated endocytosis
phagocytosis: large particles engulfed into vacuole which fuses with lysosome
pinocytosis: nonspecific uptake of cellular fluid
receptor-mediated endocytosis: triggered by binding of ligand to surface receptor
define receptor-mediated endocytosis & mention its characterisitcs
- a vesicle is formed through recruitment when specific molecules attach to their respective surface receptors on the membrane
- once in the molecules exit the vesicle, the receptors are returned to the cell surface for reuse
- most blood choleterol travels in lipoprotein particles
- LFL contains cholesterol destined for uptake by cells
- calls take in LDLs via receptor-mediared endocytosis, LDLs bind to specific surface receptors
T or F most cell to cell communications are chemically based
T
what is the differecne between long and local distance singalling (types of intercellular joining)
the cells that comprise a multicellular organism must be able to communicate with one another. This is largely achieved thorugh release of chemical messengers
local
- through cell junctions, cell surface molecules, paracrine singalling, synaptic signalling
long
endocrine
read slides 9-14 of lecture 9
ugh
there are 3 stages of cell signaling
- reception
signaliing molecule bind to a receptor protein located at the target cell’s surface or inside the cell
- causes a change in the shape of the receptor protein, activiating it, which allows it ot interact with molecules in the cytoplasm of the cell - transduction (activated by the binding of receptor on the cell surface)
- converts the signal form reception to a form that can bring about a specific cellular response
- can occur in a single step but usually happens in several (a signal transduction pathway. The molecules in the pathway are called relay molecules)
TRANSDUCTION AMPLIFIES THE RESPONSE (usually involves phosphorylation and dephosphorylation) - response
- the response maybe almost any cellular activity(e.g.catalysis by an enzyme) - signal deactivation
- cells have automatic and rapid mechanisms for signal deactivation:signal is no longer produced’,
Removal from receptors, protein deactivation
what are the two types of signalling molecules
water soluble
- amino-acid based
- hydrophilic
-cannot diffuse through PMs of target cells
and lipid soluble molecules
Lipid soluble
-steroids and thyroid hormones
-Hydrophobic
- can diffuse through plasma membrane of target cells
Name the two signalling mechanisms
1 cell surface signalling/cell surface receptor-mediated signalling
- water soluble signalling molecules cannot pass through the phospholipid bilayer and therefore bind to receptors on the surface of the cell
- the conversion of an extracellular chemical signal into and intracellular response
2 intracellular signalling
— can pass through the phospholipid bilayer and bind to receptors in the cytoplasm or nucleus of the target cell
- these signalling molecules will be directly involved in gene expression
- activates transcription factors
T or F when a signalling molecule binds to a receptor the receptor does not change shape
F
How can the activation of a protein receptor change cell activity?
- performing an enzymatic function within the cytoplasm
- allowing passage of molecules into or out of the cell
- initiating a transduction cascade
What are the two types of cell surface receptors ?
- G protein-couples receptors (GPCRs)
- receptor tyrosine kinases
What do we know about GPCRS
- large family of receptors found in every human cell
- all GPCRS are composed of 7 transmembrane alpha-helices joined by intracellular and extracellular loops
-Different GPCRS bind to different ligands based on the specific conformation of their active site. Differences in their cytoplasmic conformation also confer them specificity for specific G proteins - G proteins are a family of transduction proteins with variability in their specific amino acid sequence
- upon ligand binding the GPCR will change shape which initiates an intracellular signalling cascade
What are the steps of a GPCR chemical signalling ?
G proteins are peripheral membrane proteins that act as an on/off switch depending on if GTP or GDP is bound to them (GDP IS ACTIVE! GTPNIS ACTIVE). GPCRS and G proteins work with enzymes
1. When a G protein binds to the ligand the shape of the GPCR changes! Allowing its cytoplasmic portion to interact with a G protein and replace the GDP for GTP! Activating the G protein
2. Activated G protein then dissociate from the GPCR and diffuse along the PM until they find an enzyme. The enzyme then activates and triggers the next step of cellular response
3. G proteins then hydrolyze their GTP back to GDP, inactivating themselves
What do we know about receptor tyrosine kinases RTKs
- receptors that also have enzymatic activities (kinase enzymes)
- catalyze the transfer of a phosphate group
-specific to tyrosine residues - phosphate group is taken from ATP molecules
RTK WILL OFTEN INITIATE ONE PATHWAY AT THE SAME TIME IN THE CELL (KEY DIFFERENCE BETWEEN RTKS AND GPCRS)
-this regulates and coordinates cell growth and reproduction
What are the steps of RTK signalling
- RTKs are inserted into the PM by an alpha-helix domain. Their cytoplasmic domain contains multiple tyrosine amino acid residues
- When a ligand binds, the extracellular active site of a monomer, it gains a higher affinity for other monomer RTKs bound to a ligand and they dimerize. The RTK are now in a dimer complex
- Dimerization activates the tyrosine kinase region of each monomer. Each RTK then adds a P group from an ATP molecule to a tyrosine on the tail of the outer monomer.
R. RTKs are recognized by specific proteins which bind to specific phosphorylated tyrosine residues. Binding alters the effector proteins’ conformation and each protein is now able to trigger a specific signal transduction pathway = cellular response
Define dimerize
Formation of a dimer (a molecule composed of two identical, simpler molecules.
a polymer derived from two identical monomers.)
What do we know about intracellular signalling
- lipid soluble hormones can pass directly through the phospholipid bilayer of cells.
- once in the cell they bind to a specific receptor in the cytoplasm or nucleus of the cell.
- hormone-receptor complexes will go on to alter gene expression levels in the cell (up and down regulated)
What does phosphorylation involve
The transfer of the terminal phosphate group from ATP to a protein molecule.
- phosphorylation activates the protein through the induction of a conformational change (MENTIONED MUKTIPLE TIMES)
- ATP is a high energy molecule containing 3 phosphate groups and is often used
True or false: all steps of a transduction pathways involve proteins
False. Sometimes a second messenger will be used that is a smal water-soluble molecule such as cyclic amp (camp) or calcium ions (Ca2+)
How is camp made?
His made by removing 2 phosphates from ATP by adenylyl cyclase (enzyme) this is a common second messenger
Where ave calcium ions kept in the cell
They are mostly found in the smooth ER AND mitochondria ( compared to the cytosol)
If a chemical messenger has no receptor to bind,…
No response can be processed by the cell
What are the two types of responses to cell-to-cell signalling?
- nuclear: a change in which genes are expressed
(Slow)
2.cytoplasmic:activate/deactivate target protein already in cell (fast)
What does the response to a signallingmolecule depend on?
The type of receptor and or moleculesinvolved in the cascade within the target cell.
Give 3 examples of the importance of cell signalling
A. Apoptosis(cell suicide)
B. Cell division
- abnormal cell signalling in cell division can lead to
Cancer.
A) positive regulators (kinases) of the cell cycle
May be over-activated(oncogenic)
B)negative regulators(tumor suppressors),may be
Deactivated
C.Maintenance of homeostasis
Abnormal cell signalling leads to various disorders and diseases
Watch this video
https://www.youtube.com/watch?v=FkkK5lTmBYQ
The body generates ATP via organic molecules using three processes. Which ones?
- Glycolysis with fermentation
- Aerobic cellular respiration
- Anaerobic cellular respiration
What is glycolysis with fermentation
A process in which organic compounds (e.g. Monosaccharides) are incompletely broken down to produce a few ATP under anaerobic conditions (without oxygen)
What are the two types of glycolysis with fermentation
- Alcohol fermentation
- produces ethanol and organic acids
- performed by many bacteria under anaerobic conditions - Lactic acid fermentation
- produces lactate
- performed by certain fungi, some bacteria, and animals under anaerobic conditions.
What is the differences between aerobic and anaerobic cellular respiration
Aerobic
- uses 02 in the breakdown of glucose to produce
A large quantity of ATP
- used by eukaryotes and certain prokaryotes
- most efficient catabolic pathway
Anaerobic
-Uses molecules such as nitrate or sulfate instead of oxygen to breakdown glucoseto produce a large quantity of ATP
- used by certain prokaryotes.
Tor f: carbs, fats, and proteins from food can all be processed and consumed as fuel.
If so., state the formula
T
Organic compounds +o2+ADP+Pi = co2+h2o+energy (ATP and heat)
What is the most common molecule fer cellular respiration? State the formula
- Glucose
CO2H12O6+6O2+ADP+Pi= 6CO2+H2O+energy (atp and heat)
What is the delta G for the breakdown of glucose?
- 2870kJ/mol
How is the energy of glucose released
Redox reactions.the reaction for aerobic cellular respiration consists of many intermediate steps where almost every step is catalyze by a distinct enzyme. Our body temperature is not high enough
fo it to occur in one step-additionally, if energy is
Released all at once, it cannot beused efficiently for
Constructive work.
T or F: wo work in the cell is powered by phosphorylation
False. ATP powers much of the cellular work through phosphorylation, but a lot of work is powered by the simple transfers of electrons.
True or false: elections released duringthe oxidation process cannot exist in a free state in living cells. Every oxidation reaction must therefore be
Accompanied by a reduction reaction
True
What is oxidation and reduction
Oxidation: the loss of electrons by aless electronegative molecule , releases energy
Reduction:the gain of electrons by more electronegative molecule, receives energy
Watch a video on redox reactions
https://youtu.be/lQ6FBA1HM3s?si=oHCJVTOqY3qwjxpS
What are the electron carrier molecules? they, during key steps, receive electrons removed by glucose all while they are paired with a proton
Nad+(nicotinamide adenine dinucleoticle)
Fad (flavin adenine dinucleotice)
What do we know about NAD+ (NADH)
- most versatile electron acceptor in cellular respiration and functions in several redox steps in the breakdown of sugar
- it is a coenzyme to enzymes called dehydrogenases
- nad can cycle easily between oxidized NAD and reduced NADH states. As an electron acceptor, nad functions as an oxidizing agent and as NADH it temporarily stores a large amount of free energy
What does dehydrogenases (electron carrier) do?
- Removes a pair of hydrogen atoms (2e- and 2p+) from the substrate (glucose) thereby oxidizing it. - the enzyme delivers the 2 electrons with one proton to its coenzyme, nad+, the other proton is released as a hydrogen ion (H+) into the surroundings.
How does NADH work as an electron shuttle
When NADH transfersthe electrons to some other
Molecule, some of their energy is also transferred.
This energy is usually transferred through a series
Of reactions that ultimately lead to the synthesis of ATP (in cellular respiration)
Why do we use an electron transport chain for cellular respiration?
When H2 and 02 are mixed, they react explosively. This is due to a release of energy as the elections of hydrogen are pulled to the electronegative oxygen. If NADH released its electrons directly to oxygen.,the cell would not be able to harness this explosive energy to perform work. Instead, respiration uses an electron transport chain to break the fall of electrons to oxygen into several energy-releasing steps.
What do we know about electron transport chains?
- consists mainly of protein, built into the inner membrane of the mitochondria of eukaryotic cells and the plasma membrane of respiring prokaryotes
- electrons removed from glucose are shuttled by NADH to the tops higher-energy end of the chain.at the “bottom”, lower-energy end, 02 captures these electrons along with hydrogen nuclei (Ht) , forming water.
- every election transfer releases some energy which can then be harnessedto make ATP, the electrons energy level decreases with each transfer.
- each “downhill” carrier protein is more electronegative than, and thus capable of oxidizing its “uphill” with neighbour, oxygen at the bottom of the chain. Therefore, the electrons transferred from glucose to nad+ → NADH fall down an energy gradient in the etc to a far more stable location in the electronegative O2 atom
- the chain consists of many molecules, mostly proteins, which are built into the inner membrane of mitochondria.
What du we know about mitochondria
The mitochondria has a double membrane structure allows for this organelle to maintain two different environments.
Inner membrane space (between the inner and outer membranes)
Matrix enclosed by the inner membrane, contains many different enzymes as well as the mitochondrial DNA and ribosomes )
- The membrane separating these two environments is used during cellular respiration.
Where in the cell is the site of electron transport chain and chemiosmosis, the processes that together constitute oxidative phosphorylation (synthesizing ATP molecules)
The inner membrane of the mitochondrion
What is oxidative phosphorylation
Oxidation of NADH, and FADH2,by the etc provides energy ( hydrogen ion gradient) to decrease the activation energy (EA) needed for ATP synthase to make ATP. molecules of glucose degraded to CO2 and H20 by respiration, the cell makes up to about 32 molecules of ATP each with 30.5 kj/mol of free energy.
What is substrate-level phosphorylation
This mode of ATP synthesis occurs when an enzyme transfers a phosphate group from a substrate molecule to ADP, rather than adding an inorganic phosphate to ADP as in oxidative phosphorylation
What are the stages of aerobic cellular respiration?
- Glycolysis
- Pyruvate oxidation
- Citric acid cycle (krebs cycle)
- oxidative phosphorylation (etc)
What is glycolysis?
- The splitting of sugar
- occurs in the cytoplasm
- the first of two catabolic pathways that breakdown glucose and other organic fuels for energy.
In terms of glycolysis, what happens when O2 is present, what if 02 is not present?
- if O2 is present the chemical energy is stared in the end products of glycolysis ( pyruvate and NADH ) can be extracted within the mitochondria through aerobic cellular respirationthis method produces a lot more ATP.
-If O2 is absent, then pyruvate and NADH will be used in the cytoplasm for fermentation) yielding fewer ATP.
What are the two phases of glycolysis
- Energy investment phase
- I molecule of glucose used
- 2 molecules of ATP used - Energy payoff phase
- four molecules of ATP formed by substrate level phosphorylation
-2 molecules of NADH formed
- 2 molecules of pyrovate formed
What do we know about the energy-investment phase
- Glucose is converted from a 6-carbon sugar into two 3-carbon sugars, called glyceraldehyde-3-phosphate (G3P)
- the energy from the phosphorylation by 2 ATP molecules is required
- hexokinase and phosphor fructokinase (pfk) are important regulatory enzymes for the whole process of glycolysis. Their activation and inhibition is very tightly controlled. (More amp activate pfk , more citrate and more ATP inhibits PFK )
- phosphorylation of glucose occurs as soon as it enters the cell converting it into a different molecule.
- this maintains the glucose concentration gradient
- this also drives glycolysis in one direction, ensuring glycolysis proceeds towards.
- Glucose uptake most often occurs via facilitated diffusion through glucose carriers such as glut4.
What are the two steps in glycolysis in which ATP is consumed energy is invested)
- Glucose is converted to glucose-6- phosphate ( G6P.) by hexokinase
- Fructose-6-phosphate (F6P) is converted into fructose- 1,6 _biphosphate (F1-6BP) by phosphofructokinase (PFK)
Glycevaldehyde -3- phosphate (G3P) is the last molecule prior to the energy-payoff phase
Look over slides 33 - 34 of lecture 10a
Ok
Watch a video an glycolysis
https://youtu.be/SUPQVg1vO0Q?si=RgTM9ZJwuqaqmv66
What du we know about the energy payoff phase
- 2 molecules of G3P are oxidized and rearranged to form 2 molecules of private
-2 molecules of nad+ are reduced to NADH
-4 ATP are produced (2 per G3P) via substrate_ level phosphorylation
What are the two steps in glycolysis in which ATP is generated energy is gained
7.1,3 - bisphosphoglycerate is converted to 3- phosphoglycerate by phosphoglycerokinase
10. Phosphoenolpyruvate (pep) is converted into pyruvate by pyruvate kinase (pk)
The conversion of G3P into 1,3 -biphosphoglycerate yields energy in the form of NADH
- note that the number of each molecule in this phase is doubled.
What is phosphofructokinase (PFK) regulation
- PFK is allosterically inhibited by ATP or citrate (from the citric acid cycle) when their concentrations are elevated
When the activity of PFK is inhibited it stops the process of cellular respiration - when the levels of ATP and citrate drop and the levels of amp are elevated, amp allusterically activates PIK inte action and cellular respiration starts up again
True or false most organisms cannot live by glycolysis alone and rely on the stages of cellular respiration that follow glycosides to satisfy their energy reeds
False. Only yeast and certain bacteria can make do with the energy provided by glycolysis alone
Look over slide 43 of lecture 10a
yas
What do we know about the pyruvate stage of cellular respiration
- each pyruvate formed in glycolysis must enter a mitochondrion ( must pass through both the outer and inner membranes of a mitochandrich into the matrix where the citric acid cycle occurs)
- passage through the outer membrane is by facilitated by diffusion
- passage through the inner membrane into the matrix is via a pyrovate /h symport carrier protein
- there will be no H gradient if there is no 02. This means pyruvate cannot cross into the matrix (remains in intermembrane space)
what are the stages of pyruvate oxidation
- The carboxyl group of pyruvate is removed and is given off as CO2 which then diffuses out the cell into the blood for transport to the lungs
- The remaining fragment is oxidized into acetate. An enzyme (pyruvate dehydrogenase) transfers the 2 e- and a hydrogen from this oxidation to NAD+, storing energy as NADH
- Coenzyme A is attched to acetate by an unstable bond, making the molecule very reactive. Acetyl CoA can now enter the citric acid cycle.
YIELDS 2 CO2 MOLECULES PER GLUCOSE MOLECULE, YIELDS 2NADH MOLECULES PER GLUCOSE MOLECULE. THIS ID THE FIRST STEP WHERE CO2 IS GENERATED IN CELLULAR RESPIRATION.
T or F all Acetyl CoA moves on the citric acid cycle (aka krebs cycle)
F, some will enter different metabolic pathways, for example, used to make fatty acids and cholesterol
what are the goals of the citric acid cycle
- complete the breakdown of glucose
-store electron energy via oxidation (NADH+ FADH2) - create ATP by substrate-level phosphorylation
what is the enzyme invovled in step 1 of the citric acid cycle
citrate synthase
what are the products of the citric acid cycle
2ATP PER GLUCOSE
6 NADH PER GLUCOSE
2 FADH2 PER GLUCOSE
4 CO2 PER GLUCOSE
watch a video on te citric acid cycle
https://youtu.be/juM2ROSLWfw?si=JECi54mPuc9W6kte
how many ATP molecules is obtained using glycolysis and the krebs cycle
4
what accounts for most of the energy extracted from food
NADH and FADH2 account for most of the energy extracted from food
what links FADH2 link glycolysis and the citric acid cycle to oxidative phosphorylation
NADH and FADH2
What are the two processes in oxidative phosphorylation
- Electron transport chain
- oxidizes NADH and FADH
- Creates H+ gradient across the inner mitochondrial membrane. - Chemiosmosis
-Phosphorylation of ADP by ATP synthase enzyme
- Energy provided by the H+ ion gradient
watch this video on cellular respiration
https://youtu.be/eJ9Zjc-jdys?si=OVtLe-ogTj7X58sj
what composes most components of ETC?
proteins containing prosthetic groups, non-proteins components essential for the catalytic function of certain enzymes.
how are the components of the ETC ordered
increasing electronegativity
electron transfer is….
exergonic
do electron carriers alternate between reduced and oxidized states as they accept and then donate electrons?
YA
- Each component becomes reduced when it accepts electrons from its “uphill” neighbour, which has a lower affinity for electrons
- it becomes oxidized as it passes electrons to its “downhill’ more electronegative neighbour
what is the first electron acceptor in ETC complex 1? what is it followed by?
flavoprotein, followed by a series of proteins called iron-sulfur clusters
how many protons are pumped across the inner mitochondrial membrane through ETC complex 1
4H+
What is the last electron acceptor of complex 1?
Ubiquinone (aka coenzyme Q, CoQ), which is not stuck in place like the other molecules. It travels inside the membrane to the next complex- COMPLEX 3
when does the FADH2 created during glycolysis enter the ETC
complex 2
what are the electrons formed from FADH2 accepted by? What is it then used for?
Fe-S centers, and then used to reduce a heme (iron) molecule before reaching ubiquinone (CoQ).
where does the CoQ travel to?
it travels through the inner mitochondrial membrane and reach complex 3
define cytochromes
the remaining electron carriers between ubiquinone and O2 proteins: they are proteins with a heme moiety as their prosthetic group.
what causes the differences in cytochromes?
The different nature of each cytochrome’s prosthetic group results in its variable electronegativity
what is the last cytochrome of the ETC chain ?
Cyt a3
what does Cyt a3 do?
passes its electrons to O2, which is the most electronegative electron acceptor in the chain. Each oxygen atom also picks up a pair of H+ (protons_ from the aqueous solution, forming water
what do complexes 3 and 4 of the ETC do?
3: pumps 4 H+
4: pumps 2H+
recall the oxidation of NADH
- energy is released is used to pumps prtons (H+) from matrix to inter-membrane spaces
- complex 1, 3, and 4 are pumps, 2 is NOT
- electrons from 1 NADH release enough energy to pump 10H+ across
recall the oxidation of FADH+
- electrons from FADH2 release enough energy to pump 6H+ across
why is o2 important in the ETC
- the fianl electron acceptor in the ETC
- without o2, h+ ions could not be pumped across the membrane since ETC would be blocked due to a lack of a final and renewable electron acceptor at the end of the chain
- oxygen contributes to the h+ gradient created by the ETC by taking H+ ions out of the mitochondrial matric to form H2O
how many protons are transport across the inner mitochondrial membrane during one ETC run per complex. How many NADH are transported? what about FADH2?
1: 4
2: 0
3: 4
4: 2
NADH: 10
FADH: 6
how do poisons usually work
they inhibit the processes of the ETC
how is cyanide poisonous
it binds to cyt a3 in complex 4 which prevents the release of electrons to oxygen which stops all of the ETC. WIthout a proton gradient, chemiosmosis cannot occur and the cell is depleted of ATP and dies
what do we know about chemiosmosis
- process in which and ion concentration gradient across a membrane is used to drive cellular work (like synthesizing ATP)
-the processcouples the etc to the creation of ATP - requires the action of an embedded enzyme called ATP synthase
- ATP synthase uses of energy an existing ht gradient across the inner mitochondrial membrane to power ATP synthesis
Can ATP synthase work in both directions?
Yes. Depending on the change of free energy of the reaction, it a can hydrolyze ATP or synthesize it
What do we know about atp-synthase,?
- A multi- subunit complex with 4 main parts, each made up of multiple polypeptides:
Here are the submits:
1. A rotor within the membrane spins when H flow past down the hydrogen gradient
2-a stator anchored in the membrane holds the knob stationary
3. A rod(or “stalk”) extending into the knob also activating spins, catalytic sites in the knob
4. 3 catalytic sites in the stationary kerob join phosphor ae in organic to ADP to make ATP
How does ATP synthase work?
- Protons move one by one into the binding sites on the rotor, causing it to spin in a way that catalyze ATP production from ADP and inorganic phosphate.
- the flow of protons behaves like a rushing stream that turns a waterwheel.
- ATP synthase is the smallest molecular rotary motor known in nature
What do we know about ATP synthase’s stationary knob?
- has 3 active sites that catalyze the phosphorylation of ADP into ATP
- the rod and rotor spin in response to the flow of hydrogen down the center
- the rotation causes conformational changes in the stationary knob activating the 3 catalytic sites in the knob sequentially and continually such that ADP and Pi combine to make ATP.
How much ATP do NADH and FADM2 give?
1 NADH = 3 ATP
1 FADH2 =2 ATP
What is the theoretical maximum number of ATP produced per glucose molecule?
38
The or false: ATP produced per glucose varies
True!
Which organisms make ATP without 02?
Obligate and facultative anaerobes
What is the difference between obligate and facultative anaerobes?
Obligate: organisms that can only live in anaerobic conditions ( oxygen is toxic to them)
- obtain ATP via glycolysis and the regeneration of nadh+ through fermentation or anaerobic respiration
Facultative: organisms or cells much live in both anaerobic and aerobic conditions
- aerobic cellular respiration if O2 is present, fermentation if there is no 02
What is the determining factor of what type of respiration will take place?
Presence of oxygen. Glycolysis occurs whether there is oxygen or not, it is the proceeding steps that are affected
Why is less ATP created during anaerobic cellular respiration?
The final electron acceptors are not as electro negative as oxygen.
What are the steps of anaerobic respiration?
- Sugars (carbs) are oxidized during glycolysis, producing nada. This NADH carries electrons to the election transport chain in the mitochondria
2.in the etc, NADH and FADH2 molecules are oxidized thereby donating their electrons to the various electron carries of the etc
- electron acceptor is nitrate, nitrite, CO2 ) metal ions, sulfate, etc. - ATP is made by ATP synthase through chemiosmusis using a hydrogen gradient
For false fermentation does not use oxygen or any etc
True
What happens during fermentation
Pyruvate is incompletely broken down, but NADH is recycled by substrate-level phosphorylation so that glycolysis can be sustained
What are the two types of fermentation?
- alcohol
2.lactic acid
What are the steps of alcohol fermentation?
l. Glycolysis
2. Pyruvate is converted to ethanol in two steps:
- carbon dioxide is released from pyruvate, making acetaldehyde
- acetaldehyde is reduced by NADH to ethanol, resulting in nad +
What are the steps of lactic acid fermentation?
- Glycolysis
- Private is directly converted to lactate, regenerating nad+- there is no release of cO2
This happens in our muscles
How does lacticacia build up in our muscles?
- Human muscle cells make ATP by lacticacid fermentation when oxygen is scarce:
Glucose catabolisms is greater than the rate of oxygen intake, which results in lactic acid
How does the body rids itself of lactic acid buildup?
Most lactate is transported via the blood to the liver where it is converted back Tc glucose or pyruvate
- BC oxygen is available in the liver, this pyruvate can then enter the mitochondria in liver cells and complete cellular respiration
What is the breakdown of glycogen to glucose called?
Glycogenolysis(results in glucose 6-phosphate)
Where in the body are the glycogen “ storage units”
The liver and the muscle
True or false the liver and the muscle are organs that both supply other organs with glucose obtained through glycogenolysis
False. First off, muscle is a tissue
The liver is the only part of the body that supplies other organs with glucose obtained through glycogenolysis
Muscles break down their glycogen reserves for their own energy needs
- when need exceeds supply, glucose is provided by the liver glucose distribution
Recall: excessive ingestion of carbs increases body fat) which increases insulin levels in blood which then promotes the absorption of carbs in liver and fat cells
- excess carbs are converted into glycogen (liver/muscle cells) for intermediate-term energy storage
They are converted to fatty acids (liver/adipose cells ) and incorporated into fats for long -term energy storage
yas
How are proteins used for ATP?
- It is broken down into its constituent amino acids - many of these amino acids are used to make other proteins, but excess amino acids (not used fer protein synthesis) can be converted (with enzymes) to intermediates of cellular respiration
What is amino acid deamination?
Amino acids most have their amino groups removed prior to entering cellular respiration via deamination
-Removed amino groups result in ammonia, which is toxic to humans. The Body converts it into ammonium and then urea which is then excreted
How are lipids used in ATP?
After fats are digested to glycerol and fatty acids, ( lipolysis), the glycerol is converted to glyceraldehyde-3 - phosphate (G3P) , an intermediate of glycolysis (the last intermediate of the energy investment phase of glycolysis). Most of the energy of a fat is stored in the fatty acids
How are fatty acids broken down for ATP?
- broken down through beta oxidation. This yields fragments that are 2-carbon in length and enter the citric acid cycle as acetyl-coa
- 1 gram of eat yields more them twice the amount of ATP as 1 gram of carbs!
True or false NADH and FADH2 are not generated during beta oxidation
False they are generated and then enter tu etc, leading to further ATP production.
When body cells perform beta-oxidations) where do they go?
Fatty acids taken up by cells are transported into the mitochondrial matrix for the process.
Look over the palmate area example from lecture 11
Ok.
Ultimately, where do we get energy
From the sun!
What is the difference between autotrophs and heterotrophs?
Auto: self-feeders, producers
Hetero: “other” _feeders, consumers
Define photo autotrophs
Organisms that use light as a source of energy to synthesize organic substances.
- Sunlight to sugar via photosynthesis
- they use carbon dioxide as their source of carbon
Recall photosynthesis uses light energy to drive a redox reaction resulting in the production of sugar.
Ok
What is the difference between oxygenic photosynthesis and anoxygenic photosynthesis
Oxygenic: uses water, produces oxygen
Anoxygenic: uses hydrogen sulfide ) , produces sulfur
Plants produce their own glucose through photosynthesis what leaf and plant structures aid in photosynthesis?
Mesophyll, stomata, vascular tissue, chloroplasts
What does leaf tissue consist of?
Epidermis, vascular tissue, mesophyll
- chloroplasts and stoma are smaller-components within the mesophyll and epidermis, respectively
What do we know about the epidermis
- Coated with a waxy cuticle to avoid desiccation) prevents water from escaping and keeps eon and 02 from passing through
- contains stoma that allow for gas exchange in the lower epidermis
What do we know about vascular tissue
- System of vessels that distribute substances throughout a plant
- critical to the survival of all plant cells.
What do we know about the mesophyll
- Composed of cells that perform photosynthesis in leaves
- contain an extremely high amount of chloroplasts for photosynthesis
Do all plant cells in any plant have chloroplasts? Can they au intergo photosynthesis?
Yes, to some extent
What do we know about chloroplasts?
- Sites of photosynthesis
- contain the green pigment chlorophyll, along with enzymes and other molecules that function in the photosynthetic production of sugar
- have a double membrane, like mitochondria
What is part of the double membrane in chloroplasts?
Fluid within the inner membrane (stroma) that contains DNA and enzymes.
The stroma also contains internal structures called thylakoids, which are stacked and form towers each called a geranium
Are chloroplasts static?
Their shape is changeable they grow, and even pinch in two
They are also mobile and move around the cell along the cell tracks of the cytoskeleton
How can chloroplasts convert light energy into chemical energy
They contain pigmentsthey absorb light
What pigments do we find in a plant cell?
- chlorophyll a
- chlorophyll b
-Carotenoids
What do we know about chlorophyll a, b and carotenoids
Chlorophyll a and b
- chlorophyll a is the key light-capturing pigment
- chlorophyll b works in conjunction with chlorophyll -they differ in one functional group (CH3 in a and Cho in b) both have a central atom of magnesium
Hydrophobic tail stabilize the pigment in the thylakoid membrane
Carotenoids
-Yellow-orange coloration
-Chlorophyll breaks down in response to colder temperatures
- have the job of photoprotection
- absorb and dissipate excess light to prevent damage to the chlorophyll pigments
- prevent the formation of free radicals
What is the visible light range that is used for photosynthesis
380 nm - 750 nm
What light is absorbed by chlorophyll a and b.
Violet-blue and red
A absorbs blue-green
B absorbs yellow-green
What is the only colour reflected by chloroplasts?
Green.
What colour light is absorbed by carotenoids
Violet and blue-green
Since chlorophyll molecules are not isolated, absorbed energy is not released as heat vibration, nor light. What happens?
Light energy is absorbed by Che pigment molecule can be transferred to another
- electrons are excited in series until they reach a reaction center: inductive resonance
- vibration energy is transferred from one pigment to the next until it reaches a reaction center.
Recall: only photons whose energy is exactly equal to the energy difference between the ground and excited states of a pigment molecule.this explains the specificity of certain pigment molecules fer certain wavelengths.
Ok
Define a photosystem
Reaction-center complex surrounded by several light-harvesting complexes. A reaction- center complex is an organized association of proteins holding a special pair of chlorophyll a molecules
Where can we find light-capturing pigments
In two photosystems in phylakoid membranes of chloroplasts
For false, some of the glucose produced by plants is used to make ATP in cellular respiration
True
Where does most of the glucose made via photosynthesis used for?
- Used to synthesize macromolecules leg starch and cellulose), which will be incorporated into the tissues of the plant. This is called carbon fixation
Photosynthesis is a redox reaction, what is reduced? What is oxidized?
CO2 gets reduced,
- all of the c atoms it holds are fixed into sugar
- half of the o atoms go into making sugars and the other half into making water
water is oxidized
-Oxygen atoms are released as 02
- hydrogen atoms are transferred to form sugars.
Photosynthesis occurs in two steps. Summarize them.
- Light reactions
-Occurs in thylakoid membranes
- takes in light energy and water panel generates 02, ATP, and nadph - Calvin cycle
- light-independent reactions
-Occurs sin the chloroplast stroma
- takes ATP, nadph, and CO2 and generates sugar molecules
What do we know about light reactions?
- membranes light can pass through: the plasma ‘ membrane, the chloroplast membrane, the thylakoid membrane
-The light reactions of photosynthesis occur in the thylakoids(light energy= ATP and nadph)
What is the het equation of light reactions
Light + H2O+ NADP + ADP +pi = 02 + ATP + nadph
Which structures in the chloroplast thylakoids are involved in the light - dependent reactions
Photosystem II and I (psi and psi)
Electron transport chain 1 and 2
ATP synthase and nadp+ reductase
Photosystems are made up of two components ) what are they?
- Light harvesting complexes
- contains pigment molecules which surround the reaction center complex
- Electrons transfer energy gained by photon through
Inductive resonance to a neighbouring pigment. - Reaction center complex
- have a specialized pair of chlorophyll a pigments that transfer an excited election to the primary electron accepter
Remember:the election transfer only occurs in the reaction center between chlorophyll a molecules and a primary electron acceptor
Ok.
What is a reaction center?
- Protein complex that contains a special pair of chlorophyll a molecules and a primary electron accepter the special pair of chlorophyll molecules uses the energy from light to boost one of their electros to a higher energy level and to transfer it to a different molecule: the primary electron acceptor
True or false psi functions before ps II
False. PS II functions first
What is the difference between psi and PS ii?
They differ in their reaction centers. Each has a specific type of primary electron acceptor next to a special pair of chlorophyll a molecules associated with specific proteins
- PS2 has reaction center P680 (optimal light absorbency from chlorophyll pair at 680 nm )
- PSI has reaction center P700(optimal light absorbency from chlorophyll pair at 700 nm)
The difference is caused by the p roteins associated with the chlorophyll moleculesthe chlorophyll molecules themselves are identical
What happens when a P680 primary electron is left with an oxidized pair of chlorophyll a molecules?
- Water is split by an enzyme to replace the electrons taken from the chlorophyll a molecules in the photosystem 2 reaction center
- oxygen is generated as a product
- hydrogen proton, are released into the thylakoid space
- electrons are taken by chlorophyll a one at a time, there were remaining in the rx center
What happens when excited electron from P700 is transferred to the primary accepter of psi and then transferred to ETC2
Ferredoxin accepts the electrons from the primary acceptor and transfers them to nadp+, generating nadph
- catalyze by the enzyme nadph reductase
- No hydrogen gradient is made sono ATP is made
The electrons from etc are transferred to P700 to regenerate their initial reduced state.
What is the etc 1 chain made up of (photosynthesis)
- plastoquinone ( pq)
-Series of cytochromes (cyt)(gradient) - plastocyanin (PC)
- P700 in psi
What does etc 1 do? (Photosynthesis)
Etc 1 creates a proton gradient in the thylakoid membrane which drives chemiosmosis and synthesizes ATP
What is the nadph electron carrier
Nadp+: nicotinamide adenine dinucleotide phosphate
What is the difference between coenzyme nadp+ and nad+
The main difference with nad+ is the presence of an extra phosphate group
There are two possible roads for the electron for through the photosystems , what are they?
- Linear electron flow
-PS2 , etci,psi,etc2
-Makes ATP and nadph
-Makes 02 - Cyclic electron flow
- only go through psi and uses etc1 instead of etc 2
- makes ATP only
-No oxygen made
What do we know about linear and cyclic electron flow?
Refer to slicks 17 and 18 in lecture 12b
What is the purpose of cyclic electron flow?
- A temporary shift from linear to cyclic e-flow can occuruntil supply of ATP is nigh enough again. This is because of now linear electron flow produces as much ATP as it does nadph, but the Calvin cycle (dark rx) consumes more ATP than nadph. If the Calvin cycle runs low on ATP, nadph Will accumulate as the Calvin cycle slows down
Define photophosphorylation
The conversion of energy from a light- excited electron into the phosphate bond of an ATP molecule
What are the steps of photophosphorylation
1 light energy boosts the energy state of an electron. Then the electron is transferred to a primary electron acceptor in a photosystem
- the electron is then transferred to an etc
2. Transport through the etc lowers the energy level of electrons. This released energy is used to create a il gradient across the thylakoid membrane
3. Chemiosmosis by ATP synthase: the proton gradient drives ATP synthesis
How is etc involved in photophosphorylation
Etc I pumps pretens across the thylakoid membrane from the stroma into the thylakoid space, against its concentration gradient protons then accumulate in the thylakoid space.
Where is ATP synthesized in plants?
In the stroma, making it available for the Calvin cycle.
Compare ATP synthesis in the mitochondria and in the chloroplast
Slide 23 lecture 12b
What do we call the reactions when c enters the Calvin cycle in the term of CO2 and leave in sugars?
Dark rx, light-independent pathways
Watch a video on the Calvin cycle
Ok.
What is he sugar produced by the Calvin cycle?
glyceraldehyde-3- phosphate (GBP) not glucose itself
How many terms of the Calvin cycle produce G3P?
3
What are the 3 phases of the Calvin cycle?
- Carbon fixation
2- reduction
3 regeneration of the CO2 acceptor
Refer to slides 26 -34
What is one of the major problems facing terrestrial plants?
Dehydration
What is problematic when it comes to stomata, photosynthesis, and dehydration?
Stomata close to conserve water, reducing the ability for the plant to obtain carbon dioxide for the Calvin cycle
What are C3 plants?
Plants that use rubisco in the carbon fixation stage - the first organic product of fixation is a 3-carbon compound (3-pga)
- 85% of plants are C3 plants
What are the different types of C3 plants?
Mesophytes- live in temperate climates
Hydrophytes (water plants)
How do C3 plants conserve water?
C3 plants open in the day and close at night by actively pumping ions in and out of guard cells.
-Water flows to the hypertonic side of the membrane
En C3 plants, what is a means to conserve the Calvin cycle
Photorespiration
Photo respiration occurs in C3 plants when they are in not, dry, conditions and their stomata partially or fully close. what is the result?’why is it not effective?
Carbon dioxide levels decrease, oxygen levels increase inside the chloroplasts
Photorespiration is a wasteful pathway for plants because it consumes ATP and does not produce sugar
Why do plants undergo photorespiration if it isn’t effective?
’ Oxygen is a direct competitor for rubisco’s binding site. When carbon dioxide levels decrease and oxygen levels increase, rubisco starts to interact with oxygen.
- instead of creating a molecules of 3-pga, one 3-pga and 2 A carbon molecule is formed
- the two carbon molecule can later be split into two moleute5 of carbon droxiche by peroxisches and mitochondria in the plant cell.this only happens if the cone. Are high enough to outcompete oxygen.
What ave the possible effects of photo respiration that is positive
- Plants with genetic detects can’t switch to photo respiration often suffer damage from excess light
What are C4 plants
Adaptations have evolved in C4 plants and CAM plants living in hot and arid climates to minimize/prevent photorespiration leg corn and succulents) ‘
Both C4 and cam plants use the following pathways, albeit in slightly different ways
1.C4 pathway makes the 4-carbon molecule oxaloacetate
2.C3 pathway: the same procedure as in C3 plants
-Makes (3 - PGA)
What do we know about c4 plants?
- The two path ways used for carbon fixation ( C4 and C3 pathways) are separated by location
c4 occurs in mesophyll cells, C3 pathway occurs in the bundle sheath cells. Mesophyll cells are arranged differently in C4 plants - while in all plants mesophyll cells contain cheroplasts, in C4 plants only, bindte sheath cells also have culcroplasts.
What do we know about c4 plants?
- The two path ways used for carbon fixation ( C4 and C3 pathways) are separated by location
c4 occurs in mesophyll cells, C3 pathway occurs in the bundle sheath cells. Mesophyll cells are arranged differently in C4 plants - while in all plants mesophyll cells contain chloroplasts, in C4 plants only, bindte sheath cells also have chloroplasts.
What is the carbon fixation pathway in c4 plants?
1 - carbon dioxicle is added to phosphoenolpyruvate (pep) (3C) form to oxaloacetate (4C)
Enzyme-pep carboxylase (fixes carbon dioxide)
Location: mesophyll cell
Pep carboxylate has a higher affinity for coz than does rubisco and has no affinity fer oxygen
-The product diffuses into sheath cell
-Regenerative, CO2 goes into the mesophyll and allows it to undergo the Calvin cycle and not photo respiration
Compare C3 and C4 plants
C3 (mesophyll cells house the Calvin cycle, loss of up to 58% of all curban fixed by the Calvin cycle during photo respiration
What are cam plants
Cam=crassulacean acid metabolism
-Present many pineapples, cacti, etc.
- stomata are open at night ( allows carbon dioxide to enter where it can be stored for use during the day)
Anatomy of leaf: xerophytes (C3)
In cam plants, the 2 pathways used fer carbon fixation CCD land (3 pathways) are separated temporally
_ C4 at night in mesophyll, C3 during the day in mesophyll
Compare C4 plants and CAM plants
Lecture 13 table
