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Hydrophobic, non-polar molecules cross membranes with ease.
Hydrophilic molecules cannot slip through hydrophobic core of membrane: Require help of proteins that span the entire membrane.
What kinds of molecules may pass through the lipid portion of a cell membrane unaided?
Which portions of a membrane-spanning protein that allows passage of polar or charged ions/molecules are hydrophilic, which are hydrophobic?
Amino acid R (rest) groups
-Nonpolar R groups: hydrophobic
-Polar (OH bonds, DOuble bonds, Nitrogen pulls) R groups, Electrically charged R groups: hydrophilic
(see molecules in slide)
Membrane-spanning protein channels allowing (polar) water to move across (hydrophobic) lipid membranes
When a protein is needed for movement:
When ATP energy is needed for movement:
How does glucose move from the gut into intestinal cells when the glucose concentration in the gut is higher than in the intestinal cells after a meal?
•Cholesterol is transported in the bloodstream via LDL (low density lipoprotein).
•Cholesterol is removed from arteries when the LDL protein binds to a receptor in the membrane and is removed from the bloodstream
via receptor-mediated endocytosis.
To move whole proteins, e.g. LDL, across membranes, membrane vesicles are utilized (requires energy)
Genetic predisposition for high cholesterol levels in the bloodstream=
caused by inefficient version of the receptor for removal of cholesterol (LDL) from blood stream
Cholesterol and Cardiovascular Disease
Part genetic problem (LDL receptor gene)
AND part dietary problem
Dietary saturated fats and trans fats downregulate gene expression of the LDL receptor gene: So, less LDL receptor protein is available in cell membrane to remove LDL from blood!!
1. Water-soluble protein hormones relay message via signal transduction pathway to a gene regulatory protein.
2. Lipid-soluble (e.g. steroid) hormones move into nucleus & bind directly to gene regulatory protein.
Which hormones can pass directly through the lipid bilayer of membranes?
Which hormones enter a target cell without the aid of a membrane-spanning transport protein, and thus activate gene regulatory proteins directly?
Which component of animal membranes acts as a temperature buffer, both increasing fluidity at low temperature and decreasing fluidity at high temperature?
In warm climates, plants have relatively more ______________ than ________________ fatty acids compared to plants from cold climates.
Energy for all cellular work is provided by the same energy-rich compound....
ATP (adenosine tri(3)phosphate)
A cell constantly performs work that requires energy to stay alive
ATP consists of three phosphate groups:
ATP links the energy from breakdown of energy-rich food molecules to cellular work
1. High-energy P transferred to motor proteins for mechanical work
ATP transfers phosphate group to motor protein (phosphorylated motor protein = energized)
2. High-energy P transferred to transport proteins for transport work
Membrane protein (Na+/K+ pump)
3. High-energy P transferred to reactant molecules for chemical work
-(ATP adds phosphate group to glutamic acid, making it less stable.)
-(Ammonia displaces phosphate group, forming the amino acid glutamine.)
forming the amino acid
A) ATP serves as a main energy carrier inside cells.
B) In the cell, ATP drives reactions that require energy by the transfer of a phosphate group to specific reactants.
C) The regeneration of ATP from ADP and phosphate is a reaction that requires energy.
Why is ATP is not used to store energy (but is instead used to produce sugars in photosynthesis)?
• ATP is too unstable to serve as an actual
storage form of energy.
• Therefore, C-H bonds in macromolecules (e.g. sugars) are instead used for energy storage.
*Sugar; stable, but not usable for cellular work
*“Small change”; usable, but unstable (=reactive)
Sugars are made with solar energy in photosynthesis, and cellular respiration converts the energy of sugars back to ATP as needed.
CO2 + H2O <----> [CH2O] + O2
Fueled by sun's energy
6 CO2 + 6 H2O <-----> C6H12O6 + 6 O2
Providing ATP released in respiration
Plant photosynthesis occurs in...
• Inner membranes (thylakoids):
Light reactions (light collection by chlorophyll & electron transport)
• Fluid space (stroma): Conversion of CO2 to sugars in Calvin cycle
-Solar energy drives production of energy-rich ATP & NADPH
-ATP & NADPH drive conversion of CO2 to energy-rich sugar
Light collection – solar energy used to strip electrons from water, energize electrons, make ATP & load energized electrons onto NADPH
What is the ultimate source of the electrons used to produce NADPH and then used to produce high-energy C-H bonds in sugars from CO2?
The electron acceptor at the end of the electron transport chain in chloroplasts is ________.
In the model of the hydroelectric dam, water stands for ________, the turbine stands for ________, and the lit-up light bulb stands for _________.
the protons (H+), the ATP synthase, the ATP produced
B) the proton gradient across the thylakoid membrane
C) the H (electrons and H+) loaded onto NADPH
D) the ATP formed
*Most plants (C3 plants) use only Calvin cycle: First product has 3 carbons (phosphoglycerate).
*Some plants (C4 plants) use additional CO2 fixation cycle before Calvin cycle: First product has 4 carbons
Advantages of C4 Plants:
-PEP carboxylase fixes CO2 better than RuBP carboxylase:
C4 plants can fix CO2 with stomates less widely open & need less water & less nitrogen fertilize
-Advantage in hot, dry, sunny climates & under nutrient limitation
Advantage of C3 plants:
-C3 plants need less energy since they don’t run two cycles
-Advantage in less sunny, moist, cool climates. Typically more cold-tolerant.
What are produced by light collecting and electron transport reactions in photosynthesis and are utilized in the Calvin cycle?
Plants grown in the shade typically have _____ Calvin cycle enzyme levels compared to plants grown in the sun.
Predict the relative rates of photosynthesis versus respiration in a green leaf.
Overall photosynthesis rates should be higher, because you have to be able to store and feed the plant
1. food molecules to
2. electron carriers (NADH and FADH2, transferring electrons and H+)
3. the electron transport chain (leading to ATP synthesis)
* Same principle used for ATP formation in mitochondria & chloroplasts
Phase 1. Sugars are broken down in steps, starting with glycolysis in cytosol
Phase 2. Pyruvate is broken down to CO2 in citric acid cycle in mitochondria
citric acid cycle in mitochondria
Phase 3. Energy of C-H bonds is transferred to NADH & FADH2 and then
they feed electrons into electron transport chain to make ATP (most ATP is formed here)
Pumps protons against the concentration gradient; builds up a high H+ concentration in intermembrane space
Terminal electron acceptor of the mitochondrial electron transport chain
*Protons flow downhill through the ATP synthase, driving phosphorylation of ADP to ATP.
Cells use the energy of energy-rich food molecules to form ATP. Which of the following represents a state of high energy?
A) the C-H bonds in food molecules
B) the H (electrons and H+) loaded onto NADH
C) the proton gradient across the mitochondrial membrane
D) the ATP formed
E) all of the above
Every energy transformation leads to a loss of usable energy as heat (=unusable energy)
Humans generate much more heat than alligators. This is due to...
A) a greater number of energy transformations per minute in humans
B) a higher percentage of energy loss per transformation in humans
-Produce heat in newborns, small mammals in cold climates, & hibernating animals.
-Brown fat cells have many mitochondria
-and use uncoupling protein to uncouple electron transport from ATP formation to generate only heat
and no ATP
How does the mitochondrial uncoupling protein do this?
The mitochondrial uncoupling protein provides a channel across the membrane through which protons (H+) flow back downhill without making ATP, releasing all energy as heat
A) No proton gradient is produced.
B) No ATP is produced by the ATP synthase.
C) Glycolysis, citric acid cycle, and electron transport continue to run, and the energy is released as heat.
A diet pill that promises to burn fat without the need to exercise (and acts on mitochondrial respiration) is likely to
What would be the result of blocking electron transport
by cyanide or carbon monoxide? CN or CO vs. OO (O2)
The cellular respiration pathway breaks down & inter-converts... (3 components)
Which molecules can be utilized (directly or after some breakdown) in the cellular respiration pathway to generate ATP energy?
A) amino acids and proteins
B) glycerol and fatty acids
C) glucose and sucrose
D) starch and glycogen
E) all of the above
Cells release the energy of energy-rich food molecules. Which of the steps below represents a change from one form of energy to another?
A) use of energy-rich electrons to build up a proton gradient
B) use of the proton gradient to drive ATP formation
C) use of an uncoupling protein for thermogenesis
D) all of the above
Both mitochondria and chloroplasts produce...?
The electron acceptor at the end of the electron transport chain in mitochondria is ________ and in chloroplasts is ________.
The electron donor that directly feeds electrons into the electron transport chain (ETC) is ______ in mitochondria and ________ in chloroplasts.
What does NOT require a direct association with membranes?
A) adding electrons and H+ to, or removing them from, carbon-based molecules
B) ATP synthesis by ATP synthase
C) proton transport
D) electron transport
E) light absorption in chloroplasts
In both mitochondria and chloroplasts:
•Carbon conversion cycles in fluid space
•Electron transport chain & ATP synthase on inner membranes
While __________ are generated by mitochondria, ________ are generated by chloroplasts.
water and carbon dioxide; glucose and oxygen
•Only when oxygen is present can glucose be broken down completely in the mitochondria
for high energy yield
Predict whether a cell would be likely to run out of ADP...
How about NAD+? When O2 is absent, mitochondrial electron transport stops and NADH can no longer drop off electrons
Predict what happens in the absence of O2:
Glycolysis stops unless NADH is used for something else
Alcoholic fermentation (forms ethanol plus CO2) by yeasts and bacteria under anaerobic conditions (Yeasts use alcoholic fermentation to convert hexoses (from sugar cane sucrose or corn starch or cellulose) into ethanol for fuels)
Lactic acid fermentation
•Other fungi & bacteria
•Also in muscle cells under anaerobic conditions
Different human muscle fibers use different metabolism
*Fast-twitch glycolytic fibers (for sprint) use glycolysis - quick, but does not provide much energy.
*Slow-twitch oxidative fibers (with many mitochondria for extended exercise) use oxidative respiration -slower, but yields much more energy.
Which process in eukaryotic cells is NOT affected by whether oxygen (O2) is present or absent?
A) mitochondrial electron transport
B) photosynthetic electron transport
C) ATP production in mitochondria
*Because photosynthetic electron transport is dependent on water
A) In the absence of NAD+, glycolysis can still function.
B) NAD+ is converted to NADH during both glycolysis and the citric acid cycle.
C) NADH has more energy than NAD+.
D) NADH can transfer electrons into the mitochondrial electron transport chain.
Fermentation- partial degradation of sugars that occurs without the use of oxygen (Fermentation in absence of O2)
Anaerobic Respiration- oxygen is consumed as a reactant along with organic fuel (Aerobic respiration in presence of O2)
Which metabolic process is most closely associated with membranes?
Cellular respiration harvests the most chemical energy from which of the following?
the mitochondrial part of cellular respiration (citric acid cycle, electron transport, and ATP synthase)
Which does not take place in the cytosol?
A) alcohol fermentation
C) accumulation of K+
D) Calvin cycle
E) lactic acid fermentation
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