Cell Biology Exam 3

True or False: the inner membrane of chloroplasts is equivalent to the inner membrane of mitochondria in terms of energy transformation.

False, the inner mitochondrial membrane is equivalent to the thylakoid membrane of the chloroplast

What are the four distinct chloroplast compartments?

1. pair of envelope membranes

2. stroma

3. thylakoid membrane

4. lumen (interior space of thylakoid)

The ___ envelope membrane of the chloroplast is selectively permeable.

inner

The ___ of the chloroplast contains metabolic enzymes, chloroplast genome, and ribosomes.

stroma

What part of the chloroplast contains photosystems and ATP synthase?

thylakoid membrane

What part of the chloroplast is the location where water is split and oxygen is evolved during photosynthesis?

the lumen

Is the chloroplast genome larger or smaller than mitochondrial genomes?

larger

How many genes make up the chloroplast genome?

around 100-200 genes

What is the photosynthesis equation?

light + CO2 + H2O → sugar + O2 + heat

Where do the light dependent reactions of photosynthesis occur?

in the thylakoid membrane

Where do the light independent reactions of photosynthesis occur?

in the stroma

What is used to fuel light independent reactions of photosynthesis?

CO2 is used

What is used to fuel light dependent reactions of photosynthesis?

light energy is used

When water is split, producing oxygen, this is part of a light _____ reaction.

dependent

Light ______ reactions help create ATP and NADPH, light _____ use these to turn CO2 into organic molecules.

Light dependent reactions help create ATP and NADPH, light independent use these to turn CO2 into organic molecules.

What are the major differences between photophosphorylation and oxidative phosphorylation?

oxidative phosphorylation - occurs in mitochondria using chemical energy from nutrient oxidation to consume O2

photophosphorylation - occurs in chloroplasts using sunlight to split water and release oxygen

What is a photon?

a particle of light

The amount of energy a photon carries is determined by the _____.

wavelength

Describe the molecular structure of chlorophyll.

• porphyrin ring with central magnesium ion

• hydrophobic tail

• variations of functional groups

What is the function of the hydrophobic tail of chlorophyll?

anchors chlorophyll in the thylakoid membrane

Variations in the functional groups leads to what effect on chlorophyll?

leads to different types of chlorophyll (chlorophyll a and b)

What color wavelengths does chlorophyll typically absorb?

red and blue

What is the primary function of chlorophyll?

absorb light

Which of the following statements accurately describes a structural feature of

chloroplasts?

A) The stroma is the innermost compartment of the chloroplast, where the light-

dependent reactions of photosynthesis occur.

B) Thylakoids are membrane-bound structures within chloroplasts that contain

chlorophyll and are organized into stacks called grana.

C) The outer membrane of the chloroplast is impermeable, preventing the entry of any ions or small molecules.

D) Chloroplasts have a single, continuous membrane structure that separates their

internal environment from the cytosol.

B) Thylakoids are membrane-bound structures within chloroplasts that contain

chlorophyll and are organized into stacks called grana.

What is grana?

stacked, disc-like structures of thylakoid membranes found inside chloroplasts

The photosystems are organized to allow for _____ _____.

energy transfer

What are the two parts of photosystems?

the antenna and the reaction center

What is the antenna of a photosystem?

• the site of energy transfer

• contains the majority of chlorophyll pigments

• collects light and transfer the excitation energy to the reaction center complex

What is the reaction center of a photosystem?

• site of electron transfer

• has protein-associated chlorophyll dimer

True or False: the antenna transfers light-excited electrons to the reaction center.

False, it transfers the excitation energy not electrons

A high energy electron is transferred from the chlorophyll dimer to a carrier that becomes part of the electron transfer chain. This occurs in the _____.

reaction center of the photosystem

True or False: the reaction center converts light energy into chemical energy.

True

Photosystem II (PSII) transfers electrons to _____.

plastoquinone (Q)

Plastoquinone transfers electrons to ________ complex, this pumps protons into the thylakoid space. (PSII)

cytochrome b6-f

When light energy excites the chlorophyll special pain in PSII, an electron is passed to plastoquinone. The missing electron is replaced by an electron extracted from water by a ________.

water splitting enzyme

Once ___ electrons have been withdrawn from two water molecules, oxygen is released into the atmosphere. (PSII)

four

Photosystem I (PSI) receives electrons from _____, which comes from PSII after going through the electron transport chain.

plastocyanin

Electrons from PSII replace electrons lost by _____ in PSI.

excited chlorophyll special pair

PSI transfers high-energy electrons to ______, which brings them to an enzyme that produces NADPH.

ferredoxin

During non-cyclic photophosphorylation, the serial movement of electrons through ____ powers the production of ATP and NADPH.

the photosystems

Order the following for non-cyclic photophosphorylation.

A. The special pair of chlorophyll in PSI donates e- to ferredoxin (lost e- is replaced by e- donated by PSII via plastocyanin)

B. e- flow generates a proton gradient (through the cytochrome b6-f complex), which is used to produce ATP

C. e- is added to NADP+ by Ferredoxin NADP-reductase to make NADPH

D. The special pair of chlorophyll in PSII donates e- to plastoquinone (lost e- is replaced by splitting of water)

D. The special pair of chlorophyll in PSII donates e- to plastoquinone (lost e- is replaced by splitting of water)
A. The special pair of chlorophyll in PSI donates e- to ferredoxin (lost e- is replaced by e- donated by PSII via plastocyanin)

C. e- is added to NADP+ by Ferredoxin NADP-reductase to make NADPH

B. e- flow generates a proton gradient (through the cytochrome b6-f complex), which is used to produce ATP

Which photosystem is involved in cyclic photophosphorylation?

only PSI

What is produced during cyclic photophosphorylation?

ATP (does not produce NADPH and oxygen)

Cyclic photophosphorylation helps generate additional ATP that could be needed for the _____.

Calvin cycle

what happens if PSII is blocked during photosynthesis?

the light-dependent reactions of photosynthesis are severely disrupted, leading to a cascade of negative effects (happens with herbicides)

What is redox potential?

electron affinity

What two factors drive the direction of electron flow?

light and electron affinity (redox potentials)

The flow of electrons in the photosystems begins at ____, where photons excite electrons, raising them to a higher energy state.

PSII

For electron flow in photosystems, high energy electrons move through a series of proteins in the _____ and eventually reach ___. This is where they are re-energized by additional light absorption and used to reduce NADP+ → NADPH.

For electron flow in photosystems, high energy electrons move through a series of proteins in the thylakoid membrane and eventually reach PSI. This is where they are re-energized by additional light absorption and used to reduce NADP+ → NADPH.

Regarding light-harvesting complexes in plant chloroplasts, which of the following is FALSE?

A. They contain chlorophyll and other pigments.

B. They are found in both photosystem I and photosystem II.

C. They can carry out charge separation.

D. They do not contain special pair chlorophyll.

C. They can carry out charge separation.

What is the primary CO2 acceptor for carbon fixation?

Ribulose 1,5-bisphosphate (RuBP), a 5-carbon sugar

What is the first stable product of photosynthesis?

3-Phosphoglycerate, a 3-carbon acid

Carbon fixation is catalyzed by _____.

ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco)

What is the calvin cycle?

the carbon fixation cycle

Most plants reduce CO2 to sugars via the ______.

the carbon fixation cycle or C3 cycle (first product is a 3 carbon molecule)

What are the three distinct stages of the calvin cycle?

carboxylation, reduction, and regeneration

The net gain of the carbon fixation cycle is one molecule of ______.

glyceraldehyde 3-phosphate (G3P)

Most of glyceraldehyde 3-phosphate (G3P) is produced during the _____ phase is not used to make glucose but is recycled to regenerate ____.

Most of glyceraldehyde 3-phosphate (G3P) is produced during the reduction phase is not used to make glucose but is recycled to regenerate RuBP.

How many ATP and NADPH are consumed through the Calvin cycle to produce one molecule of glucose?

18 ATP and 12 NADPH

The photosynthetic carbon reduction cycle (aka Calvin cycle) reduces ___ to produce a _____.

The photosynthetic carbon reduction cycle (aka Calvin cycle) reduces

CO2 to produce a 3-carbon sugar.

The carboxylation of ___ molecules of RuBP leads to the net synthesis of ____ molecule of G3P, and the regeneration of the starting material.

the carboxylation of three molecules of RuBP leads to the net synthesis of one molecule of G3P, and the regeneration of the starting material.

each turn of the calvin cycle uses:

__ molecules of NADPH

__ molecules of ATP

2 molecules of NADPH

3 molecules of ATP

net synthesis of one G3P:

__ molecules of NADPH

__ molecules of ATP

6 molecules of NADPH

9 molecules of ATP

Chloroplasts often contain large stores of ____ and _____.

Chloroplasts often contain large stores of carbohydrates and fatty acids

The chloroplast’s inner membrane is impermeable to ___ and ___, which are used to make sugars

ATP and NADPH

The sugars made are either stored within the chloroplast or what other two things?

exported to the cytosol and converted to other metabolites OR broken down to generate ATP

Which of the following statements best represents the relationships between the light

reactions and the Calvin cycle?

A. The light reactions provide ATP and NADPH to the Calvin cycle, and the Calvin

cycle returns ADP, Pi, and NADP+ to the light reactions.

B. The light reactions provide ATP and NADPH to the carbon fixation step of the Calvin cycle, and the Calvin cycle provides water and electrons to the light reactions.

C. The light reactions supply the Calvin cycle with CO2 to produce sugars, and the

Calvin cycle supplies the light reactions with sugars to produce ATP.

D. The light reactions provide the Calvin cycle with oxygen for carbon fixation, and the

Calvin cycle provides the light reactions with sugars to produce ATP.

A. The light reactions provide ATP and NADPH to the Calvin cycle, and the Calvin

cycle returns ADP, Pi, and NADP+ to the light reactions.

What is the function of mitochondria?

ATP synthesis by oxidation phosphorylation

What is the function of the golgi apparatus?

protein and lipid modification and sorting

What is the function of the endoplasmic reticulum?

• rough — protein synthesis for distribution

• smooth — lipid synthesis

What is the function of an endosome?

sorting of endocytosed material

What is the function of a lysosome?

intracellular degradation

What is the function of the cytosol?

metabolic pathways, protein synthesis

What is the function of a peroxisome?

oxidative breakdown of toxic molecules and metabolism of lipids

What is the function of the nucleus?

contains nuclear genome, DNA/RNA synthesis

What is the function of the free ribosomes?

for protein synthesis in the cytosol

What is the function of the chloroplasts?

ATP synthesis and carbon fixation by photosynthesis

What organelles are contained in double membranes?

nucleus, mitochondria, chloroplasts

What is glycogen?

form of glucose that serves as energy storage

What are the three methods that a membrane enclosed organelle can import proteins?

1. gated transport — entering through pores (folded proteins)

2. transmembrane transport — enter via protein translocators (mostly unfolded proteins)

3. vesicular transport — move via transport vesicles that fuse with destination membranes (folded proteins)

Which method of importing proteins into membrane enclosed organelles requires energy?

all of them (gated, transmembrane, and vesicular)

How many amino acids make up a signal sequence?

3-60 amino acids

What is the function of a signal sequence?

directs a protein to the correct cellular location

What happens to the protein if there is no signal sequence?

protein stays in the cytosol

The signal sequence is typically found at what terminus?

N-terminus BUT it can also be internal or at the C-terminus depending on the organelle

Some of the signal sequences are ____ after import, this is common in the ER or mitochondria.

cleaved

In ____ and ____, the signal sequence is not cleaved and remains part of a mature protein.

nucleus and peroxisomes

The presence of what is crucial for the recognition and binding by import machinery for signal sequences?

hydrophobic, basic, and acidic residues

How does the structure of the nucleus affect the import of proteins?

proteins enter the nucleus via gated transport (through nuclear pores) → nuclear ports conduct extensive bidirectional traffic between the cytosol and the nucleus

The outer nuclear membrane is continuous with what organelle?

the ER membrane

True or False: all proteins that function within the nucleus must be actively transported into the nucleus.

True

The _______ forms a gate that selects which macromolecules and larger complexes enter/exit the nucleus.

nuclear pore complex

Folded proteins with nuclear localization signal are recognized by _______.

nuclear import receptors

The combined protein and receptor interact with ____. They also pass through a gel like meshwork of nuclear pore proteins.

cytosolic fibrils

What happens to the protein and receptor after they enter the nucleus.

• nuclear entry triggers the release of the protein

• receptor returns to cytosol via nuclear pore

Energy supplied from ____ drives nuclear transport.

GTP hydrolysis

What helps return the receptor to the cytoplasm (after the import of proteins)?

GTPase Ran

What is the GTPase activating protein?

Ran-GAP