Final: Chapter 14

Question 1

loss of testosterone

Answer 1

• Testosterone receptor missing
• Androgen insensitivity syndrome (AIS)
  
  • XY, genetically male, develop female

Question 2

oxidative phosphorylation

Answer 2

2 stages: one sets up an electrochemical proton gradient, the other uses that gradient to generate ATP

Question 3

oxidative phosphorylation stage 1

Answer 3

• high-energy e- from the oxidation of food molecules from sunlight, or from other sources are transferred along a series of electron carriers—called an electron-transport chain—embedded in the membrane
• e-transfers release energy that is used to pump protons, derived from the water that is ubiquitous in cells, across the membrane and thus generate an electrochemical proton gradient
• ion gradient across a membrane is a form of stored energy that can be used to do useful work when the ions are allowed to flow back across the membrane down their electrochemical gradient

Question 4

stage 2 of oxidative phosphorylation

Answer 4

• protons flow back down their electrochemical gradient through a protein complex called ATP synthase(catalyzes the energy-requiring synthesis of ATP from ADP and inorganic phosphate (Pi))
• This ubiquitous enzyme functions like a turbine, permitting the proton gradient to drive the production of ATP

Question 5

chemiosmotic coupling

Answer 5

• When it was first proposed, this mechanism for generating energy was called the chemiosmotic hypothesis, because it linked the chemical bond-forming reactions that synthesize ATP (“chemi-”) with the membrane transport processes that pump protons(osmotic)
• chemiosmotic coupling lets cells harness energy of e- transfers in same way energy stored in battery lets u do work

Question 6

mitochondria

Answer 6

• produce bulk of cell’s ATP(without mito, cells would rely on inefficient glycolyis for ATP)
• adaptable and can adjust their location, shape, and number to suit the needs of the cell
• some are fixed and supply ATP to direct site
• others, mito fuse to form elongated, dynamic tubular networks, which are throughout cytoplasm
  
  • break apart by fission and fuse back together

Question 7

structure of mitochondria

Answer 7

• outer and inner membrane plus internal space called matrix and narrower intermembrane space(each has unique proteins)
• outer membrane:
  
  • lots of porin(forms wide channels in lipid bilayer)
  • permeable
  • intermembrane space is chemically equivalent to cytosol bc of small molecs and inorganic ions
• inner membrane:
  
  • impermeable except with specific membrane transport proteins
  • site of oxidative phosphorylation, contains e- transport chain proteins(proton pumps), and ATP synthase for ATP production
  • contains transport proteins that allow entry of selected small molecs that will be oxidized into matrix
  • forms infoldings(cristae) -inc SA
    
    • mitochondrial matrix contains only molecules that are selectively transported into the matrix across the inner membrane(highly specialized)

Question 8

citric acid cycle makes high energy e- used in ATP production

Answer 8

• burning food = ATP
• activated carriers from catabolism = high energy e-
• pyruvate can enter mitochondrial intermembrane space through porins, where they become acetyl CoA
• citric acid cycle
• some energy is saved in form of high energy e-, held by NADH and FADH2
  
  • these donate e- to e- transport chain

Question 11

electron transport chain: respiratory enzyme complexes

Answer 11

• 3 respiratoyry enzyme complexes(in order in which they receive e-)
  
  • NADH dehydrogenase complex(catalyst)
    
    • accepts e- from NADH
  • cytochrome c reductase complex
  • cytochrome c oxidase complex
• as e- move thru complexes,protons pump from mitochondrial matrix to intermembrane space
• energetically favorable

Question 12

electron transport chain proton gradient

Answer 12

• pumping of protons makes H+ gradient(aka pH gradient)
  
  • higher pH in matrix than intermembrane
• pumping protons generates voltage gradient(membrane potential) across inner membrane
  
  • H+ flow outside makes intermembrane side more pos

Question 13

ATP synthase

Answer 13

• drives synthesis of ATP from ADP and Pi
• Catalyzes the phosphorylation of ADP
• it is attached by a central stalk to a transmembrane H+ carrier
• The passage of protons through the carrier causes the carrier and its stalk to spin rapidly
• As the stalk rotates, it rubs against proteins in the stationary head, altering their conformation and prompting them to produce ATP
• ATP synthase produces more than 100 molecules of ATP per second—3 molecules of ATP per revolution

Question 14

ATP synthase in reverse

Answer 14

• use ATP as energy to pump protons against gradient

Question 15

electrochemically proton gradient in mitochondria

Answer 15

• drives formation of ATP AND transport selective metabolites across mitochondrial membrane

Question 16

The Rapid Conversion of ADP to ATP in Mitochondria Maintains a High ATP/ADP Ratio in Cells

Answer 16

• ADP molecules—produced by hydrolysis of ATP in the cytosol—are rapidly drawn back into mitochondria for recharging, while the bulk of the ATP molecules produced in mitochondria are exported into the cytosol
• ATP can go out of mitochondria and back in as ADP in 1 min

Question 17

Cellular respiration efficiency

Answer 17

• 1 NADH = 2 ATP
• The NADH molecules produced in the mitochondrial matrix during the citric acid cycle pass their highenergy electrons to the NADH dehydrogenase complex—the first complex in the chain. As the electrons pass from one enzyme complex to the next, they promote the pumping of protons across the inner mitochondrial membrane at each step along the way
• 1 FADH2 = 1.5 ATP(bc they enter further down chain
• almost 50% of energy that could be realeased by burning sugars is actually captured

Question 18

chloroplasts + photosynthesis overview

Answer 18

• chloroplasts contains light-capturing pigments such as the green pigment chlorophyll
• most plants, leaves are the major sites of photosynthesis.
• Photosynthesis occurs only during the daylight hours, producing ATP and NADPH.
• ATP and NADPH can then be used, at any time of day, to convert CO2 into sugar inside the chloroplast—a process called carbon fixation

Question 19

chloroplast structure

Answer 19

• resemble mitochondira
  
  • has highly permeable outer membrane and less perm inner membrane(holds proteins)
• inner membrane surrounds large space called stroma(equiv of mitochondrial matrix) which contains metabolic enzymes
• light-capturing systems, electron-transport chain, and ATP synthase that produce ATP during photosynthesis are all contained in the thylakoid membrane
  
  • forms a set of flattened disclike sacs(thylakoids)
  • stack = grana
  • thlyakoid space: space inside each thylakoid is thought to be connected with that of other thylakoids, creating a third internal compartment

Question 20

photosynthesis stage 1

Answer 20

• equiv to ox phosphorylation
• 1) e- transport chain in thylakoid membrane harnesses energy to pump protons to thylakoid space
  
  • results in proton gradient that that drives synthesis of ATP by ATP synthase
  • diff from ox phos bc e- coming in come from 1 molec of chlorophyll from sunlight
    
    • these are called light rxns
  • diff bc the high E e- end up with NADP+ to produce NADPH (in ox phos it goes to O2)

Question 21

photosynthesis stage 2

Answer 21

1. ATP and NADPH from stage 1 drive manufacture of sugars from CO2
   
   1. these are carbon fixation rxns called fark rxns
   2. begin in chloroplast stroma where they generate a three-carbon sugar called glyceraldehyde 3-phosphate
      
      1. this sugar is moved to cytosol where it produces sucrose and other organic molecs

Question 22

how does chlorophyll absorb energy of sunlight

Answer 22

• e- in chlorophyll are distributed in a decentralized cloud around molecs light absorbing porphyrin ring
• when light of right wavelngth(blue/red bc they absorb green poorly) hits chlorophyll, it excites these e- into an unstable state, so chloropyll wants to remove excess energy to become stable again
• instead of releasing energy, chlorophyll converts light E into E usable for cell bc they associate with photosynthetic proteins in thylakoid membrane

Question 23

how does excited chlorophyll funnel E into rxn center

Answer 23

• photosystems: large multiprotein complexes that hold chlorophyll
  
  • each photosystem contains antenna complexes that capture light energy
    
    • each has hundreds of cholorophyll molecs
      
      • one captures light and passes it to next along chain
      • eventually it encounters a chlorophyll dimer called the special pair which holds its e- at lower R so it can trap the light energy
  • and a rxn center that converts ligh E into chemical E
    
    • the special pair is actually part of the rxn center
    • evolved >3 bil years ago
    • special pair is right next to a set of e- carriers that will accept a high E e- from light
  • as soon as high E e- is handed off, special pair becomes + charged and e- carrier becomes -
• overall, creates a charge separation that sets in motion of e- flow from rxn center to an e- transport chain

Question 24

a pair of photosystems allow generation of ATP and NADPH

Answer 24

• first photosystem is called photosystem 2
  
  • absorbs light E, rxn center passes e- to mobile e- carrier(plastoquinone)
  • pastoquinone transfers high E e- to proton pump which uses movement of e- to generate proton gradient
  • gradient drives ATP production by ATP synthase in thlakoid membrane
• photosystem 1(step 2)
  
  • captures E from sun, passes high E ei to a diff e- carrier, which brings them to enzyme that uses them to reduce NADP+ to NADPH
• OVERALL: prodyces ATP and NADPH to use in photosynthesis stage 2

Question 25

how does photosystem 2 generate oxygen

Answer 25

• when mobile e- carrier removes an e- from rxn center(in b oth photosystems), it leaves behind a pos charged chlorophyll special pair (OH NO!)
• missing e- must be replaced to reset system and let photosyntehsis proceed
  
  • photosystem 2: water splitting enzyme steals an e- from water
    
    • has cluster of manganese that takes 4 e-(one at a time) and replaces lost e- (SO, O2 is released)
  • while waiting for 4 e-, this ensures no partly oxidized waters are released as dangerous chemicals
    
    • cytochrome c uses reverse(brings e- to O2 to release H2O)
• Essentially all of earth’s O2 comes from photosystem 2

Question 26

where does photosystem 1 get its missing e- from?

Answer 26

• photosystem 2 helps out:
  
  • the chlorophyll special pair in photosystem 1 accepts final e- from photosys 2s e- transport chain
    
    • e- removed from water by photosys 2 are passed thru proton pump to mobile e- carrier(plastocyanin)
    • plastocyanin brings these e- to photosys 1 to replace missing e-
    • when light is again absorbed by photosys 1, the e- is boosted to very high E and reduces NADP+ to NADPH

Question 27

carbon fixation

Answer 27

• light rxns of photosynthesis generate ATP and NADPH in chloroplast stroma, but it can’t get to inner membrane(its impermeable)
• SO, ATP and NADPH are used w/in stroma to produce sugars
  
  • sugars are moved to chloroplast inner membrane by specific carrier proteins
    
    • this occurs during dark rxns(stage 2 of photosynth)
    • dark rxn = carbon fixation
• overall, energetically favorable bc its continuous supply of E rich ribulose 1,5 bisphosphate is fed into it
  
  • ATP and NADPH from light rxns provide E and reducing power to replace ribulose 1,5 bisphosphate

Question 28

carbon fixation cycle/calvin cycle

Answer 28

• CO2 from atmosphere is attached to ribulose 1,5 bisphosphate
  
  • yields 2 molecs of 3 bisphosphate
• rxn is catalyzed in stroma by large enzyme called ribulose bisphosphate carboxylase(Rubisco)
  
  • Rubisco is a v slow enzyme :( only 3 molecs of substrate per sexond rather than typical 1000
  • to make up for this plants keep OD Rubisco on hand
  • more than 50% of chloroplast’s proteins are Rubisco(it is the most abundant protein on Earth)
• production of carbs from CO2 and H2O is E unfavorable, fixation of CO2 catalyzed by Rubisco is E favorable

Question 29

sugars from carbon fixation cycle: what happens to them?!

Answer 29

• these sugars can be stored as starch or consumed to produce ATP
• glyceraldehyde 3-phosphate use dependson needs of plants
• during periods w/ a ton of photsynthesis happening, it stays in chloroplast stroma(as large granules)and is converted to starch
  
  • the strach is a large polymer of glucose and serves as a carb reserve
  • animals that eat plants get this(yum)
• others are converted to fat in stroma(stored as fat droplets) to serve as energy reserve
  
  • ​at night, the stored starch and fat are broken down to sugars and fatty acids
  • then expoerted to cytosol to support plant metbolism
  • some exported sugar enters glycolytic pathway where it is converted to pyruvate
  • the pyruvate(and fatty acids) can enter plant cell mitochondria and be fed into citric acid cycle(ultimately leads to production of ATP by ox phos)
    
    • this ATP is used like in animals to power metabolic rxns
• glyceraldehyde 3 phosphate exported from chloroplasts into cytosol can also be converted into other metabolites(EX: disaccharide sucrose)
  
  • sucros is the glucose of plants
  • sucrose goes thru leaves like glucose goes thru blood