Download Biology 123 SI- Dr. Raut`s Class Session 11

Biology 123 SI- Dr. Raut’s Class
Session 11- 02/23/2015
1. Why is the amount of ATP formed so variable? (Several answers. List them all)
Pyruvate actually requires active transport to get into the mitochondria which means it uses some
ATP. NADH that is produced in glycolysis cannot cross the mitochondria’s membrane and must
use a shuttle system and give its electrons to either an FAD or NAD+ which are already inside
the mitochondrial matrix. FADH2 gives its electrons to complex two instead of one which means
it produces less ATP than NADH. It is not known exactly how many protons are required to
cause ATP synthase to make ATP, and it may vary.
2. What is the limiting factor in fermentation? Explain why this is.
The rate limiting fact in fermentation is NAD+. If NAD+ is not present, then oxidation cannot
happen and the process cannot proceed. Since the electrons in NADH cannot be given to the
electron transport chain due to the lack of oxygen, the electrons must be given to something in
order for NAD+ to be regenerated so glycolysis can occur again. Therefore, NADH gives these
electrons back to an organic molecule.
3. What are the two types of fermentation? Explain both.
The two types of fermentation are lactic acid fermentation and alcohol fermentation. In both
reactions, glycolysis proceeds as usual producing pyruvate. In lactic acid fermentation, pyruvate
directly accepts the electrons from NADH and forms lactate. In alcohol fermentation, CO2 comes
out of pyruvate, forming acetaldehyde. Acetaldehyde then accepts the electrons forming alcohol.
4. True or false: Organisms are either aerobic or anaerobic, but they cannot be both.
False. Many organisms can only live in either aerobic or anaerobic conditions; for example,
obligate anaerobes can only live in anaerobic conditions. However, some organisms are
facultative anaerobes and can function in both aerobic and anaerobic conditions. Facultative
anaerobes include yeasts and many bacteria, and these organisms will perform fermentation
when oxygen is not present and aerobic respiration when oxygen is present.
5. What are the processes that break down proteins and fats into products that can enter into
cellular respiration?
While cellular respiration is typically taught using glucose, many different products can go into
cellular respiration at different points in the cycle. Proteins will go through a process called
deamination in which the amino groups are removed. After deamination, the broken down amino
acids can enter cellular respiration in many different places. Triglycerides go through a process
called beta oxidation. Beta oxidation breaks the fat into two carbon fragments which will enter
into cellular respiration as acetyl CoA. Beta oxidation also produces NADH and FADH2 which
is one reason why fats are worth more energy than sugars and proteins.
6. What is the main rate-determining enzyme in glycolysis? What stimulates it? What inhibits it?
The main rate-determining enzyme in glycolysis is phosphfructokinase. ATP and citrate both
inhibit phosphofructokinase. AMP stimulates phosphofructokinase.
7. True or false: Plants are the only organisms that perform photosynthesis.
False. Lots of organisms including different bacteria, protists, and alga perform photosynthesis.
8. Draw out the balanced equation for photosynthesis. What type of a reaction is this?
6 CO2 + 12 H2O + Light energy → C6H12O6 + 6 O2 + 6 H2O
This is an endergonic reaction. It requires light energy to be put into the reaction in order for it to
proceed.
9. Photosynthesis is a redox reaction. What is oxidized, and what is reduced?
CO2 is reduced. H2O is oxidized.
10. What are the two parts of photosynthesis? Where do they occur? What happens in each?
The two parts of photosynthesis are the light reactions and the Calvin Cycle. The light reactions
occur in the thylakoid membrane and require light in order to proceed. In the light reactions H2O
splits and O2 is produced, NADPH is produced, and ATP is produced. The Calvin Cycle is light
independent and occurs in the stroma. The Calvin Cycle relies on the ATP and NADPH that
were produced in the light reactions and is the part in which sugar is synthesized.
11. What in chloroplasts absorbs light?
Color pigments absorb light. Chloroplasts have chlorophyll a, chlorophyll b, and accessory
pigments called the carotenoids. These pigments will absorb certain ranges of light in the visible
light spectra. The color that they appear to be is actually the color that they reflect not what they
absorb (chlorophyll actually does not absorb green light). Pigments absorb photons, which
causes electrons to become excited and heat and the photon is released as the electron falls back
down to the ground state.