fermentation and photosynthesis, Schemes and Mind Maps of Microbiology

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Fermentation

Photosynthesis

Lecture 6

 Cells obtain most of their Energy by membrane-based mechanism:

In yeast

 In Yeast, pyruvic acid is decarboxylated and reduced by NADH to form a molecule of carbon dioxide and one of ethanol.  (^) C 3

H

4

O

3

+ NADH + H

→ CO 2

+ C

2

H

5

OH + NAD

 This accounts for the bubbles and alcohol in, for examples, beer and champagne. The process is called alcoholic fermentation.  NAD is recycled  (^) How many ATPs?  (^) Aerobic or anaerobic?

 The complete pathway, including Glycolysis and the re-oxidation of NADH, is called fermentation.  (^) Lactate Dehydrogenase catalyzes reduction of the pyruvate to lactate, as NADH is oxidized to NAD

.  (^) Lactate , in addition to being an end-product of fermentation, serves as a mobile form of nutrient energy , and possibly as a signal molecule in mammalian organisms

Fermentation and Oxygen

 Glycolysis can occur with or without oxygen. In the presence of oxygen, glycolysis is the first stage of cellular respiration.  (^) Without oxygen, glycolysis allows cells to make small amounts of ATP. This process is called fermentation.  (^) Anaerobic organisms lack a respiratory chain. They must reoxidize NADH produced in Glycolysis through some other reaction, because NAD + is needed for the Glyceraldehyde-3- phosphate Dehydrogenase reaction. Usually NADH is reoxidized as pyruvate is converted to a more reduced compound.

 Skeletal muscles ferment glucose to lactate during exercise, when the exertion is brief and intense.  (^) Lactate released to the blood may be taken up by other tissues, or by skeletal muscle after exercise, and converted via Lactate Dehydrogenase back to pyruvate, which may be oxidized in Krebs Cycle or  (in liver) converted to back to glucose via gluconeogenesis.  (^) Lactate serves as a fuel source for cardiac muscle as well as brain neurons.

How many ATPs?

 Fermentation Pathway, from glucose to lactate:  (^) Anaerobic catabolism of glucose yields only 2 high energy bonds of ATP.  (^) Liver cells have major roles in metabolism, including maintaining blood levels of various nutrients such as glucose.

 Glucokinase allows the liver to store glucose as glycogen in the fed state when blood [glucose] is high.  (^) The liver enzyme Glucose-6-phosphatase catalyzes hydrolytic release of Pi from glucose-6- phosphate. Thus glucose is released from the liver to the blood as needed to maintain blood [glucose].  Both found in liver but not in most other body cells, allow the liver to control blood [glucose].

Photosynthesis

 The best known form of photosynthesis is the one carried out by higher plants and algae , as well as by cyanobacteria and their relatives, which are responsible for a major part of photosynthesis in oceans.  (^) All these organisms convert CO 2 to organic material by reducing this gas to carbohydrates in a rather complex set of reactions.  Electrons for this reduction reaction ultimately come from water, which is then converted to oxygen and protons.

 Energy for this process is provided by light , which is absorbed by pigments (primarily chlorophylls and carotenoids).  (^) Chlorophylls absorb blue and red light and carotenoids absorb blue-green.

Photosynthesis and Chloroplasts

 (^) Chloroplasts are found only in photosynthetic protists and plant cells. Internal membranes called thylakoids which, in plants, form stacks called grana. The thylakoids contain the proteins and other molecules responsible for light capture. The dark reactions of photosynthesis take place in the matrix, called the stroma