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Glycolysis and Fermentation: Metabolic Pathways for Energy Extraction from Glucose, Exercises of Enzymes and Metabolism

Word of Life Bible InstituteEnzymes and Metabolism

An overview of glycolysis and fermentation, two ancient metabolic pathways used by organisms to extract energy from glucose. Glycolysis is the first step in energy extraction and does not require oxygen, while fermentation is used in the absence of oxygen. The mechanisms of these processes, their net energy yield, and the role of nadh and atp. It also discusses the differences between homolactic acid fermentation and alcoholic fermentation.

What you will learn

  • How does glycolysis contribute to the net energy yield from glucose?
  • What are the differences between homolactic acid fermentation and alcoholic fermentation?
  • What are the three main metabolic pathways used by bacteria to extract energy from glucose?

Typology: Exercises

2021/2022

Uploaded on 09/12/2022

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Chapter 5 Metabolism:
Glycolysis & Fermentation
Dr. Amy Rogers
Office Hours: Mondays & Wednesdays 9-10 AM
Sequoia 530
Some figures taken from Krogh Biol ogy: A Guide to the Natural World
The material presented in this lecture will be tested on E xam #2.
Exam #1 is Wednesday! Please bring a Scantron form.
Bacterial Metabolism:
3 pathways
to extract energy from glucose
• Glycolysis
• Fermentation
• Aerobic Respiration
(Krebs cycle, electron transport, oxidative phosphorylation)
Glycolysis
•Ancient metabolic pathway: 3.5 BYA…before
earth’s atmosphere had oxygen in it
• The first steps of energy extraction from glucose
• Does NOT require oxygen
• Autotrophs & heterotrophs, aerobes &
anaerobes all do it
• Net energy yield is small: 2 ATP per glucose
Glucose is a 6 carbon sugar
Products of glycolysis:
•Two 3-carbon molecules: pyruvic acid (x2)
•2 reduced NADH electron carriers: from 2 NAD+
•2 (net) ATP: from 2 ADP + 2 Pi
1. Two phosphates from ATP are added to each glucose molecule
2. Glucose is isomerized into another 6 carbon sugar, fructose
Net energy yield: -2 ATP (2 ATP have been consumed to ADP + Pi)
Glycolysis 1: Substrate level phosphorylation
Kinase
Kinase
Phosphate transfers are common
Kinase: generic name for any enzyme that
adds a phosphate group to something
Phosphatase: generic name for any enzyme that
cleaves a phosphate group from something
{These are opposite activities}
pf3
pf4

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Download Glycolysis and Fermentation: Metabolic Pathways for Energy Extraction from Glucose and more Exercises Enzymes and Metabolism in PDF only on Docsity!

Chapter 5 Metabolism :

Glycolysis & Fermentation

Dr. Amy Rogers

Office Hours: Mondays & Wednesdays 9-10 AM Sequoia 530 Some figures taken from Krogh Biology: A Guide to the Natural World

The material presented in this lecture will be tested on Exam #2.

Exam #1 is Wednesday! Please bring a Scantron form.

Bacterial Metabolism:

3 pathways

to extract energy from glucose

• Glycolysis

• Fermentation

• Aerobic Respiration

(Krebs cycle, electron transport, oxidative phosphorylation)

Glycolysis

• Ancient metabolic pathway: 3.5 BYA…before

earth’s atmosphere had oxygen in it

• The first steps of energy extraction from glucose

• Does NOT require oxygen

• Autotrophs & heterotrophs, aerobes &

anaerobes all do it

• Net energy yield is small: 2 ATP per glucose

Glucose is a 6 carbon sugar

Products of glycolysis:

•Two 3-carbon molecules: pyruvic acid (x2)

•2 reduced NADH electron carriers: from 2 NAD+

•2 (net) ATP : from 2 ADP + 2 Pi

  1. Two phosphates from ATP are added to each glucose molecule
  2. Glucose is isomerized into another 6 carbon sugar, fructose

Net energy yield: -2 ATP (2 ATP have been consumed to ADP + Pi )

Glycolysis 1: Substrate level phosphorylation

Kinase

Kinase

Phosphate transfers are common

Kinase : generic name for any enzyme that

adds a phosphate group to something

Phosphatase : generic name for any enzyme that

cleaves a phosphate group from something

{These are opposite activities}

Why does it take ATP to make ATP?

1. Phosphorylation of glucose “raises its energy

level so it can participate in subsequent

reactions (like the rock pushed out of the

depression atop the hill).”

2. Phosphorylated sugars are trapped inside the

cell (plain glucose freely moves in & out)

Glycolysis 2: Splitting

  • 6 carbon sugar (fructose) is split into two 3-carbon molecules
  • Each molecule gets one of the phosphate groups
  • The molecules are not identical
  • One molecule is isomerized (rearranged) so the two 3-carbon molecules become identical : glyceraldehyde 3-phosphate

Glycolysis 3: Rearrangements & energy capture

• In this series of enzyme-catalyzed reactions,

energy is first extracted from the food (glucose)

• The energy is captured in two forms:

  • NAD+ is reduced to NADH (one per 3 carbon unit) Carries energy as “reducing power” (more on this later)
  • ADP+Pi ATP (two per 3 carbon unit)

(Substrate-level phosphorylation)

» The inorganic phosphate (Pi ) comes from the phosphorylated 3 carbon units

Remember: All this happens x per glucose as each 6 carbon glucose yields two 3 carbon G3P molecules

End product: pyruvic acid (x2)

**1. NAD+ reduced to NADH

  1. ATP produced from ADP+P** (^) i

Note how the products of glycolysis

(pyruvic acid, or pyruvate)

are oxidized relative to

the initial substrate (glucose)

Carbo loading & glycolysis

  • Each reaction in glycolysis is catalyzed by an enzyme
  • Enzyme activity is usually regulated in some way
  • Part of the reason why “Carbo loading” (eating a great deal of carbohydrates before an athletic endurance event) works may be that it induces expression of glycolytic enzymes. - More enzyme = faster catalytic activity = faster glycolysis

Homolactic acid fermentation

  • Simplest pathway, one step conversion of pyruvic acid
  • Only one ( homo- ) product: lactic acid. No gas produced
  • Lactobacilli ( some cheeses); streptococci ; also mammalian muscle cells

Look! No ATP made!

Alcoholic Fermentation

2 steps; CO 2 gas & ethyl acohol are products Rare in bacteria, common in yeast Bread & wine

Look! No ATP made!

Other fermentation pathways

• Performed by a great variety of microbes

• We’ll test for many pathways in lab

  • generally by looking for end products or intermediates

• A huge range of products can be produced

• Many have commercial utility; others are

involved in disease, food spoilage, etc.

Terminal electron acceptors

• The goal of fermentation is to oxidize NADH

• Something must be reduced (the electrons must

go somewhere)

• Organic compounds (for example, lactic acid & ethyl

alcohol) are the terminal electron acceptors in

fermentation pathways

Later: how using OXYGEN as the terminal electron acceptor is a MUCH better deal!!!

Just to remind me to tell you: Table 6.6 has a discussion of the TSI test