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By the end of this section, you will be able to:
  • Describe the overall result in terms of molecules produced in the breakdown of glucose by glycolysis
  • Compare the output of glycolysis in terms of ATP molecules and NADH molecules produced

You have read that nearly all of the energy used by living cells comes to them in the bonds of the sugar, glucose. Glycolysis is the first step in the breakdown of glucose to extract energy for cellular metabolism. Nearly all living organisms carry out glycolysis as part of their metabolism. The process does not use oxygen and is therefore anaerobic    . Glycolysis takes place in the cytoplasm of both prokaryotic and eukaryotic cells. Glucose enters heterotrophic cells in two ways. One method is through secondary active transport in which the transport takes place against the glucose concentration gradient. The other mechanism uses a group of integral proteins called GLUT proteins, also known as glucose transporter proteins. These transporters assist in the facilitated diffusion of glucose.

Glycolysis begins with the six carbon ring-shaped structure of a single glucose molecule and ends with two molecules of a three-carbon sugar called pyruvate    . Glycolysis consists of two distinct phases. The first part of the glycolysis pathway traps the glucose molecule in the cell and uses energy to modify it so that the six-carbon sugar molecule can be split evenly into the two three-carbon molecules. The second part of glycolysis extracts energy from the molecules and stores it in the form of ATP and NADH, the reduced form of NAD.

First half of glycolysis (energy-requiring steps)

Step 1. The first step in glycolysis ( [link] ) is catalyzed by hexokinase, an enzyme with broad specificity that catalyzes the phosphorylation of six-carbon sugars. Hexokinase phosphorylates glucose using ATP as the source of the phosphate, producing glucose-6-phosphate, a more reactive form of glucose. This reaction prevents the phosphorylated glucose molecule from continuing to interact with the GLUT proteins, and it can no longer leave the cell because the negatively charged phosphate will not allow it to cross the hydrophobic interior of the plasma membrane.

Step 2. In the second step of glycolysis, an isomerase converts glucose-6-phosphate into one of its isomers, fructose-6-phosphate. An isomerase    is an enzyme that catalyzes the conversion of a molecule into one of its isomers. (This change from phosphoglucose to phosphofructose allows the eventual split of the sugar into two three-carbon molecules.).

Step 3. The third step is the phosphorylation of fructose-6-phosphate, catalyzed by the enzyme phosphofructokinase. A second ATP molecule donates a high-energy phosphate to fructose-6-phosphate, producing fructose-1,6- bi sphosphate. In this pathway, phosphofructokinase is a rate-limiting enzyme. It is active when the concentration of ADP is high; it is less active when ADP levels are low and the concentration of ATP is high. Thus, if there is “sufficient” ATP in the system, the pathway slows down. This is a type of end product inhibition, since ATP is the end product of glucose catabolism.

Questions & Answers

phenotype is your big head
Amagiya Reply
The phenotype is the physical appearance or things you can see. Or the traits expressed by ones DNA.
what is a dichotomous key
Moses Reply
explain the role of
Dichotomous key : Is the key that is use to classify or group an organism base on their common features
an amoeba is what kind of cellular organism?
Mercy Reply
It is a protizoa with bilayer membrane bound organelles. Therefore it is eukaryotic.
what is amoeba
amoeba is a unicellular organisms. Therefore it is made u of only one call.
what is phenotype
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daigram of connective tissue
Yunusa Reply
what is polarization
Finda Reply
What is appendicular
relating to or denoting an appendage or appendages.
Homeostasis definition
Ben Reply
can be defined as a steady of internal environment
wat is active transport
Roster Reply
The movement of molecules from the region of lower concentration to the region of higher concentration
what are derived quantities
Esther Reply
Derived quantities are quantities that are calculated from two or more measurements. Derived quantities cannot be measured directly. They can only be computed.
name two types of acid
Grace Reply
Hydrochloric acid and tetraoxoshulphate(VI) acid
melic acid and aspartic acid
sulphuric acid, hydrochloride acid
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Castro Reply
Tar which causes lung cancer
what is osmosis
Tinashe Reply
explanation of osmosis
movement of water particles from a region of high concentration to a region of low concentration across a semi permeable membrane
movement ofwater particle from aregion
what is respiration
Favour Reply
organisms and their respiratory organs
Osmosis.. An example of Osmosis is when red blood cells, which have a high concentration of protein and salt, are plaeed in a lower concentration fluid like water the water will rush into the red blood cells.
boafo Reply
You're asked for the Definition, not yet an example. Definition first,before example, o.k?
osimosis is the movement of watermolecules from they region of high concetration to the region of lower concertation

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Source:  OpenStax, Biology. OpenStax CNX. Feb 29, 2016 Download for free at http://cnx.org/content/col11448/1.10
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