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By the end of this section, you will be able to:
  • Explain the processes of glycolysis
  • Describe the pathway of a pyruvate molecule through the Krebs cycle
  • Explain the transport of electrons through the electron transport chain
  • Describe the process of ATP production through oxidative phosphorylation
  • Summarize the process of gluconeogenesis

Carbohydrates are organic molecules composed of carbon, hydrogen, and oxygen atoms. The family of carbohydrates includes both simple and complex sugars. Glucose and fructose are examples of simple sugars, and starch, glycogen, and cellulose are all examples of complex sugars. The complex sugars are also called polysaccharides    and are made of multiple monosaccharide    molecules. Polysaccharides serve as energy storage (e.g., starch and glycogen) and as structural components (e.g., chitin in insects and cellulose in plants).

During digestion, carbohydrates are broken down into simple, soluble sugars that can be transported across the intestinal wall into the circulatory system to be transported throughout the body. Carbohydrate digestion begins in the mouth with the action of salivary amylase    on starches and ends with monosaccharides being absorbed across the epithelium of the small intestine. Once the absorbed monosaccharides are transported to the tissues, the process of cellular respiration    begins ( [link] ). This section will focus first on glycolysis, a process where the monosaccharide glucose is oxidized, releasing the energy stored in its bonds to produce ATP.

Cellular respiration

This figure shows the different pathways of cellular respiration. The pathways shown are glycolysis, the pyruvic acid cycle, the Krebs cycle, and oxidative phosphorylation.
Cellular respiration oxidizes glucose molecules through glycolysis, the Krebs cycle, and oxidative phosphorylation to produce ATP.

Glycolysis

Glucose is the body’s most readily available source of energy. After digestive processes break polysaccharides down into monosaccharides, including glucose, the monosaccharides are transported across the wall of the small intestine and into the circulatory system, which transports them to the liver. In the liver, hepatocytes either pass the glucose on through the circulatory system or store excess glucose as glycogen. Cells in the body take up the circulating glucose in response to insulin and, through a series of reactions called glycolysis    , transfer some of the energy in glucose to ADP to form ATP ( [link] ). The last step in glycolysis produces the product pyruvate    .

Glycolysis begins with the phosphorylation of glucose by hexokinase to form glucose-6-phosphate. This step uses one ATP, which is the donor of the phosphate group. Under the action of phosphofructokinase, glucose-6-phosphate is converted into fructose-6-phosphate. At this point, a second ATP donates its phosphate group, forming fructose-1,6-bisphosphate. This six-carbon sugar is split to form two phosphorylated three-carbon molecules, glyceraldehyde-3-phosphate and dihydroxyacetone phosphate, which are both converted into glyceraldehyde-3-phosphate. The glyceraldehyde-3-phosphate is further phosphorylated with groups donated by dihydrogen phosphate present in the cell to form the three-carbon molecule 1,3-bisphosphoglycerate. The energy of this reaction comes from the oxidation of (removal of electrons from) glyceraldehyde-3-phosphate. In a series of reactions leading to pyruvate, the two phosphate groups are then transferred to two ADPs to form two ATPs. Thus, glycolysis uses two ATPs but generates four ATPs, yielding a net gain of two ATPs and two molecules of pyruvate. In the presence of oxygen, pyruvate continues on to the Krebs cycle (also called the citric acid cycle    or tricarboxylic acid cycle (TCA)    , where additional energy is extracted and passed on.

Questions & Answers

what is oedema
Nantumbwe Reply
i want abook about physiology including the vitamins
Belal
fluid retention in the body. (also spelt as edema) e.g. fluid retention in the lungs is called Pulmonary Edema). It can also happen as a result of Injury manifested as swelling.
Arif
can you give me an example of a tissue composed of few related types of cells
Theresa Reply
What is LMx1600
Mae Reply
the skeletal system includes all of the bones
All Reply
what is the bone not contain red bone marrow in medulla
Duha Reply
To know the part of human body
Sarah Reply
Anatomy refers to as structure of human body
Sarah
so is the macroscopic and microscopic the types of anatomy
Gloria Reply
is microscopic and macroscopic a type of anatomy
Gloria
yes
Maxine
yes
Yabsra
yes
Sarah
Please can someone explain three glands in endocrine system?
josh
.
Robin
can someone explain disease and the category
gege
type 2 is controled by diet
Chloe Reply
Diet and life style
Paias
Diet how? maybe eating food containing less sugar?
BTS
we must eat protein food to check our diet
Sarah
type 2 diabetes cannot be controlled by insulin so therefore your diet should be well balanced especially you shouldn't eat foods with high sugar level or stopping sugar at all so that the sugar content needed by your body will be provided by the balanced diet taken
Enada
what is hypotension
regina Reply
hypotension is when the blood pressure is less than 60/50
Mursal
hypo means low so it implies low blood pressure
Isaac
ok
Mursal
what is mild DKA
Mursal
mild diabetic ketoacidosis is when there is high level of sugar in the blood and the ketone bodies build up in the body ,is a type 1 which can lead to type 2
Isaac
what is the normal range for blood pressure?
BTS
120 over 80
Danielle
low blood pressure; opposite of high blood pressure which is hypertension
Regina
what if your a type 2 diabetic and you have no way to get meds due to no insurance what is some good over the counter medications to take?
Ashley
type 2 diabets is controlled by diet not meds.type 1 is contolled by insulin.
Chloe
type 1 diabets cant be controlled type 2 can be controlled.type 1 is worse than type 2 diabets.
Chloe
type 2 is purely a lifestyle disease, eat healthy, fresh, natural unprocessed real foods.
Danielle
sometime , we already eat diabetic diet than the results of blood sugar level not turn good , what is the reason ?
Muhammad
What is a "diabetic diet" though? Be specific. Juvenile diabetes and/or Type 1 diabetes is something that one can be born with, this needs medical diagnosis and intervention.
Danielle
what i mean by diabetic diet is we take fiber-rich food like vegetables,nut and also fish.
Muhammad
ok, no cause a doctor told me I needed metformin and my suger won't go under 300
Ashley
what is the difference between plasma and serum
Gloria Reply
Plasma contains fibrinogen while serum doesn't
Kateregga
plasma ----- fibrinogen = serum
Sneha
serum is blood plasma without fibrinogen or other clotting factors While blood plasma contains dissolved protein like fibrinogen,globulin, and albumin), glucose, clotting factors,mineral ions like Na2+,Cl-1,hormones and carbon dioxide
Prince
In what time stomach empty it's content in to doudemun? what is chyme?
Sneha Reply
write the chemical and mechanical digestion which occurs in stomach?
Sneha
Does absorption take place in stomach? what are absorption in the stomach by which cell?
Sneha
Chemical digestion---Mixtures of the food with the gastric acid Mechanical digestion--- churning of the food in the stomach making it become more involved into chyme
Mercy
absorption takes place in the small intestine because of the presence of the villi
Enada
name the muscles supplied redina nerve
Appu Reply
mechanism of hormone releasing by gland
said Reply
why is muscle tissue not considered to be a type of connective tissue?
Ezel Reply
A Skeletal muscles consist of numerous muscles cells called Muscle Fibers . Three layers of connective tissues surrounded these fibers to make the muscles tissues
Manisha
that's wny connective tissues is not considered as muscles fibers
Manisha
there are 4 types of tissues : epithelial, connective tissue, nervous tissue and muscle tissue, each one has its own properties. The main function of connective tissue is nutrition, it supplies nutrientes to epithelial tissues that are responsible for protection.
Ariete
Muscle tissue has properties that allow movement, the function here is movement and not nutrition like connective tissue.
Ariete
In what time stomach empty it's content in to doudemun?
Sneha
write the chemical and mechanical digestion which occurs in stomach?
Sneha
Does absorption take place in stomach? what are absorption in the stomach by which cell?
Sneha
Does absorption take place in stomach? what are the absorption in the stomach by which cell?
Sneha
mechanism of hormone controlling releasing by gland
said
please can someone explain renin angiotensin aldosteron system for me
okolie
name the joint present between epichysif and diachysif
JAYKISHAN Reply
what is arteries
JAYKISHAN
oxygenated blood carrying vessels
Karanpreet
I think oxygenated blood carrying pulmonary vein
Omaryare
ya this stetment is right 4 pulmonary vein carrying the oxygenated blood
Sneha

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Source:  OpenStax, Anatomy & Physiology. OpenStax CNX. Feb 04, 2016 Download for free at http://legacy.cnx.org/content/col11496/1.8
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