Energy Reactions

Question 1

Why do cells metabolise nutrients?

Answer 1

Energy for cell function, building block molecules, organic precursor molecules and biosynthetic reducing power

Question 2

Where do cell nutrients in the blood come from?

Answer 2

Diet, synthesis in the body and released from storage in body tissues

Question 3

What are the main characteristics of a catabolic pathway?

Answer 3

Oxidative, release H+ (reducing power), releases free energy (some conserved as ATP), produces intermediary metabolites

Question 4

What are the main characteristics of an anabolic pathway?

Answer 4

Reductive, use H+. Use intermediary metabolites and energy (ATP) produced by catabolism to drive synthesis of important cell components

Question 5

Why do cells need a continuous supply of energy?

Answer 5

Resist entropy, grow, activity of tissues, homeostasis and biosynthesis

Question 6

What is the chemical reaction that occurs in muscles to produce creatine phosphate?

Answer 6

Creatine + ATP —> Creatine Phosphate + ADP (catalysed by creatine kinase)

Question 7

Describe the structure of a monosaccharide

Answer 7

Contain trioses, pentoses and hexoses. Aldose or ketose. Ring structures with a hemiacetal ring. Chiral C (anomeric-C) can be alpha or beta

Question 8

Describe the structure of a disaccharide

Answer 8

Formed by condensation of two monosaccharides, water is eliminated. In diet - sucrose (glucose and fructose), lactose (glucose and galactose) and maltose (2 x glucose)

Question 9

Describe the structure of a polysaccharide

Answer 9

Monosaccharides linked by glycosidic bonds. Glycogen, starch, cellulose etc

Question 10

How are dietary polysaccharides digested?

Answer 10

Hydrolysed by glycosidase enzymes. Releases glucose, maltose and leaves smaller polysaccharides (dextrins). Begins in mouth

Question 11

How are dietary disaccharides digested?

Answer 11

Occurs in duodenum and jejunum. Large glycoprotein complexes attached to brush border membrane. Major enzymes - lactase, glycoamylase and sucrase/isomaltase

Question 12

Why is cellulose not digested?

Answer 12

Beta 1,4 glycosidic linkages cannot be broken by any of the enzymes in humans

Question 13

Where is creatine found and what is it’s main function?

Answer 13

In muscles. It’s a small store of energy used for fast release.

Question 14

Give the equation for the formation of ATP and state the energy change

Answer 14

ADP + Pi —> ATP + H2O. 31 kJ/mol

Question 15

Give the equation for the formation of ADP and state the energy change

Answer 15

ATP + H2O —> ADP + Pi. -31kJ/mol

Question 16

Describe the effects of anaerobic respiration

Answer 16

LDH is utilised, leading to a build up of NAD+ and lactate - can lead to lactic acidosis

Question 17

How are levels of lactate in the blood controlled?

Answer 17

Controlled by buffering capacity of the plasma. Renal threshold is >5mM - if this is exceeded the person is lactic acidotic

Question 18

What is lactose intolerance?

Answer 18

Low activity of lactase meaning that lactose cannot be digested.

Question 19

What is galactosaemia?

Answer 19

Inability to utilise galactose due to lack of galactokinase (relatively rare - accumulation of galactose in tissues) or galactose-1-phosphate uridyl transferase (more common - accumulation of galactose and galactose-1-phosphate, toxic to liver, in tissues)

Question 20

What does accumulation of galactose lead to?

Answer 20

It gets reduced to galctitol by aldose reductase.

Question 21

What is the treatment for galactosaemia?

Answer 21

No lactose in diet

Question 22

Write the reaction for galactose to galactitol

Answer 22

Galactose —> galactitiol

NADPH –>NADP+