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Flashcards in Biochemistry Deck (136)
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How do catalysts function?

They speed up reaction rate by lowering activation energy


What is the transition state (intermediate) in a reaction?

This is the unstable stage beween reactants and products


What is glycogen storage disease and what are its consequences?

It is an enzyme deficiency that results in the failure of glycogen to reach the phosphorylated transition state

This means glucose cannot be obtained from glycogen stores

Hepatomegaly (fatty liver) will result due to glycogen build up


What are the variants of the extra molecules (as well as enzymes) that are often reqired for some enzymatic processes to proceed?

  • Cofactors - metal ions
  • Coenzymes - organic molecules


What are metal ions that contain metal cofactors called?



Like enzymes, cofactors are always ____________ at the end of a reaction



Tightly bound coenzymes are called what?

Prosthetic groups

(these confer additional function)


What is the term given to an enzyme without a cofactor?



An enzyme with a cofactor is called what?



Give examples of metal ions that could be used as cofactors

  • Zinc
  • Copper
  • Iron


Give examples of coenzymes

  • Vitamins
  • NAD
  • FAD
  • Lipoate


Binding of a substrate to an ezyme results in what?

Conformational change of the enzyme around the substate

This is induced fit (due to intermolecular bonding)

The enzyme/substate complex is now formed


Which two main factors affect enzyme fucntionality?

  1. Temperature
  2. pH


Describe the how temperature can affect the rate of an enzymatic reaction

It will increase to a point and then sharply drop off (past the optimum temp) due to enzyme denaturing


Describe how increasing pH affect the rate of an enzymatic reaction

It will increase as pH increases until the optimum rate is achieved (at optimum pH) and then will decrease again

This produces a bell curve



What are isozymes?

Enzymes which have almost identical function but have slightly different amino acid sequencing


How can the number of certain isozymes in certain tissues/blood be used to diagnose a medical condition?

Different isozymes are synthesised in different regions of the body or at different atges in embryonic/foetal development

Finding the "wrong" isozyme at a certain time, or location in the body may be indicative of a medical condition


How can phosphorylation regulate enzyme activity?

It can convert the enzyme between inactive and active forms


Phosphorylation is a reversible process that involves which two enzymes?

  1. Kinase - adds phosphate
  2. Phosphotase - removes phosphate


What are zymogens?

Inactive precursors of an enzyme which are converted to active forms by cleavage of a covalent bond


What is produced after the catabolism of glucose?

Two pyruvate molecules

There is also a net gain of 2ATP, 2NADH and 2H+


What is NAD+?

Nicotinamide adenine dinucleotide

It is derived from niacin - a vitamin

It is used as an electron carrier by forming NADH


What is NADH required for?

The transfer of electrons to the respiratory electron transfer chain in stage 3 of ATP synthesis


What are the three diferent terms used to describe the second stage of ATP synthesis?

  1. Citric acid cycle
  2. Krebs cycle
  3. Tricarboxylic acid cycle (TCA)


Where does the TCA cycle occur?

Mitochondrial matrix on the inner membrane

(this is where proteins required for the electron transport chain can be found, as well as ATP synthase and transport proteins)


Where is pyruvate synthesised?

The cytosol


How does pyruvate enter the matrix of the mitochondria? (3)

It must cross two membranes

  • The intermembrane space is very acidic creating a pH gradient from the cytosol to the matrix which pyruvate can follow
  • There is also a electrochemical gradient and pyruvate can utilise this as it is attracted to H+
  • A pyruvate symport transporter allows entry of pyruvate into the mitochondria using H+/pyruvate symport, a form of contransport, by faciliated diffusion


Which process must pyruvate undergo to be converted to acetyl-CoA?

Oxidative decarboxylation

This is an irreversible reaction


Describe the four stages of the oxidative decarboxylation of pyruvate

  1. Pyruvate dehydrogenase converts pyruvate to hydroxyethyl thiamine pyrophosphate (HETPP), CO2 is given off as a by product
  2. Dihydrolipoyl transacetylase transfers (and oxidises) the hydroxyethyl group to lipoic acid which forms acetyl dihydrolipoamide
  3. The acetyl group is transferred to CoA forming one acetyl CoA per pyruvate
  4. NAD+ reoxidises dihydrolipoamide which forms one NADH - this is mediated by dihydrolipoyl dehydrogenase


Describe the TCA cycle

  1. Acetyl CoA forms citric acid upon binding to a four carbon subunit
  2. Decarboxylation of citric acid occurs twice yielding 2CO2
  3. Citric acid will also go through four oxidation reactions yielding 3NADH, 3H and FADH2
  4. As a result GTP is produced, and by the end the 4-carbon subunit is reformed