5.7 - Respiration Flashcards
Why do living organisms need energy?
Active transport; endocytosis, exocytosis incl secretion of large molecules from cell; protein synthesis; DNA replication; cell division; movement of flagella, cillia, motor proteins; activation of molecules eg phosphorylation of glucose in glycolysis.
Define a catabolic reaction.
Metabolic reaction in which large molecules are hydrolysed to small molecules.
Define an anabolic reaction.
Metabolic reaction in which larger molecules are synthesised from smaller molecules.
What is the structure of ATP?
Adenine, ribose, three phosphate groups.
Why is ATP a good energy store?
Universal; stable in solution within cells; energy easily released by hydrolysis; energy released in small, manageable amounts.
What are the two types of respiration and when are they used?
Aerobic respiration – in presence of plenty of oxygen.
Anaerobic respiration – in absence of oxygen.
Name the 4 stages of respiration.
Glycolysis, link reaction, Krebs cycle, electron transport chain.
Describe what happens in glycolysis, where it occurs and what is produced.
Glycolysis happens in the cytoplasm of all living organisms.
It does not require oxygen.
Glucose is phosphorylated by two phosphate molecules to make phosphorylated glucose.
Two phosphate molecules came from the hydrolysis of 2 molecules of ATP into ADP and Pi.
This lowers the activation energy so that the following reactions can occur.
Phosphorylating glucose maintains glucose concentration gradient so diffusion continues.
Phosphorylated glucose is split into 2 molecules of triose phosphate.
Triose phosphate is oxidised, NAD reduced to NADH.
4 ATP are regenerated from ADP and Pi, per triose phosphate.
Triose phosphate is converted to pyruvate.
Net yield is: 2 ATP, 2 NADH, 2 pyruvate.
Describe the structure of a mitochondrion.
Rod shaped, cylindrical.
0.5.-1.0μm.
Length: 2.0-5.0μm.
Inner and outer phospholipid membranes separated by intermembrane space.
Inner membrane folded into cristae, embedded with transport proteins and ATP synthase.
Inner membrane encloses matrix - semi rigid, gel like, contains ribosomes, looped mitochondrial DNA and enzymes.
How do the structures of mitochondria support their function?
Matrix: contains enzymes needed for link reaction and Krebs cycle, contains coenzymes NAD and FAD, contains 4C oxaloacetate needed for Krebs cycle, mitochondrial DNA which codes for some mitochondrial enzymes and proteins, mitochondrial ribosomes for protein synthesis.
Outer membrane: phospholipid bilayer similar to that of other membrane bound organelles, contains carrier and transport proteins.
Inner membrane: phospholipid bilayer differs in composition, impermeable to small ions eg H+, folded to provide large surface area for carrier proteins and ATP synthase - the electron transport chain.
Intermembrane space: space between membranes allows for compartmentalisation of ions and intermediates, enables proton concentration gradients to form for chemiosmosis.
Electron transport chain: series of electron carrier proteins embedded in cristae, known as oxio-reductase enzymes, each protein complex contains a non-protein haen cofactor, three of the four complexes use energy from electrons to pump protons from matrix to intermembrane space, proton gradient forms, protons flow through ATP synthase to synthesis ATP.
ATP synthase: stalked enzyme embedded in cristae, acts as proton channel for proton flow.
Describe what happens in the link reaction, where it occurs and what is produced.
The link reaction only occurs in the presence of oxygen.
The link reaction occurs between the cytoplasm and the mitochondria.
The pyruvate from glycolysis is actively transported into the mitochondria via a pyruvate H+ symport protein
pyruvate is decarboxylated, CO is removed as carbon dioxide.
Pyruvate is dehydrogenated, H is used to reduce NAD the remaining 2C acetyl group combines with coenzyme A to make acetylcoenzyme A.
Acetyl group carried into matrix to be used in Krebs cycle.
What is the coenzyme involved in the link reaction?
Coenzyme A, CoA.
Describe what happens in the Krebs cycle (citrus acid cycle), where it occurs and what is produced.
The Krebs cycle happens in the mitochondrial matrix in a series of enzyme catalysed reactions.
Acetylcoenzyme A is released from the 2C acetate.
CoA is recycled back to cytoplasm.
2C acetate combines with a 4 carbon molecule, oxaloacetate, to make a 6 carbon molecule, citrate.
Citrate is decarboxylated, releasing carbon dioxide, and it is dehydrogenated, hydrogen used to reduce NAD.
5C molecule is decarboxylated and dehydrogenated to produce one molecule of carbon dioxide and one molecule of NADH.
This gives a 4C molecule which briefly combines with CoA leading to the phosphorylation of ADP to give ATP by substrate level phosphorylation. The 4C molecule is dehydrogenated to form FADH2.
The 4C molecule is isomerized and dehydrogenated to regenerate oxaloacetate.
For every glucose molecule there are two turns of the Krebs cycle.
Net yield: Two molecules of carbon dioxide are released; three NADs are reduced to NADH; one FAD is reduced to FADH2; one molecule of ATP is made from ADP and Pi by substrate level phosphorylation.
State the product made per glucose molecule and how much is made in the link reaction and Krebs cycle.
NADH (redNAD): Link reaction: 2 Krebs cycle: 6
FADH (redFAD): Link reaction: 0 Krebs cycle: 2
Carbon dioxide: Link reaction: 2 Krebs cycle: 4
ATP: Link reaction: 0 Kreb cycle: 2
State the other respiratory substrates that can be respired aerobically.
Fatty acids - broken down into acetate, enter Krebs cycle via CoA.
Glycerol - converted into pyruvate, into link reaction then Krebs cycle.
Amino acids - deamination, remaining carbon skeleton enters Krebs or is converted to pyruvate and enters link reaction.
What is chemiosmosis?
Flow of protons, down their concentration gradient, across a membrane, through a proton channel in ATPsynthase.
