Transcript Document 251333

Energy Systems in Muscle
Cells
Higher Human Biology
Unit 1 – Section 8
Learning Intentions
By the end of this section you should be able to:
I can explain how creatine phosphate can break down, releasing phosphate and
allowing the production of ATP from ADP and phosphate during strenuous activity.
I can describe the conversion of pyruvate to lactic acid during strenuous activity
when insufficient oxygen is available, and the build-up of an oxygen debt, which
must be repaid when the activity is over.
I can identify the two types of muscle fibre, and the differences in their number of
mitochondria, blood supply, storage fuel and rate of contraction and give examples of
the type of activities which depend on them.
Creatine Phosphate System
• During intense muscular activity, muscle
cells use ATP as a source of energy.
• However, each muscle cell only contains
enough ATP for a few contractions.
• Most of the energy needed for
repetitive muscular contraction comes
from a chemical called creatine
phosphate.
During Strenuous Activity
Creatine Phosphate
ATP
Phosphate
Creatine
ADP
The breakdown of the creatine phosphate releases the phosphate
which can then convert ADP into ATP by phosphorylation.
This ATP can then be used for muscular contraction for About ten
seconds
Sufficient energy is generated for short bursts of exercise e.g.
100m sprint
During Rest Period
ADP
Creatine
Phosphate
Creatine Phosphate
ATP
When the demand for energy is low during rest, little ATP is
required.
Therefore any ATP is broken down to release energy and phosphate
to regenerate creatine phosphate (acts as a high energy
reserve). This is an enzyme controlled pathway.
Lactic Acid Metabolism
• During strenuous activity, ATP only lasts
seconds. ATP can be replenished by the
breakdown of creatine phosphate until it is
used up.
• Cells will then start to respire anaerobically
(by fermentation) as the cells will not be
receiving an adequate supply of oxygen
• Oxygen is needed for the citric cycle and the
electron transport chain. Without the oxygen
these stages do not occur
Lactic Acid Metabolism
• Only glycolysis produces ATP
(2 instead of 38)
• The pyruvate is converted
into lactic acid (lactate)
• Lactic acid can build up and
cause fatigue and an oxygen
debt builds up
• This process is reversible
when at rest and more oxygen
becomes available.
• The lactic acid is transported
to the liver to be converted
back to pyruvic acid.
Skeletal Muscle Fibres
• Physical activity requires parts of the body to
move and is brought about by skeletal muscle
fibres (either slow-twitch or fast-twitch).
• Skeletal muscles contain a genetically
determined mixture of slow-twitch and fasttwitch fibres. In most muscles the ratio is
balanced.
• However in other muscles one will dominate
For example the back contains mainly slow-twitch
muscles and the eyes mainly fast-twitch
muscles
Myoglobin
• Muscles cells contain an oxygen storing
protein called MYOGLOBIN.
• It has a higher affinity for oxygen than
haemoglobin so can extract oxygen from
the blood to be used by the muscle
cells(especially those in slow twitch
Slow-twitch fibres rely on aerobic respiration Fast-twitch muscle fibres depend on
to generate most of the ATP and are effective glycolysis to generate ATP for power
during endurance exercise such as rowing and events such as sprinting
cycling.