1. Revision You asked to look at sliding filament theory…
I feel we need to quickly start with muscle structure.

2. Voluntary /striated /skeletal muscle!
Muscles are made up of bundles of muscle fibres
Each fibre is a single muscle cell and can be several cms in length. (0.1mm in diameter)
Bound together by connective tissue continuous with tendons.
With a cell surface membrane: called sarcolemma
Each cell is multinucleate: a single nucleus could not effectively control metabolism of such a long cell! Would take too long to move proteins.
Striped: ability to contract
Voluntary /striated /skeletal muscle!

3. One nuclei would be ineffective at controlling the cells metabolic process over such a long cell – e.g. if only one nuclei any enzymes needed for reactions produced in protein synthesis – would struggle to diffuse throughout the entire length of the cell
Enzymes needed here also and in large quantities – but the further the distance the less reliable diffusion – the solution is to have more than one nuclei

4. Longitudinal Microscope picture of skeletal muscle

5. Muscle....
The muscle fibre contains sarcoplasm (cytoplasm) with numerous mitochondria
Protein molecule: myoglobin
Each muscle fibre is a bundle of smaller myofibrils arranged lengthways
Each myofibril is made up of 2 kinds of protein myofilaments: actin (thin) and myosin (thick)
These make up the contractile units called sarcomeres

6. Synoptic: Other pigments
Myoglobin:
Red pigment found in muscle cells.
It doesn’t carry oxygen but it stores oxygen.
It has got just one polypeptide chain, hence its dissociation curve’s shape.
Has a greater affinity for oxygen

8. Are there any other key words you could include?
Task
In pairs: Put the words given to you in order to explain the structure of a voluntary muscle
Are there any other key words you could include?

9. Muscle, made up of…
Bundle of muscle fibres
Muscle fibre is the cell
Each muscle fibre is surrounded by the Sarcolemma
Each muscle fibre is a bundle of Myofibrils (organelles)
Myofibrils are made up of Myofilaments
Actin
Myosin
Sarcomere
The sarcomere is the smallest contractile unit of a muscle……………

10. The sarcomeres span from one Z line to the next.

11. Write bullet points to summarise your understanding at
Watch animation
Write bullet points to summarise your understanding at
THIS STAGE

12. Muscle contraction:
The contractile unit : the sarcomere is made up of 2 types of protein molecule:
Actin: thin
Myosin: Thick
Contraction is bought about by the coordinated sliding of these proteins filaments within the sarcomere
The proteins overlap=striated appearance.
Actin only=light
Actin+myosin=dark
Myosin only =medium

13. The sarcomeres span from one Z line to the next.
The Z lines are drawn closer in contraction as I band and H zone are reduced. A band does not change

14. (a) Diagram showing a section of myofibril to reveal sarcomere layout;
(b) diagram showing the bands and zones present.
(a)

16. DRAW THE BANDING PATTERN!
Actin and myosin filaments in one sarcomere relaxed
Z line
The banding pattern of above
The arrangement of the sarcomere when contracted
DRAW THE BANDING PATTERN!

17. The central band of myosin alone has disappeared
Either just actin or actin+myosin

18. The banded pattern shown in micrographs is due to the overlapping regions of the two types of fibre18

19. In 1mm fibre=400 sarcomeres!
Human thigh muscle= sarcomeres!

20. How the Sarcomere Shortens
First watch this animation
Bullet point your understanding

21. Actin
Actin molecules are 2 strands made mainly of the protein actin (F actin) which are coiled around each other (twisted beads!)
Associated with 2 other protein molecules:
Tropomyosin: rod shaped protein that coils around the F actin, reinforcing it
Troponin: these complexes made of 3 polypeptides are attached to each tropomyosin molecule ,one polypeptide binds to tropomyosin, one to the actin and one to calcium ions

22. Myosin: Myosin are the thick protein filaments
Each myosin molecule consists of a tail and 2 protruding heads
Myosin molecule heads protrude from the fibre
When a muscle contracts it is the orientation of these that brings about the movement of actin
Myosin heads attach to actin, dip forward and slide the actin over the myosin
This is the sliding filament theory.

23. Myosin heads cannot bind to actin filaments
troponin
tropomyosin
actin filament
ADP
myosin complex Pi
myosin filament
At rest, the actin-myosin binding site is blocked by tropomyosin, held in place by troponin
Myosin heads cannot bind to actin filaments

24. A nerve impulse arrives at the neuromuscular junction
Calcium ions are released from the sarcoplasm reticulum (specialised ER)
Diffuse through the sarcoplasm
Bind to troponin molecule
Initiates the moving of the myofilaments: actin and myosin.

25. Ca2+ binds to troponin, changing its shape
Tropomyosin is pulled out of the binding site: shifts position and exposes myosin binding site
Myosin head can bind – bond is actin-myosin cross bridge

26. When myosin binds to actin stimulates ATPase, breaking down ATP to ADP + Pi
Energy provided changes myosin head to nod forward, pulling actin filament along in a ratchet motion over myosin
This is the power stroke, ATP is used

27. Free ATP binds to myosin head
Actin-myosin cross bridge breaks: myosin head detaches
ATP is hydrolysed, and myosin head returns to original upright shape

28. With continued stimulation the cycle is repeated
The collective bending of many myosin heads combines to move the actin filaments relative to the myosin= muscle contraction

29. If stimulation ceases, Ca2+ is actively pumped back into sarcoplasmic reticulum (needs ATP)
Troponin and tropomyosin return to original positions
Muscle fibre is relaxed

30. Task: 10 minutes
Watch
Then use your understanding to put the statements in order to describe the steps that must occur to bring about contraction of a sarcomere

31. Write bullet points to summarise your understanding at
Watch animation again?
Write bullet points to summarise your understanding at
THIS STAGE

32. Please get out your 4 questions for homework to hand in
Starter: 10 minutes
Please get out your 4 questions for homework to hand in
Watch: Fantastic 4 minutes
Get out your sheet you were completing on sliding filament theory and mark
I am going to give you some questions/mark schemes I had copied that we had not used, they are for your own practice
We will complete the last bit on muscles……

33. Learning outcomes:
Explain, with diagrams and photographs how muscles contract in terms of the sliding filament theory.
Outline the role of ATP in muscular contraction and how the supply of ATP is maintained in muscles

34. Homework 1
Collate diagrams and photographs to explain the sliding filament theory.
Annotate these diagrams to show your understanding. Include voluntary muscle structure, sarcomere etc.
Extension: 2 good biological sciences review articles on muscle on my website.

35. The role of ATP
List the stages where ATP is involved in muscle contraction 3 marks
In the power stroke: when the myosin head attaches to actin binding site and bends energy is required
Energy is required to break this cross bridge and for the myosin head to go back to its original position
When contraction finishes to pump calcium ions back into sarcoplasmic reticulum

36. Maintenance of the ATP supply
There is only enough ATP to provide 1-2 seconds worth of contraction
So ATP must be regenerated as quickly as it is used
There are 3 mechanisms for this:

37. Three energy systems summary:
Cells cannot store much ATP At start of exercise immediate recharge of ATP is made using creatine phosphate Stored in muscle cell sarcoplasm and can be hydrolysed to release energy Energy is used to regenerate ATP from ADP and Pi. Creatine phosphate provides the Pi Creatine phosphate creatine + Pi ADP + Pi ATP Creatine phosphate + ADP creatine + ATP No oxygen needed Provide energy for 6-10 seconds Known as the ATP/CP system

38. During exercise Energy first supplied by ATP/PC system
Anaerobic respiration: in muscle cell sarcoplasm. Quick but produces lactate which is toxic. Lactate enters blood where it leads to stimulation of more blood to the muscles
Aerobic respiration in muscle cell mitochondria can regenerate ATP as quickly as it is broken down if there is sufficient supply of oxygen and respiratory substrate to the muscles
Allows exercise to be sustained.

39. Suggest which process for ATP regeneration is most important for
Quick question
Suggest which process for ATP regeneration is most important for
A marathon runner
100m sprinter?

40. Plenary exam question 8 marks = 8 minutes
Independently complete the examination question….. WWW/EBI? Extension: Question 2 9 marks

41. Test Biotechnology Please reflect on your test result
One person got their TG
Most others were the grade below, so generally good
Lack of revision/understanding evident in some areas??
Exam technique: read the questions more carefully…
Your Mock??