Myofibrils

Question 1

Where are myofibrils located?

Answer 1

• each muscle fibre contains many myofibrils

Question 2

WHat are myofibrils?

Answer 2

• these are long cylindrical organelles made of protein and specialised for contraction

Question 3

Why do fibres contain many myofibrils?

Answer 3

• they provide almost no force own their own
• collectively they are very powerful

Question 4

How are myofibrils made more powerful?

Answer 4

• they are lined up in parallel to provide maximum force when they contract all together

Question 5

What are the two types of protein filament that make up myofibrils?

Answer 5

• actin
  
  • the thinner filament
  • consists of two strands twisted around each other
• myosin
  
  • the thicker filament
  • consists of long rod-shaped fibres with bulbous heads that project to one side

Question 6

Why does myofibrils have astribed appearance?

Answer 6

they have alternating light and dark bands

Question 7

What are the light bands?

Answer 7

• these appear light as they are a region where the actin and myosin filament do no t overlap
• they are also known as isotopic bands or I-bands

Question 8

What are the dark bands?

Answer 8

• these appear dark because of the presence of thick myosin filaments
• the edges are particularly dark as the myosin is overlapped with actin
• they are also known as anisotropic bands or A-bands

Question 9

WHat are Z-lines?

Answer 9

• this is a line found at the centre of each light band
• these distance between adjacent lines is called a sacromere

Question 10

What is a sacromere?

Answer 10

• the sacromere is the functional unit of the myofibril
• when a muscle contract the sacromere shortens

Question 11

What is the H-zone?

Answer 11

• this is a lighter coloured region found in the centre of each dark band
• only myosin filaments are present at this point
• when the muscle contractst the H-zone decreases