Muscle Structure and DMD

The role of dystrophin in muscle cells

.protects the cell from damage during contractions,
.Dystrophin links actin to the extracellular sarcolema

Role of calcium ions in muscle contractions

.Calcium controls muscle contractions
.on actin, the binding sites for mysosin heads are covered by blocking complex (Troponin & tropomyosin)
.Calcium ions bonds to troponin
.moves the tropomyosin away
.calcium exposes the binding sites for the myosin heads.

The role of CK in normal muscle vs DMD

Normal
-CK instantly helps make ATP
-Muscle contractions need a constant ATP supply
-Inside muscle cells
In DMD
- fragile muscle cells tear easily
-CK leaks out into the bloodstream
-High Ck levels in blood
-Muscles loses its energy support

Structure of muscle cells

muscle-->fasical-->muscle fiber-->myofibril-->sarcomere

Structure of Sarcomere

Contains
-Actin (thin fillaments)
- Mysosin (thick filaments)
. Z - lines --> boundries of the sarcomere
. A band --> length of myosin (thick filaments)
. I band --> Actin only (shortens)
. H zone--> mysoin only (shortens)
Key idea: Sarcomeres shorten--> whole muscle contracts

Sliding filaments model (mechanisms of contractions)

Step 1: Nerve impulse & calcium release
-Nerve impulse reaches the muscle fiber
-Triggers release of calcium ions
Step 2: Calcium exposes binding sites
- Calcium binds to troponin, this moves tropomyosin
-Calcium exposes binding sites
Step 3: Step 3: Sliding mechanism (actin + myosin)
- actin slides to myosin
Step 4: Sarcomere shortening
-sarcomere shortens → muscle contracts

Full detail about what happens to muscle cells in DMD

1. No dystrophin--> unstable muscle cell membrane
-caused by mutation
2. Damage during contraction
-The membrane gets tiny tears
3. Calcium floods into the cell
- Tears allow excess calcium to enter the muscle
4. muscle fibers eventually die
5. failed regenaration
-Damage happens faster than rapiers
6. Replacment with fat
- dead muscle fibers are replaced with fat tissue