PHGY 215 – FINAL 2026 ACTUAL EXAM PAPER
QUESTIONS WITH SOLUTIONS GRADED A+
◉ describe the two different types of bands in skeletal muscle
myofibrils.
Answer: A-band (DARK)
-stacked thick and thin filaments
-the area in the A-band where the thick and thin filaments overlap
contains cross-bridges
-lighter portion in the middle = H zone, contains heavy chains
-M line: holds the thick filaments together, runs down the middle of
the H zone
I band (LIGHT)
-thin filaments that do not extend to the A band
-middle portion = Z line
-the distance from one Z line to another is called a sarcomere --> the
functional unit of skeletal muscle
◉ list the properties of thick filaments
(skeletal muscle).
Answer: MYOSIN
,-dimer of two subunits
-a motor protein
-uses ATP to move along actin filaments
-heads that stick out contain an actin binding site & a myosin ATPase
site
◉ list the properties of thin filaments
(skeletal muscle).
Answer: ACTIN
-two actin filaments, each made up of spherical actin molecules
-tropomyosin is a regulatory double helix protein that covers the
active binding sites, preventing the interaction of actin and myosin
-troponin is a regulatory protein made of three polypeptides -
binding to tropomyosin, actin, and Ca2+
◉ describe the sliding filament mechanism in skeletal muscle
contraction.
Answer: -cross bridge formation forms the basis of the sliding
filament mechanism
-thin filaments move inwards over thick filaments, z lines move
closer together
--> all sarcomeres shorten to the same degree
,-neither the length of the thin filaments or thick filaments changes,
just the degree of overlap
-the power stroke is the interaction between myosin and actin that
leads to shortening of the sarcomere
◉ what is the primary storage site for calcium in skeletal muscle
cells?.
Answer: sarcoplasmic reticulum (SR)
◉ describe the steps of the cross-bridge cycle in skeletal muscle.
Answer: 1. binding:
-The ATPase site on myosin head binds ATP, and it splits it into ADP
and inorganic phosphate (Pi)
-Stored energy is released and transferred to the myosin cross-
bridge
2. power stroke:
-In the presence of Ca2+, the troponin-tropomyosin complex
exposes the actin molecules and the cross-bridge can bind with the
actin molecule
-Myosin head bends, pulling thin myofilament inward
, -During the power stroke, the Pi is released and when the power
stroke is complete, the ADP is also released leaving the ATPase site
empty yet the cross-bridge is still bound to the actin
3. detachment:
-Cross-bridge detaches at end of power stroke and returns to
original conformation, caused by binding of a new ATP
--> cycle repeats!
◉ define excitation-contraction coupling in skeletal muscles.
Answer: The process of converting an electrical signal into an actual
contraction
-at the motor end plate, Ach is released into the neuromuscular
junction where it causes permeability changes and initiates an
action potential
-sarcoplasmic reticulum & t-tubules help transmit this signal to the
muscle fibres
◉ describe motor unit recruitment and how it influences muscle
contraction.
Answer: -once a motor neuron enters a muscle, it branches out and
innervates multiple muscle fibres; when that motor neuron is
QUESTIONS WITH SOLUTIONS GRADED A+
◉ describe the two different types of bands in skeletal muscle
myofibrils.
Answer: A-band (DARK)
-stacked thick and thin filaments
-the area in the A-band where the thick and thin filaments overlap
contains cross-bridges
-lighter portion in the middle = H zone, contains heavy chains
-M line: holds the thick filaments together, runs down the middle of
the H zone
I band (LIGHT)
-thin filaments that do not extend to the A band
-middle portion = Z line
-the distance from one Z line to another is called a sarcomere --> the
functional unit of skeletal muscle
◉ list the properties of thick filaments
(skeletal muscle).
Answer: MYOSIN
,-dimer of two subunits
-a motor protein
-uses ATP to move along actin filaments
-heads that stick out contain an actin binding site & a myosin ATPase
site
◉ list the properties of thin filaments
(skeletal muscle).
Answer: ACTIN
-two actin filaments, each made up of spherical actin molecules
-tropomyosin is a regulatory double helix protein that covers the
active binding sites, preventing the interaction of actin and myosin
-troponin is a regulatory protein made of three polypeptides -
binding to tropomyosin, actin, and Ca2+
◉ describe the sliding filament mechanism in skeletal muscle
contraction.
Answer: -cross bridge formation forms the basis of the sliding
filament mechanism
-thin filaments move inwards over thick filaments, z lines move
closer together
--> all sarcomeres shorten to the same degree
,-neither the length of the thin filaments or thick filaments changes,
just the degree of overlap
-the power stroke is the interaction between myosin and actin that
leads to shortening of the sarcomere
◉ what is the primary storage site for calcium in skeletal muscle
cells?.
Answer: sarcoplasmic reticulum (SR)
◉ describe the steps of the cross-bridge cycle in skeletal muscle.
Answer: 1. binding:
-The ATPase site on myosin head binds ATP, and it splits it into ADP
and inorganic phosphate (Pi)
-Stored energy is released and transferred to the myosin cross-
bridge
2. power stroke:
-In the presence of Ca2+, the troponin-tropomyosin complex
exposes the actin molecules and the cross-bridge can bind with the
actin molecule
-Myosin head bends, pulling thin myofilament inward
, -During the power stroke, the Pi is released and when the power
stroke is complete, the ADP is also released leaving the ATPase site
empty yet the cross-bridge is still bound to the actin
3. detachment:
-Cross-bridge detaches at end of power stroke and returns to
original conformation, caused by binding of a new ATP
--> cycle repeats!
◉ define excitation-contraction coupling in skeletal muscles.
Answer: The process of converting an electrical signal into an actual
contraction
-at the motor end plate, Ach is released into the neuromuscular
junction where it causes permeability changes and initiates an
action potential
-sarcoplasmic reticulum & t-tubules help transmit this signal to the
muscle fibres
◉ describe motor unit recruitment and how it influences muscle
contraction.
Answer: -once a motor neuron enters a muscle, it branches out and
innervates multiple muscle fibres; when that motor neuron is
