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PHGY 215 Module 4 Questions and Answers Fully Solved 100%
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What is a regulatory protein complex made of three polypeptides. Where do the three polypeptides bind? - ️️-troponin -one binds to tropomyosin, one binds to actin, one binds to Ca2+ What bands (that are also called dark bands) are made up of stacked thick and thin filaments that are aligned...

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  • November 15, 2024
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  • 2024/2025
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PHGY 215 Module 4
What is a regulatory protein complex made of three polypeptides. Where do the three
polypeptides bind? - ✔️✔️-troponin
-one binds to tropomyosin, one binds to actin, one binds to Ca2+


What bands (that are also called dark bands) are made up of stacked thick and thin
filaments that are aligned parallel to each other. Its borders are defined by the length of
the thick filaments. - ✔️✔️A band

Looking at a cross section of a ___________ you can see a highly organized
cytoskeletal patter of ______ and _____ filaments, which are myosin and actin,
respectively. - ✔️✔️myofibril, thick and thin

Which neurotransmitter innervates the muscle at the neuromuscular junction? -
✔️✔️ACh

A whole skeletal muscle is made up of individual _________ _________, each of which
runs the entire length of the muscle. - ✔️✔️muscle fibres

Muscles fibres run parallel to each other and are surrounded by what? -
✔️✔️connective tissue

TRUE OR FALSE: a muscle fibre is actually a single muscle cell - ✔️✔️True

TRUE OR FALSE: muscle cells are multinucleated and have a very large number of
mitochrondria. - ✔️✔️True

Along the length of a muscle fibre, the cell is divided into discrete contractile elements
called...? - ✔️✔️myofibrils


The middle of the A band is slightly lighter because the thin filaments do not reach this
far from the ends. What is this lighter portion also called? - ✔️✔️H zone

What bands (also called light bands) are made up of the portion of thin filaments that do
not extend into the A band? - ✔️✔️I band

What is found in the middle of the I band? - ✔️✔️a vertical line called the Z line

,Myosin is composed of 2 heavy chains and 2 light chains. The H zone only contains the
_______ chains. - ✔️✔️heavy

What does the H zone contain? - ✔️✔️the M line that contains proteins that hold thick
filaments (myosin) in a stack

The proteins that hold the thick filaments together in a stack are seen as the ____ line. -
✔️✔️M line

The ____ line runs down the centre of the H zone. - ✔️✔️M line

The distance from one ____ line to the next is called a sarcomere. - ✔️✔️Z line

What is considered the functional unit of skeletal muscle? - ✔️✔️a sarcomere

When muscles are growing, they extend the length of the muscle fibre by adding new
______________ onto the ends. - ✔️✔️sarcomeres

When relaxed, a sarcomere is about how many micrometres? - ✔️✔️2.5

The area in the A band where the thick and thin filaments overlap contains
________________, that extend from the thick filaments and form when thin filaments
bind. - ✔️✔️cross-bridges

Myosin is a _________ protein, in that it uses ATP to move along actin filaments. -
✔️✔️motor

TRUE OR FALSE: each molecule of myosin is a dimer of two subunits. - ✔️✔️True

TRUE OR FALSE: each subunit of actin looks like a golf club, in that it has a long shaft
with a globular head. - ✔️✔️False, each subunit of MYOSIN looks like a golf club.


What 3 things make up the thin filament? - ✔️✔️actin, tropomyosin, and toponin

Actin filaments are made up of individual spherical actin molecules that come together
to form a ________ __________ structure. - ✔️✔️double helix

What is a regulatory protein that covers the active binding sites, preventing the
interaction of actin and myosin? - ✔️✔️Tropomyosin

What is a thin, double helix protein that lies end to end along the actin helix structure? -
✔️✔️Tropomyosin

, Cross-bridge formation forms the basis of the sliding filament mechanism which brings
about...? - ✔️✔️muscular contraction

Sarcomere goes from z-line to z-line & has __________ in the middle with ________ on
the sides. - ✔️✔️myosin, actin

During contraction, the thin filaments move inwards over the thick filaments. When this
happens, the _________ move closer together. This occurs simultaneously along the
fibre & all _____________ shorten to the same degree. - ✔️✔️z-lines, sarcomeres

What is a concentric contraction? - ✔️✔️the whole muscle shortens

What does the power stroke refer to? - ✔️✔️the interaction btwn myosin & actin that
leads to a shortening of the sarcomere

What are the four steps of the power stroke? - ✔️✔️Binding
-myosin cross-bridge binds to actin molecule

Power stroke
-the myosin head bends, pulling thin myofilament inward

Detachment
-cross-bridge detaches at end of power stroke & returns to original conformation

Binding
-cross-bridge binds to more distal actin molecule; cycle repeats

What is the result of a power stroke? - ✔️✔️the actin molecules being pulled closer to
the centre of myosin molecules

TRUE OR FALSE: on each successive cross-bridge cycle, the actin is pulled even
more. - ✔️✔️True

TRUE OR FALSE: at any given time, all cross-bridges are actively pulling actin. -
✔️✔️False, not all cross-bridges are actively pulling actin; some are just holding the
actin in position while others prepare for the next power stroke.

TRUE OR FALSE: each myosin has two heads, which act independently in that only
one of them may be attached to actin at any given time. - ✔️✔️True

TRUE OR FALSE: power strokes are directed away from the centre of the myosin
molecule. - ✔️✔️False

TRUE OR FALSE: each myosin molecule is surrounded by six actin molecules -
✔️✔️True

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