What makes up myosin?

[m25]

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What makes up myosin? Like what are it's subunits?

I've also heard that actin is microfilament, but I thought actin polymer is what makes a microfilament so referring to actin as microfilament does not seem right to me. Can anyone clear this up?

 

[kraskadva]

What makes up myosin? Like what are it's subunits?

Multiple proteins which a) you don't need to know for the MCAT and b) you can find on google.

I've also heard that actin is microfilament, but I thought actin polymer is what makes a microfilament so referring to actin as microfilament does not seem right to me. Can anyone clear this up?

Globular actin (G-actin) is the monomer, Filamentous Actin (F-actin) is the polymer. G-Actin would not be referred to as a microfilament, but F-Actin would be.
Generally in a cell when you're talking about actin, you're only talking about F-Actin microfilaments and these are interchangeably described as "actin microfilaments" or just "actin". If someone were referring to G-actin, that would be specified as G-actin or "free actin"

 

[m25]

Multiple proteins which a) you don't need to know for the MCAT and b) you can find on google.

Globular actin (G-actin) is the monomer, Filamentous Actin (F-actin) is the polymer. G-Actin would not be referred to as a microfilament, but F-Actin would be.
Generally in a cell when you're talking about actin, you're only talking about F-Actin microfilaments and these are interchangeably described as "actin microfilaments" or just "actin". If someone were referring to G-actin, that would be specified as G-actin or "free actin"

Ah, I see. Is F-Actin/actin microfilaments/actin also often referred to as thin filament? Like I keep hearing how in muscles, actin makes up the thin filament, so is the actin used in muscle a polymer of actin or just single units of actin?

 

[kraskadva]

Ah, I see. Is F-Actin/actin microfilaments/actin also often referred to as thin filament? Like I keep hearing how in muscles, actin makes up the thin filament, so is the actin used in muscle a polymer of actin or just single units of actin?

In the sarcomere, actin filaments are the thin filaments. So yes, the polymer.
G-actin doesn't do anything biologically relevant except come together to make F-actin.
So anytime you hear someone talking about actin doing something, or actin filaments in any context, then they are referring to F-actin filaments.

 

[m25]

In the sarcomere, actin filaments are the thin filaments. So yes, the polymer.
G-actin doesn't do anything biologically relevant except come together to make F-actin.
So anytime you hear someone talking about actin doing something, or actin filaments in any context, then they are referring to F-actin filaments.

Thank you, that makes so much sense! So one more question, when myosin is referred to as the thick filament, it means that it's actually the myosin polymer making up the thick filament right?

 

[kraskadva]

Thank you, that makes so much sense! So one more question, when myosin is referred to as the thick filament, it means that it's actually the myosin polymer making up the thick filament right?

yes