Cellular Energy, ATP, Digestion, and Muscle Physiology: Part A–B

Energy

The ability to do work or cause change.

Chemical energy

Energy stored in chemical bonds, including bonds in nutrients.

Work

The ability to move something; cellular work requires energy in the form of ATP.

Kinetic energy

Energy of motion.

Potential energy

Stored energy.

ATP

Adenosine triphosphate; the form of energy cells can use to power cellular work.

Structure of ATP

ATP consists of adenine, ribose, and three phosphate groups.

ATP hydrolysis equation

ATP + H₂O → ADP + Pi + energy; removal of the terminal phosphate releases usable energy.

ATP synthesis equation

ADP + Pi + energy → ATP.

Phosphorylation

The addition of a phosphate group to a molecule.

Significance of phosphorylation

Adding a phosphate group can change a molecule's shape or activity and can transfer energy to it.

Why must food energy be converted?

Chemical energy in dietary nutrients is not in the correct form for cells to use directly; it must be converted into ATP.

Why do muscle cells need ATP?

Muscle cells use ATP to provide energy for their work, including contraction.

Dietary nutrient example used in lecture

A hamburger containing a beef patty and a bun is used to illustrate digestion and nutrient delivery.

What happens during digestion?

Large nutrient polymers are broken into smaller monomers in the stomach and small intestine.

Polymers in the hamburger example

The beef patty contains proteins and triglycerides; the bun contains starch.

Protein digestion product

Proteins are broken down into amino acids.

Starch digestion product

Starch is broken down into glucose.

Triglyceride digestion products

Triglycerides are broken down into glycerol and fatty acids.

Where are nutrient monomers absorbed?

In the small intestine, monomers are absorbed by the simple columnar epithelial tissue lining the intestine.

Where do absorbed monomers go first?

They enter blood capillaries in the connective tissue below the simple columnar epithelium.

How do monomers reach body cells?

The circulatory system delivers the monomers to cells throughout the body.

Two possible fates of monomers inside cells

They can be used to build new structures or be used to make ATP.

Glucose used to build structures

Glucose can be used to make glycogen or other carbohydrates.

Amino acids used to build structures

Amino acids can be used to make new proteins.

Fatty acids used to build structures

Fatty acids can be used to make new lipids.

Cellular respiration

The chemical breakdown of glucose to form ATP; other organic molecules can also be used to make ATP.

Cellular respiration equation shown in Part A

C₆H₁₂O₆ + 6 O₂ → 12 H₂O + 6 CO₂ + 36 ATP + heat. This is the simplified equation as shown in the lecture.

Three reactions of aerobic cellular respiration listed in Part A

Glycolysis, Krebs cycle, and electron transport chain.

Aerobic

A reaction or process that requires oxygen (O₂).

Aerobic cellular respiration

ATP production using oxygen; the lecture's overall cellular respiration equation represents aerobic cellular respiration.

Anaerobic cellular respiration (lecture usage)

ATP production without oxygen; the lecture describes it as using glycolysis only, not the Krebs cycle or electron transport chain.

Glycolysis equation shown in Part A

Glucose → pyruvic acid + 2 ATP. The lecture notes this is a simplified version, not the complete glycolysis reaction.

How much ATP does glycolysis make in the Part A lecture?

2 ATP, a small amount compared with the lecture's 36 ATP total for aerobic cellular respiration.

Does glycolysis require oxygen?

No. Oxygen is not required for glycolysis.

What happens to pyruvic acid during anaerobic ATP production in muscle?

It is converted to lactic acid inside the cell, according to the lecture.

Lactic acid buildup in the Part A lecture

The lecture states that too much lactic acid accumulating inside a cell can lead to muscle cramps.

What happens to lactic acid after it forms?

It eventually diffuses out of the cell into the blood, where other cells can use it to make ATP, according to the lecture.

Functions of the muscular system

Movement of the whole body and substances through the body; stabilization of posture; heat production; and control of body openings and passages.

Sphincter muscles

Muscles that form rings around body openings; some prevent material from passing through when they contract.

Number of named muscles in the human body (lecture figure)

697.

Muscle tissue: responsiveness (excitability)

The ability to respond to a stimulus. In the lecture, the stimulus is a neurotransmitter binding to its receptor on the muscle-cell membrane.

Stimulus

An environmental change.

Action potential (Part B introduction)

A change in the distribution of sodium (Na⁺) and potassium (K⁺) inside and outside the cell, caused by the stimulus-response process described in the lecture.

Muscle tissue: contractility

The ability to contract, or shorten; the opposite of contraction is relaxation.

Extensibility

The ability to stretch without damage.

Elasticity

The ability to return to original shape and length.

Muscle organ

Each named muscle is a separate organ.

Three connective tissue layers around skeletal muscle

Epimysium, perimysium, and endomysium.

Epimysium

The superficial layer of dense irregular connective tissue surrounding the entire muscle organ.

Perimysium

The middle layer of dense irregular connective tissue surrounding groups of muscle cells (muscle fibers); it forms the fascicles.

Endomysium

The deepest layer; areolar connective tissue surrounding individual muscle fibers within a fascicle.

Fascicle

A bundle or group of skeletal muscle cells (muscle fibers) surrounded by perimysium.

Fusiform fascicle orientation

Thick in the middle and tapered at the ends; examples given are biceps brachii and gastrocnemius.

Parallel fascicle orientation

Fascicles are arranged parallel and the muscle has a uniform width; these muscles are usually very long and can shorten more than other arrangements, but are not as strong because they have fewer cells per fascicle. Example: rectus abdominis.

Triangular (convergent) fascicle orientation

Fan-shaped arrangement; example: pectoralis major.

Pennate fascicle orientation

Feather-shaped arrangement; has many cells and is described in the lecture as the strongest arrangement. Examples: rectus femoris and deltoid.

Circular fascicle orientation

Fascicles form rings around body openings; these muscles are often called sphincters. Example: orbicularis oculi.

Ways muscles can attach

Muscles can attach to connective tissue membranes, other muscles, or bones.

Direct muscle attachment to bone

The epimysium is fused to the periosteum of the bone.

Periosteum

Connective tissue membrane covering the external surface of bone, except at articular surfaces.

Indirect muscle attachment to bone

The epimysium extends beyond the muscle as an aponeurosis or tendon.

Aponeurosis

A sheet of dense irregular connective tissue that extends beyond a muscle to attach it to another structure.

Tendon

A cord of dense regular connective tissue that extends beyond a muscle and attaches it to another structure, often a bone.

Sarcolemma

The muscle cell's cell membrane.

Sarcoplasm

The cytoplasm of a muscle cell.

Multinucleate skeletal muscle cells

Skeletal muscle cells contain multiple nuclei; during embryonic development, each cell forms by fusion of individual cells called myoblasts.

Myoblast

An individual embryonic cell that fuses with other myoblasts to form a skeletal muscle cell.

Striated skeletal muscle cells

Skeletal muscle cells have alternating light and dark bands.

Glycosome

A vesicle in a skeletal muscle fiber that stores glycogen.

Glycogen

A polymer of glucose used by animal cells to store glucose for short-term energy.

Why do skeletal muscle fibers store glycogen?

Muscle cells need a lot of energy; stored glycogen supplies glucose that can be used to make ATP. This is an example of complementarity of structure and function.

Myoglobin

A red, oxygen-storing protein in muscle cells.

Why do muscle cells contain myoglobin?

Muscle cells need substantial energy, and oxygen is required for aerobic ATP production; myoglobin stores oxygen. This is an example of complementarity of structure and function.

Complementarity of structure and function

The idea that a structure's features are suited to its function.

Myofibrils

Thread-like structures running parallel through a skeletal muscle cell; they are the contractile elements that actually shorten during muscle contraction.

Why are myofibrils important?

Because muscle cells contract by shortening, myofibrils provide structures that can shorten; this illustrates complementarity of structure and function.

T-tubules (transverse tubules)

In-pocket extensions of the sarcolemma that reach toward the center of the cell and distribute the action potential to all myofibrils.

Function of T-tubules

They form a communication system that carries the stimulus/action potential into the cell so all myofibrils receive it.

Sarcoplasmic reticulum (SR)

A modified smooth endoplasmic reticulum that surrounds myofibrils and stores and releases calcium.

Striated myofibrils

Myofibrils have alternating dark and light bands.

A band

The dark band of a myofibril; corresponds to the length of the thick myosin filaments.

H zone

The lighter region in the center of the A band; visible when the muscle is relaxed.

M line

The center of the H zone.

I band

The light band of a myofibril.

Z disc

Located at the center of the I-band region; defines the boundary of a sarcomere and anchors thin actin filaments.

Sarcomere — anatomical definition

The region of a myofibril between two Z discs.

Sarcomere — functional definition

The functional unit of a muscle cell; the unit that allows contraction to occur.

Myofilaments

Filaments that make up myofibrils. The lecture identifies thick filaments made of myosin, thin filaments made of actin, and elastic filaments.

Thick filament

Made of myosin; the lecture states that about 200 myosin molecules make one thick filament.

Thin filament

Made of actin and anchored in the Z disc.

Elastic filament

The third type of myofilament identified in the lecture; illustrated in green in the slide figure.

Myosin tail

The tail points toward the M line and forms the shaft of the thick filament.

Myosin head

Extends from the myosin shaft, points toward the thin filament, and can bind actin.

Myosin function

Myosin is a contractile motor protein that binds actin.

Motor protein

A protein that can do work.

Where does myosin get energy to perform work?

From phosphorylation by ATP; the Part B lecture says this process is discussed in more detail in Part C.

Actin structure

Actin is made of oval subunits; the figure labels these as G-actin.

Actin function

Actin is a contractile protein with a myosin-binding site.

Regulatory proteins associated with actin

Troponin and tropomyosin.