A&P - Week 3: Metabolism, Plasma Membrane

What is metabolism?

The sum of all biochemical reactions inside a living cell, involving nutrients

What do anabolic reactions do?

Make things.
They transfer energy from ATP to complex molecules

What do catabolic reactions do?

Break things down.
They transfer energy from complex molecules to ATP

Anabolism + catabolism =

Metabolism

How do nutrients absorbed in the GI tract reach individual cells?

Via the blood

Within cells, nutrients can either be used in anabolic pathways to (a)
or broken down through catabolic pathways to (b)

(a) build complex molecules
(b) form pyruvic acid and acetyl Coenzyme A (CoA)

Where does the final stage of nutrient processing occur?
What is the nature of these reactions?

In the mitochondria.
These reactions are almost entirely catabolic

What occurs in the final stage of nutrient processing?
What are the byproducts, and how do they exit the body?

Oxygen is used to break down food into carbon dioxide and water, producing ATP.
These byproducts (CO2 and H2O) are exhaled.

What is the optimized fuel in the human body?

Glucose

Oxidation-reduction reactions
Oxidization vs. reduction?

Involve the gain of oxygen or loss of hydrogen atoms (and their electrons).
Oxidized substances: lose electrons and energy.
Reduced substances: gain electrons and energy.

Glucose is an energy-rich, highly reduced molecule. What does this mean?
How could it release energy?

Glucose has many hydrogen atoms.
It could release energy by highly oxidizing it with many oxygen atoms or double-bonds.

What happens to:
- C6H12O6
- O2
- Released energy
when we metabolize glucose with oxygen?

- C6H12O6 (glucose) is oxidized to CO2 (carbon dioxide)
- O2 (oxygen) is reduced to water (H2O)
- Released energy is used to make ATP

What are the conditions of chemical reactions in the body?

They occur under very controlled conditions, preferably one reaction at a time. This is so that there isn't too much energy at once, potentially causing a hazard such as too much heat.

What coenzymes are usually needed in redox reactions? What is the role of this coenzyme?

B vitamin coenzyme.
Catalyzes redox reactions

What are 2 important coenzymes that act as hydrogen (or electron) acceptors in an oxidative pathway
What do they derive from?
What can they be reduced to?

- NAD+ derived from niacin (vitamin B3). Can be reduced to NADH + H+
- FAD is derived from riboflavin (vitamin B2). Can be reduced into FADH2

3 important steps of ATP usage

- Briefly holds chemical energy
- Transfers chemical energy into an enzyme to power a chemical reaction (ATP turns into ADP)
- ADP gets recharged into ATP by the mitochondria in order to be used for a new chemical reaction

What are the 2 mechanisms used to make ATP from energy used in cellular respiration?

- Substrate-level phosphorylation
- Oxidative phosphorylation

Substrate-level phosphorylation

Does not require oxygen.
Chemical bonds are broken and energy from reactants is used to phosphorylate ADP into ATP.
When done with glucose, this is glycolysis.
Does not produce much ATP, mainly for quick energy such as a 1 minute sprint.

Oxidative phosphorylation

Requires oxygen.
Energy from food creates a proton gradient (electron transport chain) that's used to attach phosphates to ADP.
Produces much more ATP than substrate-level phosphorylation. For longer-term energy.

ATP production in substrate-level phosphorylation vs. oxidative phosphorylation

Substrate-level: around 2 ATP
Oxidative: around 26 or 28 ATP

Where does substrate-level phosphorylation occur?

In the cytoplasm

In substrate-level phosphorylation, high-energy phosphate groups are directly transferred from _________________________ to ADP.
How does this work in glycolysis and the Krebs cycle?

Phosphorylated substrates.
This normally occurs twice in glycolysis, and once in the Krebs cycle per molecule of glucose.

How is a H+ concentration gradient created in oxidative phosphorylation?

Energy from the oxidation of food is used to pump H+ across the mitochondrial membrane

True or False:
As H+ flows back through ATP synthase membrane channel protein, energy from this flow is used to phosphorylate ADP into ATP

True

What can glucose be termed in the body?

Our blood sugar

When glucose enters a cell, what is it phosphorylated into?
What does this allow it/prevent it to do?

Phosphorylated into glucose-6-phosphate.
Prevents it from leaving the cell once it has already entered.

How does glucose enter a cell?

Facilitated diffusion

Why is it important that glucose can't leave the cell once it has entered?

It keeps the intracellular glucose concentration low. ensuring continued glucose entry through diffusion

What does this reaction represent:
C6H1206 + 6O2 -> 6CO2 + 30 ATP + heat

The catabolizing of glucose

Complete glucose catabolism requires 3 pathways:

1. Glycolysis and formation of acetyl CoA
2. Citric acid cycle (Krebs)
3. Electron transport chain (ETC) and oxidative phosphorylation

Glycolysis is a ___-step pathway

10

Glycolysis is (anaerobic/aerobic)

Anaerobic

In glycolysis, a glucose molecule (6C) is broken into _________________ molecules (3C)

Two pyruvic acid molecules

In glycolysis, how many hydrogens does glucose lose?
Where do they go/what do they produce?

Loses 4 hydrogens. They bind to 2 molecules of NAD+, producing 2 NADH + 2H+

What is the net gain in glycolysis?
Why is this?

Net gain of 2 ATP.
Glycolysis makes 4 ATP, but it costs 2 to start

The supply of NAD+ is limited. How does glycolysis continue despite this?

NADH must donate its accepted hydrogen atoms to become NAD+ again. This allows it to pick up more H+ for the continuation of glycolysis

What does NADH do during glycolysis if no oxygen is present? What does this allow for?

NADH returns its hydrogen to pyruvic acid which forms lactic acid.
This allows NAD+ to continue to act as an electron acceptor

If there is lactic acid present during glycolysis and oxygen becomes available within the cell, what happens?

Lactic acid is oxidized back into pyruvic acid and enters aerobic pathways

Where does the Krebs cycle occur?

In the mitochondrial matrix

What is the citric acid cycle fueled by?

Pyruvic acid from glucose breakdown and fatty acids from fat breakdown

Pyruvic acid is a charged molecule that can't diffuse across the mitochondrial membrane. What does this mean for its transportation?

It must be actively transported into the mitochondria

Krebs cycle:
Once inside the mitochondria, pyruvic acid enters a ____________ phase.
Explain this phase

Transitional phase.
This is where each pyruvic acid is converted to acetyl coenzyme A (acetyl CoA) if oxygen is available.

What does "glycolytic pathway" mean?

Another word for glycolysis

When entering the mitochondria, what does pyruvic acid gain/lose?

Loses a C as CO2 and two H atoms

Where does the energy used for the electron transport chain come from?

Energy from FADH2 and NADH
(move H+ from the mitochondrial matrix to the inter-membrane space)

What does ATP synthase do in the electron transport chain?

ATP synthase phosphorylates ADP to ATP as the H+ diffuses

What is glycogenesis?
When/why does it happen?

Process that forms glycogen from glucose.
This happens when we have too much glucose. Muscles do this, and the liver does it often.

ATP can't be used to store energy long-term. How do we get long-term energy from glycogen?
Where does this process occur?

Glycogen synthase catalyzes the attachment of glucose into a chain of glycogen.
This mainly occurs in the liver and skeletal muscle.

What is glycogenolysis?

Breaks down glycogen

How do cells react in response to blood glucose levels dropping?

They split glycogen into glucose molecules

In most body cells, glycogen in broken down to:

Glucose-6-phosphate

How does glycogen transition from the liver to glucose in the tissues

Glycogen is broken down in the liver into glucose, and it's transported in the blood to all tissues of the body

What is gluconeogenesis?
What is its purpose?

Process that forms glucose from non-glucose molecules, such as glycerol or amino acids.
It maintains blood glucose when dietary sources and glucose reserves begin to deplete. It protects the body from hypoglycemia (low blood sugar) - especially the nervous system.
* Turning something new into glucose, even in the absence of carbohydrates

When glucose is produced in the liver, where does it go?

It enters the bloodstream to be used elsewhere in the body

When glucose is produced in the muscle, where does it go?

It is used almost immediately by nearby muscle tissue

True or False: Individual cell activity is unimportant due to its insignificance in size.

False.
Cellular activity is important on the individual level as well as group level.

What are biochemical activities of a cell dictated by?

Their shape and form, as well as subcellular structures

Where do cells come from?

Other cells

True or False:
Different cells (muscle, nervous, fat, etc.) have different DNA directing them to do their different roles

False.
All cells have identical DNA, but different cells use this DNA differently.

What are extracellular materials?

Substances found outside of the cell

What are examples of extracellular fluid?

Interstitial fluid, blood plasma, cerebrospinal fluid

What is the extracellular matrix?
Where does it come from?

Jellylike substance of proteins and polysaccharides that help hold cells together.
It's produced by cells themselves.

What is the primary role of the cell membrane?

To control what enters and exits the cell, as well as what happens within.
It's an active barrier that separates intracellular fluid and extracellular fluid.

What is the fluid mosaic model?

A model that describes the cell membrane. It consists of a bilayer of fluid lipids (98%) within which are a variety of proteins

What is a phospholipid bi-layer?

Two layers of phospholipids that make up the plasma membrane.

What is the primary form of movement within the phospholipid bi-layer?

Horizontal movement, given that there is water in its environment to keep it in formation (with hydrophobic tails pointing inwards towards one another)

Integral membrane proteins

Go all the way through the plasma membrane.
Involved with transport as channels or carriers.

Peripheral membrane proteins

Are attached to either the inside or the outside of the cell.
Attach to integral proteins or to phospholipids, that may function as enzymes or in mechanical functions of the cell.

The glycocalyx

Fuzzy and sticky carbohydrate-rich are sticking out of a cell's surface that acts as a biological marker for identification among other cells.
Some sugars are attached to lipids (glycolipids), and some to proteins (glycoproteins).

What type of permeability does a plasma membrane have?

Selective permeability

How does the electrochemical gradient of the plasma membrane work?

On either side of the membrane, there are ions (electrolytes). Negatively charged ions are attracted to positive ones and vice versa. But, these ions cannot cross the membrane unless they are permitted to (unless a "door" opens).

What composes a lipid bilayer (substances in %)

75% phospholipids
20% cholesterol
5% glycolipids

The tails of phospholipids are hydrophobic, making them (a) (polar/nonpolar)
The heads of phospholipids are hydrophilic, making them (b) (polar/nonpolar)

(a) nonpolar
(b) polar

What are glycolipids?

A sugar coating on the outside of a cell/the cell membrane for identification

What is an ion channel?
Example?
Is it integral, peripheral, or both?

For charged substances.
Forms a pore through the membrane which a specific ion can flow through. Most plasma membranes have specific channels for many common ions.
Example: Although both are charged, the body recognizes K and Na differently and they have different channels.
Integral.

What is a carrier?
Is it integral, peripheral, or both?

For bigger substances.
Transports a specific substance across the membrane by undergoing a change in shape. AKA transporters.
Integral.

What is a receptor?
Example?
Is it integral, peripheral, or both?

For chemical signals.
Recognizes a specific ligand (chemical signal) and alters cell's function in some way.
Example: Most hormones don't enter cells, they just bump into them, causing the receptor to change slightly and then it activates a message into the cell.
Integral.

What is an enzyme?
Two examples?
Is it integral, peripheral, or both?

Catalyzes reactions inside or outside the cell (depends on which direction the active site faces).
Example: Lactase can hydrolyze lactose so it can be easily transported into the cell.
Example: Poly/disaccharides are too large, so enzymes can turn them into monosaccharides.
Both integral and peripheral.

What are linkers?
Is it integral, peripheral, or both?

Bends into the shape that the cell needs.
Anchors filaments inside and outside the plasma membrane, providing structural stability and shape for the cell. It could also help the cell move and link cells together.
Both integral and peripheral.

What is a cell identity marker?
Example?

Helps the immune system determine if the cells are self or non-self.
Example: Blood type markers.

What does chemical signaling involve?

The binding of a chemical signal (ligand) to a membrane receptor. When the ligand binds, the receptor protein changes shape and becomes activated. This results in the initiation of a cellular response.

True or False: Ligands only have one primary role for chemical reactions, similar to antibodies. This is why cells have so many ligands.

False.
The same ligand can cause different responses in different cells depending on the chemical pathway that the receptor is part of (reactions are up to the receptor and not the ligand).
Example: The same hormone affecting muscles vs. the GI tract vs. the brain differently.

What are G protein-linked receptors?
Example?

A specific type of chemical signaling.
Indirectly cause cellular changes by activating G proteins. G proteins can then affect ion channels and activate other enzymes.
It essentially causes a chain reaction of signals.
Example: About 30% of drugs use this method, which is why you only need a small amount of drug for a big impact. One cell messages ten, then those ten each message 100, then those hundred each message 1000, etc.

What are CAMs?
What are their functions?

Cell Adhesion Molecules, part of the glycocalyx.
- Anchor cells to extracellular matrix/each other.
- Assist in movement of cells past one another.
- Attract immune cells to injured/infected areas.
- Stimulate synthesis/degradation of adhesive membrane junctions (ex. tight junctions).
- Transmit intracellular signals to direct cell migration, proliferation, and specialization.

Tight junctions

Integral proteins that join adjacent cells to prevent molecules from passing through the extracellular space between cells

Desmosomes

"Cell velcro"
Scattered attachments along adjoining cells that reduce the chance of cells tearing apart when a tissue is stressed

Gap junctions
Example?

Hollow cylinders of protein between cells that allow some small molecules to pass between adjacent cells, and are often used to conduct action potentials directly from cell to cell.
Example: This is how the heartbeat is coordinated (it's one big contraction instead of many small ones)

Explain the selective permeability of the cell membrane - which substances can pass through?

A molecule will diffuse through the membrane if it's:
- Lipid-soluble
- Small enough to pass through a channel
- Assisted by a carrier protein

True or False: Growth of a cell is individual and only relies on itself and a non-toxic environment.

False.
The growth, maturation, and division of a cell in its environment depends on itself, as well as the other cells that surround it.
Example: Putting the foot bud of an chick embryo onto the extremity of its wing will cause it to have a mix of foot-like and wing-like characteristics.