Basic Concepts of Metabolism. Flashcards
In which cells does metabolism take place?
In almost every cell.
Why do cells take part in metabolism?
It is the way that cells gain energy to build organelles and perform various functions.
What are the 2 steps that need to occur in metabolism?
The extraction of energy from food.
Using nutritional energy to build various organelles and for other bodily tasks such as movement.
What are the steps that occur in metabolism called?
Catabolism.
Anabolism.
What is catabolism?
Catabolism produces energy by taking the nutrients from carbs, lipids and proteins and breaking them down into their smallest components.
What is anabolism?
Anabolism uses the energy produced by catabolism to make proteins and other organic structures.
In what form is the energy produced by catabolism?
ATP.
Is catabolism an oxidative or reductive process?
Oxidative.
What are the high energy molecules that are obtained by catabolism?
ATP.
NADH.
NADPH.
FADH2.
How can you tell that ATP, NADH, NADPH and FADH2 are high energy molecules?
Because they all have a lot of hydrogens.
How many stages are there in catabolism?
3.
What is the 1st stage of catabolism?
The digestion of nutrients which are broken down into their pre-cursor molecules.
What nutrients are broken down via catabolism?
Proteins.
Fats.
Carbohydrates.
What are the pre-cursor molecules for proteins?
Amino acids.
What are the pre-cursor molecules for carbohydrates?
Carbohydrates are polysaccharides so their pre-cursor molecules are monosaccharides.
What are the pre-cursor molecules for fats?
Glycerol and fatty acids.
Why are nutrients from the diet broken into their component parts?
Because only the component parts are absorbed through the small intestine into the bloodstream.
Is stage 1 of catabolism extracellular or intracellular?
Extracellular as it occurs in the digestive system.
What happens when the component parts of nutrients are absorbed?
The component parts are absorbed by the intestinal mucosal cells into the bloodstream where they are transported to various cells.
Is the 2nd stage of catabolism extracellular or intracellular?
Intracellular.
What occurs during the 2nd stage of catabolism.
Each individual component is broken down to form a common intermediate.
What is the common intermediate formed in the 2nd stage of catabolism?
Acetyl-CoA which is a 2 carbon molecule.
Does catabolism occur in a specific organelle within the cell?
No.
Each class of organic molecule is broken down via a different pathway and in a different organelle.
Is acetyl CoA formed by the components of fats, carbs and proteins?
Yes.
Acetyl-CoA is formed by multiple dietary components which have different pathways.
What organelle is responsible for the formation of acetyl CoA?
Acetyl CoA is always formed in the mitochondria. It is always the final step of the pathway for each component.
Where does stage 3 of catabolism occur?
In the mitochondria.
What is the 3rd step of catabolism?
The further oxidation of acetyl-CoA to a usable form of energy (ATP) and a waste product (CO2).
What is always the final stage of step 2 of catabolism?
The formation of AcoA in the mitochondria.
Do the first 2 steps of catabolism create any high energy products?
Yes.
They create many high energy products such as NADH, NADPH and FADH2 which are also converted to ATP.
What is anabolism?
The process by which the body uses precursors and turns them into cellular macromolecules.
How does the body obtain the precursors that are used in anabolic processes to create cellular macromolecules.
From the diet.
They can be synthesised by the body.
They can be recycled by the body.
Name some cellular macromolecules that are formed by anabolism?
Proteins.
Nucleic acids.
Polysaccharides.
Does anabolism require energy?
Yes.
Does catabolism require energy?
No.
How does anabolism get the energy required to build macromolecules?
From the high energy molecules that are produced via catabolism.
What are the products from catabolism reduced to after anabolism?
ADP.
NAD+.
NADP+.
FAD.
Does metabolism occur in 1 organ or in many organs?
In many organs.
Why must metabolism be regulated?
Because, it occurs in many organs and they need to synchronise work load.
How is metabolism in different organs controlled?
There is a communication system that organs use to tell other organs how hard to work.
What are the 2 types of signal that cells can use to communicate with each other during metabolism?
Intracellular signal.
Intercellular signal.
What is an intercellular signal?
Signals between different cells.
Give an example of an intercellular signal?
When glucose levels rise in the body, the pancreas secretes insulin into the bloodstream.
Insulin is sent to the liver cells and will be received by a specific receptor on the cell membrane.
The receptor will then cause an intracellular response within the individual liver cells.
What is a primary messenger?
It is an intercellular signal that will attach to a receptor on the cell membrane.
This will cause the release of an intracellular messenger.
What is a secondary messenger?
When a primary messenger binds to the membrane receptor, the receptor will release an intracellular messenger or 2nd messenger to go to the nucleus.
Can any primary messenger bind to any cell membrane receptor?
No.
Each type of stimulus that is released by a cell will have a unique receptor to which it binds on the target cell.
What is an intracellular signal usually a response to?
An intercellular signal.
What will an intracellular signal do?
It will travel into the interior of the cell and will tell the various organelles what to do.
What is signal transduction?
The process of converting an intercellular signal into a intracellular signal.
What are the 3 types of intercellular signal?
Synaptic signalling.
Endocrine signalling.
Direct contact signalling.
What is synaptic signalling?
When a synaptic cell will produce neurotransmitters aimed at a specific target cell.
The neurotransmitter will find a specific receptor on the target cell which elicits the production of a second messenger and a change inside the cell.
What kind of cells are common synaptic cells?
Nerve cells.
What kind of molecules are used for endocrine signals?
Hormones.
How does endocrine signalling work?
A hormone is released by a cell and will travel through the bloodstream to a specific receptor on a target cell.
What is direct contact signalling?
Where 2 adjacent cells can communicate via contact between gap junctions or cell surface receptors.
What do cells need to signal via direct contact?
Both cells must have compatible receptors or junctions on their cell membranes.
What are the 4 types of intercellular signal receptors?
Gated ion channels.
Receptor enzyme (catalytic receptor).
G protein coupled receptors (GCPRS).
What is an intracellular receptor that can receive intercellular signals?
Steroid receptors.
Where is a steroid receptor located?
In the nucleus.
How will a steroid enter the nucleus?
It will cross the cytoplasmic membrane.
Once in the cytoplasm it will bind to a specific receptor and form a complex.
The complex will then cross the nuclear membrane and enter the nucleus.
What happens to the steroid receptor complex once they enter the nucleus?
Once in the nucleus, it will bind to an enhancer region of DNA.
This activates a specific gene in the promoter region.
The activated gene will produce mRNA that will lead to a gene product such as a protein.
Do all the messengers that travel to steroid receptors bind to receptors in the cytoplasm?
No
Some will cross directly into the nucleus and bind to a receptor there.
Some may bind directly to DNA.
What molecule tends to be the primary messenger that are received by steroid receptors?
Hormones.
Why must hormones be lipophilic?
Because they must cross the cytoplasmic membrane.
How do gated ion channels work?
They are channels within the cell membrane that will open or close in response to an intercellular signal.
How will an intercellular signal change a gated ion channel?
The conformation will change as it is either opening or closing the channel.
What is a receptor enzyme also known as?
A catalytic receptor.
How does a catalytic receptor work?
The binding of the signal induces intracellular changes within the enzyme.
Describe the location of a catalytic receptor?
The receptor for this enzyme is on the extracellular side of the membrane.
The enzyme is on the cytoplasmic side of the membrane.
Where are GCPR receptors located?
In the cell membrane.
How do cell membrane receptors work?
An extracellular signal binds to a GCPR.
This causes the receptor to bind to a G protein.
This will activate an enzyme within the G protein that will produce a second messenger to elicit an intracellular response.
Where is the G-protein located when the GCPR binds to it?
In the cytoplasm.
What type of receptor is the only one that isn’t located in the cell membrane?
Steroid receptors.
What kind of binding domains do membrane bound receptors have?
Extracellular binding domains.
Which type of signal and receptor will usually cause an up-regulation in gene expression?
Steroid hormones and steroid receptors.
What kind of cells often use gated ion channels?
Neurotransmitters.
How many subunits make up a receptor enzyme?
4.
What are the 4 subunits of a receptor enzyme?
2 alpha.
2 beta.
What subunits make up the receptor part of a receptor enzyme?
The 2 alpha subunits.
What subunits make up the enzymatic part of a receptor enzyme?
The 2 beta subunits.
The enzyme of a receptor enzyme is what class of enzyme?
A kinase.
It will phosphorylate amino acids.
How does a receptor enzyme for a 2nd messenger?
It will phosphorylate a tyrosine residue which will then travel to other intracellular proteins and transfer the phosphate group.
What is a common signal used by gated ion channels?
Acetyl-choline.
What is a common signal used by receptor enzymes?
Insulin.
Which type of receptor is made up of 7 transmembrane helices?
A GPCR.
Why are G proteins called G proteins?
Because they interact with GDP and GTP.
How does a GCPR produce its 2nd messenger?
Once the G protein is activated, it will produce a small, organic molecule which is the 2nd messenger.
How many types of 2nd messenger can be produced by a GPCR?
2.
What are the 2 methods of production of 2nd messengers that are produced by GPCRs?
Adenylate cyclase system.
Calcium/phosphatylinositol system.
What is the 2nd messenger that is produced by the adenylate cyclase system?
Cyclic AMP (cAMP).
What is the 2nd messenger that is produced by the calcium/phosphatylinositol system?
IP3, DAG, Ca2+.
Define a 2nd messenger?
A small, organic molecule that is produced in the cytoplasm in response to the activation of a cell surface receptor.
What will a 2nd messenger do once it is formed?
It will cause a cascade of intracellular events resulting in a cellular response.
Are 2nd messenger proteins?
No.
Will a GPCR only produce 1 second messenger?
No, they will produce many.
Is the 2nd messenger present in the cell when the primary messenger binds to the receptor?
No.
It is formed after the primary messenger has bound to the receptor.
What kind of receptor is involved in the adenylate cyclase system?
A GPCR.
What stimuli can start the adenylate cyclase system?
Epinephrine/norepinephrine or glucagon.
Will epinephrine/norepinephrine or glucagon bind to the same GPCR?
No.
Glucagon and epinephrine will bind to different GPCRs, but both will start the same pathway.
What is the 2nd messenger in the adenylate cyclase system?
cAMP. Cyclic AMP.
How is the adenylate cyclase system triggered?
Epinephrine or glucagon will bind to their receptor.
This will activate the GPCR.
What receptor will glucagon bind to to activate the adenylate cyclase system?
The glucagon receptor.
What receptor will epinephrine/norepinephrine bind to to activate the adenylate cyclase system?
The beta adrenergic receptor.
Where will the glucagon/epinephrine receptor for the adenylate cyclase system be located?
On the extracellular side of the cell membrane.
What happens once the beta adrenergic or glucagon receptor has been activated?
The GPCR will relay the message from the signal to the G protein.
The signal will cause the alpha subunit of the G protein to replace GDP with GTP.
Where is the G protein that is interacts with a GPCR located?
In the cytoplasm.
What are the 3 subunits that make up a G protein?
Alpha.
Beta.
Gamma.
Is the alpha subunit of the G protein bound to anything?
Yes, it is bound to GDP.
What is the alpha subunit called once it is bound to GTP?
The GS alpha subunit.
What happens to the alpha subunit once it has replaced GDP with GTP?
The GS-alpha subunit will then dissociate from the beta and gamma subunits.
It will then move towards and bind to the target enzyme.
What is the target enzyme for the GS alpha subunit?
Adenylate cyclase
What is the activated form of the alpha subunit in the adenylate cyclase system?
The GS alpha subunit.
How is adenylate cyclase activated?
It is activated when the GS alpha subunit binds to it.
What happens once adenylate cyclase is activated?
It will use ATP to catalyse the formation of cAMP.
What is cAMP?
It is the second messenger in the adenylate cyclase system.
What will cAMP do once it has been formed?
It will travel through the cytoplasm to activate protein kinase A (PKA).
What will protein kinase A do once it has been activated?
PKA is an enzyme that will phosphorylate many different enzymes within the cell.
What causes the cellular response to the adenylate cyclase system?
When PKA phosphorylates enzymes, it will lead to a cellular response.
How is the adenylate cyclase system stopped?
Phosphodiesterase will hydrolyse cAMP to 5-AMP and PKA will be deactivated.
What is the stimulus for the beta adrenergic receptor?
Norepinephrine or epinephrine.
What is the G protein for the beta adrenergic receptor?
GS alpha.
What is the effector enzyme for the beta adrenergic system?
Adenylate cyclase.
What is the target of the second messenger for the beta adrenergic system?
Protein kinase A.
How will glucagon and epinephrine lead to differences in the beta adrenergic system?
Glucagon will bind to the glucagon receptor but will activate exactly the same system.
What kind of cell receptors have extracellular binding domains?
GPCRs.
Gated ion channels.
Enzyme linked receptors.
What is the only type of receptor that has its messenger enter the cell?
Steroid receptors.
Is the alpha-1 adrenergic receptor similar to the beta adrenergic receptor?
No. They are different.
The only similarity is that they are both GPCRs.
What will activate the alpha-1 adrenergic receptor?
Norepinephrine or epinephrine.
Does the alpha-1 adrenergic receptor use the same G protein as the beta adrenergic receptor?
No.
It uses the alpha subunit of the G protein but it is called the GQ alpha subunit.
Does the GQ alpha subunit activate the same second messenger as the GS alpha subunit?
It activates a different target enzyme and produces a different 2nd messenger.
What is the pathway that is triggered by the alpha-1 adrenergic receptor called?
Phosphoinositide system.
Why is the pathway that is activated by the alpha-1 adrenergic receptor called the phosphoinositide system?
Because the process will cleave phosphoinositol 4,5-bisphosphate to form IP3 and DAG.
What can phosphoinositol 4,5-bisphosphate be abbreviated to?
PIP-2.
What will cleave PIP-2?
Phospholipase C.
What are the 2nd messengers that are produced by the phosphoinositide system called?
IP3.
Calcium ions.
DAG.
What is the substrate for phospholipase C?
PIP-2.
What is step 1 of the phosphoinositide system?
The binding of epinephrine or norepinephrine to the alpha-1 adrenergic receptor.
What happens once epinephrine has bound to the the alpha-1 adrenergic receptor?
It causes the alpha subunit of the G protein to swap its GDP for GTP.
What happens once the alpha subunit of the G protein has bound to GTP in the phosphoinositide system?
It will dissociate from the rest of the G protein.
What is the activated form of the alpha subunit called in the phosphoinositide system?
The GQ alpha subunit.
What happens once the GQ alpha subunit has dissociated from the G protein?
It will travel to its target enzyme.
What is the target enzyme of the GQ alpha subunit?
Phospholipase C.
How is phospholipase C activated?
By the binding of the GQ alpha subunit.
What happens once phospholipase C is activated?
It will travel down the cell membrane until it finds PIP-2.
What happens once phospholipase C finds PIP-2?
It will cleave PIP-2 to form 2 second messengers.
What are the 2 second messengers that arise as a result of the cleaving of PIP-2?
DAG.
IP3.
Is DAG or IP3 a water soluble molecule?
IP3 is water soluble.
Why does IP3 need to be water soluble?
So it can travel into the cytoplasm.
Where is PIP-3 located?
In the cell membrane.
Will DAG travel into the cytoplasm once it has been formed?
No.
It will stay in the membrane.
What increases the amount of IP-3 in the cell?
The cleavage of PIP-2.
What will IP-3 do once it has been cleaved from PIP-2?
It will travel through the cytoplasm and bind to the endoplasmic reticulum which causes a release of calcium ions.
Are the calcium ions that are released from the ER by IP-3 considered a 2nd messenger?
The calcium ions are an additional 2nd messenger as they were not present in the cytoplasm when this pathway started.
What happens once the calcium ions have been released from the ER?
They and DAG will bind to a membrane bound enzyme
called protein kinase C.
What happens once phospholipase C has been activated?
It will phosphorylate specific enzymes and this will lead to a cellular response.
What is the stimulus for the alpha-1 adrenergic receptor?
Epinephrine/norepinephrine.
What is the G protein for the alpha-1 adrenergic receptor?
The GQ alpha subunit.
What is the effector enzyme in the phosphoinositide system?
Phospholipase C.
What is the target of the effector enzyme in the phosphoinositide system?
PIP-2.
What are the 2nd messengers in the phosphoinositide system?
Calcium ions, DAG and IP-3.
What is the target of the 2nd messengers in the phosphoinositide system?
Protein kinase C.
