Practice English Speaking&Listening with: Metabolism

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hello everyone today we're going to talk about metabolism when we think of

metabolism we think of two main reactions anabolic reactions and

catabolic reactions anabolic reactions are reactions that would synthesize

large molecules from smaller ones for example proteins are made out of amino

acids so if we take amino acids and link them together to create something large

such as a protein that would be considered an anabolic reaction a

catabolic reaction on the other hand this is a reaction where you break down

larger molecules into smaller ones so if you eat protein and you go ahead and you

digest the protein and you break it down into its building blocks which are the

amino acids that will be considered a catabolic reaction anabolic and

catabolic reactions are reversible anabolic reactions we usually go through

a lot of anabolic reactions during a state known as the fed state or the

absorptive state and that's the period of time following a meal so you've

already had a meal and so you already digested your food so now

this time you will be absorbing and storing those

nutrients and you will actually start building new larger molecules for

example you just ate a meal and so you just broke down some of the carbs that

you just ate you broke down some of the proteins that you've just eaten what are

you going to do with all of that glucose now in your body and all of

these amino acids in your body you are going to use them for energy but

whatever is going to be left over you're going to actually start turning them

into larger molecules so you're going to start turning the excess glucose in your

body into larger molecule known as a glycogen you

can take the excess amino acids in your body and make proteins so therefore we

say that during this state we are going to be going through a lot of anabolic

reactions catabolic reactions are mostly done within a period known as the

fasting state or the post absorptive state so when you are fasting that's a

time when you don't really have enough nutrients in your bloodstream because

you are fasting and so what you're going to do to go ahead and get some energy

your body is going to take those larger molecules those reserves that you have

inside of your body and your body is going to start breaking it down so that

you can get some energy for example if you've been fasting and you haven't eaten

anything in a while your body is going to take the stored glucose which is

glycogen and it's actually going to start breaking it down so that you can

get energy out of it and so therefore we say that when we are fasting we go

through a lot of catabolic reactions our diet usually consists of fats carbs and

proteins when we go through a catabolic reaction we break down those

macromolecules into their smaller building blocks so fats are going to be

broken down into fatty acids and glycerol carbs are going to be broken

down into sugars usually glucose proteins are going to be broken down

into amino acids now the plasma amount of glucose so our plasma glucose

concentration is the most closely regulated one because glucose turns out

that glucose is the only fuel your brain can metabolize

except in times of starvation your brain can actually also use something else

known as ketone bodies otherwise your brain hugely relies on glucose and so

therefore if this image right here represents the amount of glucose that we

should normally have in our blood plasma and all of a sudden your blood glucose

drops way below that normal level who's going to have access to that glucose

only the brain now if we have normal levels of glucose then your brain is

going to have access to it but also all of your other tissues they're going to

also have access to that glucose what if we have excessive amounts of glucose in

our bloodstream what's going to happen to all of that glucose if you have

excessive amounts of glucose then it can actually be excreted in your urine

or if you have excessive amount of glucose you can actually start storing

it as fat and that process would be known as lipo Genesis lipo coming from

the word lipids which are fats Genesis meaning to make so excess glucose can

turn into fat and get stored in your body as fat what else can happen to

excess amount of glucose we can go ahead and store it in the form of glycogen the

process of converting the glucose into glycogen is known as glycogenesis again

Genesis meaning to make and so we are making glycogen glycogen is usually

stored in your liver and in your skeletal muscles okay so we've already

talked about what can happen if your glucose levels are in excessive amounts

well let's go ahead talk about what could happen if let's

say you are fasting so if you're fasting your glucose levels in your bloodstream

are actually going to be pretty low so if your glucose levels in your

bloodstream are pretty low what is your body going to do well your body is

actually going to go and access the glycogen pull out the glycogen out of

your liver and out of your skeletal muscles and your body is actually going

to start breaking down the glycogen back into glucose so that you can start

increasing the glucose levels in your bloodstream that process of breaking

down the glycogen back into glucose is known as glycogenolysis if we break the

word down glycogen is right here and then the suffix of the word is lysis

which means break down so glycogenolysis is when we break down the glycogen into

glucose now also if your blood glucose levels it's pretty low other than going

through glycogenolysis so we can actually go through something else

as we said proteins are made out of amino acids we can actually take the

amino acid and convert it into glucose and that process is known as gluconeo-

Genesis let's break the word down gluco meaning glucose neo meaning new genesis

meaning to make so we are making new glucose and we use that term

gluconeogenesis usually when we are making glucose out of a none

carbohydrate source so in this case if we are using amino acids to make glucose

that's a none carbohydrate source right there and so that process is known as

gluconeogenesis amino acids usually a we have amino acids usually they are

going to make proteins so as you can see we can recycle our amino acids and make

proteins but in case as I said you have very low levels of glucose

then amino acids can go ahead and convert into glucose a via reaction that

they will go through if we take a look at this image right here we see that

fats are also going to be broken down and used by your tissues so your tissues

can also use fats and break them down and get a lot of energy out of them

Glycogenolysis is the process of breaking down glycogen so if our glucose levels in our

bloodstream is pretty low we go through glycogenolysis so that we can get the

glucose which is then going to be used to make ATP which is energy now

when glycogen is broken down glycogen can break down into plain glucose and

that's ten percent of the time or ninety percent of the time when glycogen breaks

down we get what's known as glucose 6-phosphate

now glucose 6-phosphate is what's going to be used during our cellular respiration

to make energy and so therefore if glycogen is broken down into plain glucose

we must convert that glucose into glucose 6-phosphate by adding a

phosphate to that plain glucose breaking down glycogen into glucose

6-phosphate it's going to be faster for us to use it directly to make energy

versus if we break down glycogen into plain glucose and then we have to

convert that glucose into glucose 6-phosphate it's going to take longer

and it's going to take more energy from your cells to actually do that but at the

end of the day after we get that glucose 6-phosphate

either directly or by extra steps that glucose 6-phosphate

will enter into the glycolysis process during cellular respiration and we go

ahead and we make lots of ATP as we said proteins are made out of amino acids so

when you eat protein you break down the protein into amino acids those amino

acids can further break down so they can go through more catabolic reaction and

break down further into ammonia and a bunch of organic acids that process

is known as deamination now those organic acids that would result can

actually be used by your cellular respiration reaction so we can use them

to make energy and also if your glucose levels in your bloodstream is pretty low

then we can use those amino acids after we break them down and they will go

through more reactions we can use them to convert them into glucose also if you

have let's say lots and lots of amino acids in your bloodstream what can we do

with all of that excessive amount of amino acids they can actually be turned

into fat so you have to be aware of how much protein you are consuming

because if you are consuming way too much protein than your body really needs

then all of that excessive amino acids from the protein can actually be turned

into fat that ammonia by the way that would result is

toxic so your body converts it into urea and eventually your body will excrete it

out let's say that you have an enzyme enzyme number one right here and this

enzyme it's job is to speed up the reaction of converting a substrate a

into substrate B but let's say you also have another enzyme enzyme number two

that would speed up the reaction of converting B back into A now if you have

equal amounts of those enzymes being released at all times you're never going

to have a net amount of A and you're never going to have a net amount of B

because you are always going to be going through that cycle back and forth

converting A into B and right away converting it back into A so if you want

to control how much substrate A or how much substrate B you want to have you

really need to control how much of those enzymes you are releasing so let's take

a look at an example let's say that we are in a fed state or basically

absorptive state that's when we are in a state where we have just eaten a meal

now if you've just eaten a meal what's gonna happen to your glucose levels well

your glucose levels are going to start to increase okay after eating a meal now

high glucose levels in your bloodstream that's going to stimulate your

pancreatic cells to produce a hormone known as insulin insulin is going to

start decreasing your glucose levels in your blood stream

how is insulin going to do that well insulin is going to stimulate a bunch of

enzymes and those enzymes are going to take the glucose in your bloodstream and

start converting it and storing it in your liver and in your skeletal muscles

in the form of glycogen so insulin is going to increase the levels of glycogen

in your blood stream because it's going to be

promoting the conversion of glucose into glycogen now also insulin is going to

inhibit the enzymes that will break down glycogen into glucose because you don't

want to increase your glucose levels the whole point of producing insulin was to

decrease your glucose levels and so insulin is going to prevent the enzymes

that will break down glycogen back into glucose let's say that right now you are

fasting if you are fasting what does that mean it means that your glucose

levels are going to start to drop if your glucose levels start to drop your

body would want to increase your glucose levels and so your body is not going to

produce insulin low glucose levels are going to stimulate your pancreas to

produce another hormone that hormone is known as glucagon glucagon is going to

do the exact opposite of insulin glucagon is actually going to access the

glycogen that you have stored in your liver and in your skeletal muscles and

it's going to stimulate a bunch of enzymes that will break down the

glycogen into glucose so that you can increase the glucose levels in your

bloodstream and glucagon is also going to inhibit the enzymes that will try to

convert the glucose back into glycogen because right now your body wants to

increase the glucose and not really store it and so therefore when glucagon

is released your net glucose synthesis is going to increase because glycogen is

going to start breaking down into glucose when insulin on the

other hand is being released your net amount of glycogen is going to increase

because your body would want to store the excess glucose as glycogen so as we

said your pancreas has the ability to secrete and release two different

hormones insulin and glucagon insulin is going to be produced by cells in your

pancreas known as beta cells and glucagon is going to be released by

cells in your pancreas known as alpha cells and we know now that when is

insulin going to dominate insulin is going to dominate after you've eaten a

meal right so when you are in the fed State glucagon is going to be dominated

when you are in the fasting state so when you're fasting in your glucose

levels drop glucagon is going to be the dominant hormone being released so that

it can help you increase the glucose levels and so therefore during the

fasting state glucagon is going to dominate and insulin is not going to be

released and vice versa after you eat insulin is going to be produced and

glucagon is going to be inhibited okay let's say that you are in a fed state

basically you've just eaten if you've just eaten a meal then we know that your

glucose levels are going to increase and if your glucose levels increased then

the hormone that's going to dominate is insulin insulin is going to try to

decrease your glucose levels in your bloodstream so if we take a look at this

graph right here and this dotted line is showing you your glucose concentration

after eating the meal you'll notice that after you eat a meal your glucose

concentration increase and so if your glucose levels after

eating a meal increases the hormone that's going to increase in production

is going to be insulin because insulin would want to try to lower that glucose

level in your bloodstream the hormone after a meal that's going to be pretty

low is glucagon because glucagon what it does is increase your glucose levels and

right now your glucose levels are already high so

you don't want to produce glucagon so after a meal insulin is going to be

pretty high and glucagon is going to be pretty low in your bloodstream

now what insulin does as we said it's going to try to decrease your glucose

levels it's going to try to let your cells absorb the glucose and we will

talk about how is that going to be done and it's going to try to increase your

glycogen synthesis how it's going to try to as I said stimulate a bunch of

enzymes and those enzymes are going to convert the excessive glucose now that

we have in our bloodstream into glycogen and that glycogen is going to be stored

in our liver and in our skeletal muscles if you have too much glucose in your

bloodstream insulin is going to increase the fat

synthesis process and so therefore we have to be careful about how many times

we're eating or how much we are eating because if you if someone constantly

eats even though let's say they are eating healthy things but you are still

constantly eating your glucose levels keep spiking up then insulin is going to

keep spiking up and then all of that glucose is actually going to start

getting stored in the form of fat insulin also increases our protein

synthesis process now on the other hand if we are

fasting and our glucose levels drop so if your glucose levels drop you

definitely don't want to produce insulin because insulin is just going to make

things even worse and so your pancreas during fasting your pancreas is going to

produce the hormone known as glucagon glucagon is going to do the opposite

glucagon is going to go to the stored glycogen in your liver and in your

skeletal muscles and it's going to break it down of the process known as

glycogenolysis as we said and it's going to break it down into glucose to

increase the glucose levels in your bloodstream

glucagon is also going to increase the process known as gluconeogenesis

if we remember gluconeogenesis is the process of making glucose out of none

carbohydrate sources so if your glucose levels in your bloodstream

their levels are really really low your body will go ahead and take some of the

amino acids you have and convert those amino acids into glucose another thing

your body is going to do to try to increase your glucose levels is that

glucagon is going to help the process of making ketone bodies how do we make

ketone bodies out of fatty acids so fatty acids you get fatty acids by

breaking down fat so your body is going to break down the fat for you you get

fatty acids out of it you take those fatty acids and you convert them into

glucose or sorry you don't convert them into glucose you convert them into

something known as ketone bodies and those ketone bodies are going to be used

by your brain so as we said your brain highly depends on glucose as its major

fuel source so if your glucose levels are really low as we said your body can

either take the amino acids convert them into glucose but if that's not enough

your body is going to take the fatty acids and convert those into ketone

bodies and then your brain is going to be able to use those ketone bodies as a

fuel source now there are diets out there that limit your carbohydrate

consumption and you depend highly on eating fats now this could be dangerous

because too many ketone bodies in your bloodstream because now you're eating

too much fat and you're breaking that fat into fatty acids which will convert

into ketone bodies those ketone bodies can start making your blood highly

acidic which is dangerous and that would be known as ketoacidosis state some

cells in our body such as our adipose cells and our skeletal muscles

especially when they are in a relaxed mode or resting mode they need insulin

to help them absorb glucose without insulin those cells are not going to be

able to absorb the glucose out of our blood plasma if we look at this image

right here when we are in a fasting state we know that when we are fasting

our glucose levels are pretty low and so if our glucose levels are pretty low

then insulin is not going to be released and so if insulin is not going to be

released no way would those glucose molecules be able

to enter into the cell and so they will stay outside of the cell now what

happens is when we go ahead and we eat our glucose

levels are going to increase but for those glucose molecules to actually

enter into the cell insulin is required so when your glucose

levels increase in your blood plasma insulin is going to be released by the

pancreas once insulin is released by the pancreas it's going to go ahead and bind

to a specific receptor on the cell surface once it binds to that specific

receptor a bunch of cascade events will go ahead and take place causing those

vesicles inside of the cell carrying a bunch of glucose transporters known as

the glut 4 transporters those vesicles are going to get close to the plasma

membrane and via the process of exocytosis those vesicles are going to

release those glut4 transporters on the surface of the cell

once those glut 4 transporters are inserted on the surface of the cell

glucose is going to pass through those glut transporters into the cell and

therefore the glucose will only be allowed to enter into the cell only

after insulin binds to that specific receptor on the cell surface other cells

don't need insulin for glucose to enter into the cell and we're going to go

ahead and take a look at an example liver cells have glut 2 transporters

that are found always on their cell surface when we are fasting and our

glucose levels are pretty low we are definitely not going to be producing

insulin instead do we are going to be producing glucagon and glucagon

is going to help convert the glycogen storage that we have into glucose and so

what's going to happen is that the level of glucose inside of your liver cells

are going to be much higher compared to the level of glucose outside and so

those glucose molecules are actually going to make their way out through the glut 2

transporters out of the liver cell so that they can transport the

glucose outside of the liver cell to try to increase the glucose levels in your

blood plasma now after we eat a meal and our glucose levels increase that high

level of glucose is going to stimulate the production of insulin once insulin

is released it's going to bind to receptors found on the liver cells

causing the glucose to actually start entering into the liver cell via the

glut 2 transporter and once the glucose enters into the cell it's going to be

converted into the glucose 6-phosphate which is going to be used up in our

aerobic cellular respiration process and we're going to start making ATP and

actually by converting the glucose into glucose 6-phosphate that's always going

to keep the free glucose concentration low inside of our cell compared to

outside so more glucose keeps entering into the cell glucagon is produced by

our alpha cells within our pancreas what stimulates the production of glucagon is

low plasma glucose levels because we know that glucagon tries to increase the

glucose levels in our blood plasma so low levels of plasma

glucose can stimulate the production of glucagon another thing that can

stimulate the production of glucagon is when you have too much plasma amino

acids once glucagon is produced we know that

glucagon is going to go to the glycogen storage in your liver and in your

skeletal muscles and it's going to try to break down the glycogen into glucose

and so glucagon is going to definitely increase the process of glycogenolysis

the process of breaking down glycogen into glucose to try to increase your

glucose levels another thing is that when your plasma glucose levels are

pretty low your insulin your beta cells within your pancreas they're going to be

inhibited from producing insulin and so you're not going to be producing insulin

if your blood glucose levels are pretty low so what's going to happen is

that your body to try to make up for that lost or for that low levels of

glucose your body can also take the amino acids and the fatty acids in your

body and try to convert amino acids into glucose via the process known as

gluconeogenesis and your body is going to take the fatty acids and convert them

into ketone bodies so that your brain can go ahead and use those ketone bodies

and definitely if you are in a state of hypoglycemia - hyp meaning low glycemia

meaning sugar so if your sugar level is pretty low then your brain is going to

rely on the ketone bodies

also right here this image shows a negative feedback loop the once your

glucose levels increase then you're going to send a negative feedback signal

to stop your alpha cells from producing any more glucagon

The Description of Metabolism