YouTube Transcript:
Photosynthesis - Light Dependent Reactions and the Calvin Cycle

Skip watching entire videos - get the full transcript, search for keywords, and copy with one click.

Video Transcript

Available languages:

View:

in this video we're going to talk about

photosynthesis just a brief introduction

into it

now what is photosynthesis

let's think about the word photo and

synthesis photo means light

synthesis means to build something

and that's what we're doing we're using

the energy provided by light to build

something in this case carbohydrates

here we have the net equation for

photosynthesis we're combining six water

molecules with six carbon dioxide molecules

molecules

and using light

to build

simple sugars like glucose c6h1206

and we're also going to get oxygen gas

as a product as well

now on the left side of this equation

are the reactants

and on the right side are the products

the picture on the left tells you

where these molecules

enter and leave the plant water

water

enters the plant

through the roots

so the plant pulls up water and minerals

that it need

through the roots from the soil

carbon dioxide

enters the leaves of the plant through

tiny openings known as stomata

and oxygen

it leaves the plant

through those same openings

openings

so it's important to understand that

water and carbon dioxide they go into

the plant and the plant releases oxygen

during photosynthesis

now let's move on to the chloroplasts

the chloroplast is the organelle that

carries out photosynthesis

on the other hand the organelle that is

responsible for cellular respiration is

the mitochondria

now these two processes

they are exact opposites of each other photosynthesis

photosynthesis

converts carbon dioxide and water with

the help of light energy into glucose

and oxygen gas

on the other hand

cellular respiration takes glucose and

oxygen gas

and converts it back into carbon dioxide

and water releasing energy in the process

process

so you need to be familiar with these two

two processes

processes

now the pigment that is responsible for

absorbing light energy

is known as chlorophyll

and chlorophyll is found in the thylakoids

thylakoids

which you can see in this picture

one stack of thylakoids is known as the granum

granum

if you have multiple stacks

this is called grana

grana

so that's the plural form of the word granum

granum

the lumen is the fluid inside of the

thylakoid and the stroma

the chloroplast has two membranes the

inner membrane and the outer membrane

and between that you have the

intermembrane space

so make sure you understand that the

chloroplast is the organelle in which

photosynthesis is carried out

now you also need to know that

chlorophyll absorbs blue light

and it absorbs the red light however

it reflects green light this is why most

photosynthesis can be broken down into

two stages

the light dependent reactions

and the light independent reactions

the light dependent reactions

occur inside of the thylakoids within

the chloroplast

the light independent reactions

which is basically the calvin cycle also

known as the dark reactions

they occur

in the stroma

of the chloroplasts

now the reason why they're called light

independent or dark reactions is because

they can proceed without the assistance

of light energy

the light dependent reactions

oxidizes water

into oxygen gas

and remember oxidation involves the loss

of electrons

so whenever an oxidation reaction occurs

nad plus i said that wrong nadp plus rather

rather

picks up those electrons and is reduced

into nadph

now some of the energy that is

transferred by light

is used to

make atp

from adp and phosphate

atp is produced by chemiosmosis using an

enzyme called atp synthase

so for the light dependent reactions you

need to know that the products are

are

oxygen gas atp

and nadph

the reactants are water

nadp plus

now let's move on to the light

independent reactions or the calvin cycle

cycle

the calvin cycle takes in carbon dioxide

and reduces it into

into

sugars such as glucose

now because that's a reductive process

oxidation has to happen somewhere nadph

nadph

is oxidized

back into

so nadph it gives up its electrons

turning into nadp plus

carbon dioxide ultimately receives those

electrons and eventually turn it into glucose

atp

is used to power that process

as atp converts back into adp and p

it energizes the calvin cycle giving it

the energy it needs to convert co2 into glucose

glucose

so the reactants

of the calvin cycle are

carbon dioxide

atp and nadph

the products are

are

sugars such as glucose

nadp plus

adp and p

so let's begin our discussion now with

the light

dependent reactions

so what we have here is the electron

transport chain inside of the thylakoid membrane

now the first thing that's going to happen

happen

is a light particle will strike

photosystem 2

and it's going to excite the electrons

in chlorophyll so chlorophyll is going

to lose its electrons

which will flow into this mobile

electron carrier called plastoquinone

plastoquinone

now because chlorophyll lost electrons

it needs to replenish those lost electrons

electrons

and so it's going to take the electrons

from water

oxidizing it

into oxygen gas

so one water molecule

produces one oxygen atom

and it's going to give off two hydrogen ions

ions

and also two electrons

so water will ultimately lose two

electrons to photosystem two

photosystem two is also called 680 because

because

that's the wavelength of light that has

the highest absorption it's 680 nanometers

now plastoquinone is going to carry the electrons

electrons

to cytochrome b6f complex

and as the electrons pass through that complex

complex

what's going to happen next is

it's going to pump protons

from the stroma that is from outside of

the thylakoid

into the lumen or the inner thylakoid space

so the proton concentration in the stroma

stroma

is going to decrease

while the proton concentration

inside the thylakoid is going to increase

increase

producing a concentration gradient

now the electrons will continue the

journey from cytochrome b6f to

this particular peripheral protein plastocyanin

plastocyanin

this is a copper containing protein

and it's going to transfer the electrons

to photosystem one now

now

from this journey the electrons have

lost some of its energy

and so what's going to happen here is

the electrons

will gain more energy

by being struck by another photon of

light in photosystem one

also known as p700 so this particular

photosystem has its maximum absorption

at a wavelength of 700 nanometers

so after the electron

is struck by a photon of light

that photon will impart its energy to

the electron the electron will get excited

excited

and having more energy it's going to go to

another peripheral protein called

ferrodoxin which is an iron sulfur protein

protein

and that's going to carry the electrons

to nadp reductase now

now

napd reductase

it's a peripheral protein but it's also

an enzyme

you can see the word ace

this enzyme is going to reduce nadp plus

so the electrons

are going to leave

and they're going to

meet up with nadp plus

once nadp plus

accepts the electrons

along with a hydrogen ion

so this reaction also reduces

the hydrogen ion concentration inch in

the stroma which

which

will favor the production of atp soon

so because there's a buildup of hydrogen

ions on the inner thylakoid space

and there's

very little hydrogen ions in the stroma

what's going to happen here now is these

hydrogen ions

due to this concentration gradient

they will begin to flow through an

enzyme called atp synthase in the

process known as chemiosmosis

as those hydrogen excuse me as those

hydrogen ions flow through that enzyme

this protein will rotate in such a way

that it's going to combine adp and

phosphate to make atp

so that's how the electron transport

chain works

in photosynthesis

so as we can see here water is oxidized

into oxygen gas

nadp reductase produces

produces

the electron carrier nadph

and atp synthase is used to produce atp

so those are the major products of the

light dependent reaction and keep in

mind that photosystem 2 not photosystem

1 but photosystem two is what

converts water into oxygen gas you might

be tested on that

now let's talk about the other part of

photosynthesis that is the calvin cycle

or the light independent reactions

the calvin cycle can be broken down into

three parts

the first part is the fixation of carbon dioxide

dioxide

the second part is reduction and the

third part is the regeneration of rubp

so the first thing that happens is that

carbon dioxide enters the cycle

carbon dioxide is going to react with

ribulose biphosphate

catalyzed by the enzyme rubisco

and that's going to turn into

3-phosphoglycerate represented by the

symbol pga

so that's carbon fixation rubp

rubp

is a molecule with five carbon atoms

on carbon 1

we have a phosphate group and on carbon

5 we have another phosphate group so

that's rubp

now there's three of them and they're

going to react with three co2 molecules

now when one molecule of co2 reacts with

one molecule of rubp

we're going to get initially a6

carbon molecule but that's going to be

broken up into two

so pga is a three carbon molecule

and it's going to have one phosphate group

group

so if we keep track of a total number of carbons

carbons

if each rubp has five carbons three of

them has 15 carbons

and then we're going to add three

carbons from the three co2 molecules

so we should have a total of 18 carbons

so thus there's six

now

the enzyme kinase when you see that that

enzyme is used to transfer a phosphate group

group

to a molecule

and so this next step requires atp

to phosphorylate three phosphoglycerate

and so now we have one three by phosphoglycerate

so we still have a three carbon molecule

but now we have a phosphate group on

carbon one

and carbon three

so as we could see here pga kinase is an

enzyme that catalyzes the conversion of

3-phosphoglycerate into 1-3 by phosphoglycerate

phosphoglycerate

so atp

gives up a phosphate in order to become adp

adp

and that phosphate is transferred to

this molecule as you can see we now have

two phosphate groups so anytime you see

a kinase enzyme it catalyzes the

transfer of a phosphate group from one

now in the next step

we are going to use nadph

we're going to use this molecule to

reduce 1 3 by phosphoglycerate into g3p

glyceraldehyde 3-phosphate

so nadph is going to convert into nadp plus

now we need six

molecules of nadph to do this

this reaction will be catalyzed by the

g3p dehydrogenase enzyme

this enzyme

as it suggests the words dehydrogenase

now at this point we're going to get six

g3p molecules one

one

of the six g3p molecules is going to be

used to produce sugars like glucose and

fructose and things like that

the other five g3p molecules

is used to regenerate the three

ribulose biphosphate molecules

so keep in mind the total number of

carbons here is 15.

has three carbon atoms

and it has a phosphate group on carbon 3.

so 5 times 3 gives us a total of 15

carbons which is what

we started with

so notice the net result

the calvin cycle converts three

molecules of co2

into one molecule of g3p

and that is the net result of the carbon cycle

now let's summarize what we've just considered

considered

in the calvin cycle we saw that three

molecules of co2 was converted into one

molecule of g3p

and that required

and six

six

now in order to make one molecule of glucose

glucose

we're going to need six molecules of co2

and once that enters into the carbon

cycle that's going to produce two

molecules of g3p

which can be used to produce one

and so we need to double the numbers

that's going to require

and 12 molecules

of nadph

and so that's a simplified review of photosynthesis

photosynthesis

and the two process

the two processes rather that make it up

that is the light dependent reactions

which occur

inside of the thylakoid membrane and the

light independent reactions or the

calvin cycle which occurs in the stroma

of the chloropaths so keep that in mind

and that's it for this video thanks

again for watching and don't forget to subscribe

Click on any text or timestamp to jump to that moment in the video

Most transcripts ready in under 5 seconds

One-Click Copy125+ LanguagesSearch ContentJump to Timestamps

Paste YouTube URL

Enter any YouTube video link to get the full transcript

Most transcripts ready in under 5 seconds

Get Our Chrome Extension

Get transcripts instantly without leaving YouTube. Install our Chrome extension for one-click access to any video's transcript directly on the watch page.

Add to Chrome — Free

Works with YouTube, Coursera, Udemy and more educational platforms

Get Instant Transcripts: Just Edit the Domain in Your Address Bar!

YouTube

←

→

↻

https://www.youtube.com/watch?v=UF8uR6Z6KLc

YoutubeToText

←

→

↻

https://youtubetotext.net/watch?v=UF8uR6Z6KLc

YouTube Transcript:Photosynthesis - Light Dependent Reactions and the Calvin Cycle

Video Transcript

Paste YouTube URL

Transcript Extraction Form

Get Our Chrome Extension

Get Instant Transcripts: Just Edit the Domain in Your Address Bar!

YouTube Transcript:
Photosynthesis - Light Dependent Reactions and the Calvin Cycle