Light Dependent Stage of Photosynthesis: Where everything goes
Summary
TLDR视频脚本详细解释了光合作用中依赖光阶段的电子、氢和氧等元素的去向。在叶绿体的类囊体膜上,光系统1和光系统2作为蛋白质复合体,含有叶绿素,吸收阳光能量。阳光激发光系统中的电子,使它们成为高能电子,这些电子通过一系列分子传递,最终用于合成NADPH。同时,光系统2通过分解水分子补充失去的电子,释放氧气。此外,通过电子传递过程中的能量损失,建立了跨膜的氢离子梯度,进而通过ATP合酶生成ATP。整个过程中,产生了NADPH和ATP,为光合作用的非依赖光阶段提供能量和还原力。
Takeaways
- 🌿 **光合作用分为两个阶段**:光依赖阶段和光独立阶段,视频中主要讲解光依赖阶段。
- 🏞️ **光依赖阶段发生位置**:在叶绿体的类囊体膜上。
- 🔵 **类囊体膜的结构**:含有多种蛋白质复合体和分子,被类囊体腔和基质包围。
- ☀️ **光系统的作用**:光系统1和光系统2是蛋白质复合体,含有吸收太阳能量的叶绿素。
- 🚀 **电子激发和传递**:阳光激发光系统中的电子,使其具有更高能量,并在分子间传递。
- 💧 **水的光解作用**:光系统2通过水的光解补充失去的电子。
- 🚨 **氢离子梯度的建立**:电子传递过程中,氢离子被泵入类囊体腔,形成氢离子梯度。
- 🔋 **ATP的合成**:氢离子通过ATP合酶的协助扩散,驱动ATP的合成。
- 🍀 **NADPH的生成**:高能电子与NADP+结合,形成NADPH,用于光合作用的光独立阶段。
- 🔵 **氧气的释放**:水分子的光解过程中产生氧气,作为副产品释放。
- 🔄 **光依赖阶段的输出**:产生ATP、NADPH和氧气,为光合作用的光独立阶段提供能量和还原力。
Q & A
光合作用中的光依赖阶段发生在哪里?
-光合作用的光依赖阶段发生在叶绿体内的类囊体膜上。
类囊体膜被什么包围?
-类囊体膜被一种称为基质的流体基质所包围。
光系统1和光系统2是什么?
-光系统1和光系统2是蛋白质复合体,含有叶绿素,能够吸收阳光中的能量。
当阳光照射到光系统2时,会发生什么?
-阳光照射到光系统2时,叶绿素吸收能量,激发其中的两个电子,使它们成为高能电子。
光系统2失去电子后,如何补充电子?
-光系统2通过分解水分子,从水中获取电子来补充失去的电子。
电子在光系统2中激发后,它们是如何传递的?
-激发后的电子会从一个分子传递到另一个分子,最终离开光系统2,进入一个叫做质体醌的较小分子。
ATP合酶是什么?
-ATP合酶是一种蛋白质,当氢离子通过它进行协助扩散回到基质时,会导致ATP合酶的一部分旋转,从而帮助合成ATP。
光依赖阶段中,氢离子浓度梯度是如何形成的?
-通过细胞色素b6f复合体将电子传递给质体蓝素的同时,将两个氢离子从基质泵送到类囊体腔中,形成了氢离子浓度梯度。
光依赖阶段产生了哪些能量丰富的分子?
-光依赖阶段产生了ATP和NADPH这两种能量丰富的分子。
光合作用中产生的氧气来自哪里?
-光合作用中产生的氧气来自于水分子的分解。
光依赖阶段产生的ATP和NADPH在光合作用的下一阶段中起什么作用?
-光依赖阶段产生的ATP和NADPH在光合作用的光独立阶段中使用,用于固定二氧化碳。
为什么氢离子不能直接穿过磷脂双层?
-由于磷脂双层中的脂肪酸尾部是非极性的,它们会排斥带电的粒子,如氢离子,因此氢离子不能直接穿过磷脂双层。
Outlines
🌿 光合作用光依赖阶段的电子传递
本段视频主要解释了光合作用中光依赖阶段的电子传递过程。光依赖阶段发生在叶绿体的类囊体膜上,涉及到光系统1和光系统2,这两个光系统是蛋白质复合体,含有吸收太阳光能的叶绿素。当阳光照射到光系统2时,叶绿素吸收能量使电子激发,然后这些高能电子离开光系统2,通过一系列分子传递,最终用于合成NADPH。同时,水分子被分解,提供电子以补充光系统2失去的电子。此外,还涉及到质子泵的作用,通过质子梯度产生ATP。
🔋 光依赖阶段的能量转换与ATP生成
在光合作用的光依赖阶段,除了产生NADPH外,还建立了跨膜的氢离子梯度,导致类囊体空间内氢离子浓度高,基质中氢离子浓度低。氢离子通过ATP合酶进行协助扩散回到基质,此过程中ATP合酶部分旋转,将磷酸基团加到ADP上形成ATP。通过12个水分子的光解过程,最终产生18个ATP分子。同时,还生成了12个NADPH分子和6个氧分子。视频中还解释了氢离子数量的计算,说明了在光依赖阶段结束时,只有12个氢离子被输出。
Mindmap
Keywords
💡光合作用
💡光依赖阶段
💡叶绿体
💡类囊体膜
💡光系统
💡电子传递链
💡ATP合酶
💡NADPH
💡质子梯度
💡氧气
💡水分子光解
Highlights
光合作用中的光依赖阶段发生在叶绿体的类囊体膜上
类囊体膜被类囊体基质(stroma)所包围
光系统1和光系统2是光依赖阶段中最重要的分子,它们是蛋白质复合体并含有叶绿素
阳光照射到光系统2时,叶绿素吸收能量激发电子
激发的电子通过一系列分子传递,最终到达光系统1
光系统2通过分解水分子来补充失去的电子
水分解过程中释放的电子和质子对光合作用至关重要
细胞色素b6/f复合体利用电子流动的能量将质子泵入类囊体空间
电子最终传递给铁硫蛋白,然后用于合成NADPH
NADPH是高能分子,用于光合作用的光独立阶段
通过建立跨膜的质子梯度,质子通过ATP合酶返回基质,驱动ATP的合成
ATP合酶的旋转驱动ADP与磷酸结合形成ATP
光依赖阶段的输出包括18个ATP分子和12个NADPH分子
同时,光合作用还会产生6个氧气分子作为副产品
光依赖阶段结束后,会生成12个氢离子
NADPH的生成涉及到从基质中借用的氢原子的回收
通过计算12个水分子的分解,可以解释光依赖阶段中氢离子的数量
视频详细解释了光合作用中电子和氢离子的流动路径
光依赖阶段的详细解释有助于理解光合作用的复杂机制
Transcripts
if you're wanting to understand where
all the electrons and hydrogens and
oxygens and everything go in the light
dependent stage of photosynthesis then
you've come to the right place because
that's what i'm going to explain in this
short video i'm assuming that if you're
watching this video you already know the
overall equation for photosynthesis you
already know it happens in two different
stages that we call the light dependent
stage and the light independent stage
but as i said in this video we're just
focusing on the light dependent stage
the light dependent stage of
photosynthesis takes place within a
chloroplast on the membranes of
thylakoids and just notice that those
thylakoids are surrounded by a fluid
matrix called stroma
that's what we're looking at here you
can see across the middle of the screen
is a thylakoid membrane at the bottom of
the screen we're looking at the inside
of a thylakoid disc at the thylakoid
space and at the top of the screen we're
looking at the stroma notice that the
thylakoid membrane has a whole lot of
proteins protein complexes and other
molecules we'll look at each of those in
turn
and notice also that there is water down
in the lower left hand corner of the
screen and three hydrogen ions in the
stroma just above the membrane it's
important to notice those because they
help you to sort of add everything
together and see where everything goes
there are three hydrogen ions there in
the stroma already to begin with
by far the most important molecules here
are photosystem 1 and photosystem 2.
both of those photosystems are a
collection of proteins they're a protein
complex and they contain chlorophyll
that pigment that absorbs the energy out
of sunlight notice that they also have
a couple of electrons as well both
photosystems have some electrons in them
two electrons in there
when sunlight hits photosystem two that
energy is absorbed by chlorophyll and
used to excite the two electrons that
are in photosystem two so those
electrons become higher energy electrons
they absorb that energy and become
excited and in that excited state you
know they have a tendency to lose energy
and go back from being excited to being
less excited and they do that by being
passed from one molecule to another they
leave photosystem two and move into a
smaller molecule called pq or
plastoquinine
but notice at this point that
photosystem 2 has lost its electrons and
remember we said photosystem 2 has to
have a couple of electrons so it needs
to replace them and where do you think
it gets those from well that's where
water comes into things because water is
a really great source of electrons each
of the hydrogens in water is sharing an
electron with oxygen so what photosystem
2 does is it breaks the hydrogens off
the oxygen
and the electrons that were being shared
by the hydrogens with the oxygen and
then released and they go into
photosystem two replacing the electrons
that it now lost to plastoquinine all
right so back to plastoquinone it passes
its electrons to another protein called
cytochrome
and cytochrome as these electrons flow
through cytochrome losing energy as they
go that energy is used by cytochrome to
pump two hydrogen ions
across the membrane into the thylakoid
space the electrons in cytochrome then
get passed to another little molecule
called plastocyanin now at this point
let's look at photosystem
1. just like photosystem 2 photosystem 1
is able to absorb sunlight because it
contains chlorophyll and just like
photosystem 2 photosystem 1 also has 2
electrons in it and when it gets hit by
sunlight the energy from the sunlight is
again used to
to to excite those two electrons and
they get passed to a molecule called
ferrodoxin
but just like photosystem 2 photosystem
1 needs to replace those lost electrons
and it does that by grabbing the
electrons from plastocyanin and sitting
there right next to it so again
photosystem 1 is right back to where it
was before ready to go again but
ferrodoxin now has a couple of extra
electrons which it passes to an enzyme
called
nadp plus reductase now nadp plus
reductase is a water-soluble enzyme
there's nadp plus reductase floating
around in the stroma but it's also
sitting in the membrane of the thylakoid
as well it's in both places
in any case once it gets a couple of
high energy electrons those electrons
because the electrons of course are
negatively charged those electrons are
used to attract two positively charged
molecules namely nadp plus
and a hydrogen ion both of which are
electrically positive so now we've got
two positively charged molecules and two
negatively charged electrons the
electrons go into nadp plus and we say
reduce it
that is
the hydrogen gets added onto it and it
becomes nadp
a high energy molecule that is then used
in the light independent stage of
photosynthesis
okay so at this stage
what we've done is set up well firstly
we've created an nadph molecule but
secondly we've set up
a hydrogen ion gradient across the
membrane you'll notice there's now a
high concentration of hydrogen ions
inside the thylakoid space and a low
concentration of hydrogen hydrogen ions
in the stroma all things being equal
those hydrogens would diffuse back into
the stroma
down their concentration gradient and
down their electrical gradient too for
that matter but because they're
positively charged they're repelled
strongly by
the fatty acid tails of those
phospholipids phospholipids have two
fatty acid tails that are non-polar and
they'll repel anything that's got an
electrical charge on it like these
hydrogens so they can't diffuse across
the phospholipid bilayer so instead
they need to diffuse back into the
stroma by facilitated diffusion through
a protein called atp
synthase and as they move through atp
synthase
they actually cause part of atp synthase
to rotate and as it rotates it
physically grabs a phosphate ion and
joins it onto adp to form atp and from
doing that we get one and a half
atp molecules now you might be saying
well how do we get one and a half atp
molecules
well of course we don't really have one
and a half atp molecules because this
process doesn't start with one water
molecule it starts with 12 water
molecules so if we multiply 1.5 atps by
12 that gives us 18 atp molecules which
is the output the atp output of the
light dependent stage and while we're
multiplying things by 12 because we've
got 12 water molecules going in and not
just one
let's think about nadph
we don't just get one nadph of course we
get 12 nadph and again that's the nadph
output of the light dependent stage of
photosynthesis
let's think about oxygen
we don't just have one oxygen atom if we
have 12
water molecules and not just one then we
can multiply that by 12 as well and that
gives us 12 oxygen atoms or six oxygen
molecules each containing two oxygen
atoms
but what about these four hydrogen ions
up here because you might know that we
don't get
48 hydrogens if we multiply 4 by 12 we'd
have 48 hydrogens but we don't have 48
hydrogens coming out of the light
dependent stage we only have 12. so how
do we account for that
well firstly remember that
nadph was made by using a hydrogen that
was already in the stroma
so let's pay that hydrogen back so that
the light dependent stage is ready to go
again okay so we'll pay that hydrogen
back and remember early on in in the
process
that protein called
cytochrome pumped two hydrogens from the
stroma down into the thylakoid space so
if we pay those back as well that leaves
us with just
one
hydrogen
and that one hydrogen now of course if
we multiply that by 12
gives us 12 hydrogen ions which is the
hydrogen output of the light dependent
stage of photosynthesis
well i hope you found that really
helpful
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