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Hi. It's Mr. Andersen and in this podcast I'm going to talk about lipids
or the fats. The fat that's found in butter or the fat that's found in olive oil is what
we call a triglyceride. It's basically going to have a head, a glycerol head and then it'g
going to have three fatty acids tails. And that's where the energy is. And so when we
eat fat we can break it down. We have enzymes called lipases that are able to break that
down and then we can get energy from it. And that's been very important. We can store energy
in fats inside our body and then we can burn them when we need them. But don't forget that
fats in addition to providing energy also provide the surroundings. And so the cell
membrane that goes around every cell is made up of phospholipids. And the cholesterol is
found within the phospholipid by layer and that maintains the fluidity of the cell. And
so lipids are incredibly important. But where does the energy come from? That comes from
the hydrocarbons. And so if you look at those fatty acid tails it's essentially a carbon
attached to a carbon to a carbon to a carbon to a carbon . . . and then it has hydrogen
around the outside of it. And so we call that a hydrocarbon. And there's energy in those
bonds. And so gasoline burning out of control or the paraffin wax that's burning in a candle
is a hydrocarbon. There's a lot of energy between those carbon hydrogen bonds. And so
there's also a lot of energy found in butter or in olive oil. It's in the bonds between
the carbon and the hydrogen. And so let's start with a triglyceride. So this is a basic
fat. The head up here is going to be called the glycerol head and then this is going to
be the fatty acid tails that go down the end. And so fatty acid tail has so much carbon
and hydrogen in it that on this diagram we don't even draw them. Each of these points
represents a carbon, a carbon, a carbon. And then right here we're going to have two hydrogen
bonds or two hydrogens bonded to each of those carbons. And so you can see that there's a
huge amount of energy locked within that triglyceride and we can get that out through cellular respiration.
But know this. Those tails can come in two different forms. We can have what are called
saturated tails. A saturated tail is going to have hydrogen all the way around the outside.
And if you have hydrogen all the way around the outside then you're going to be saturated
with hydrogen. And if you're a saturated fat you're going to be a straight fat. And so
a triglyceride is going to have three of these fatty acid tails and the glycerol head, but
if it is saturated all of those are going to be straight. And if they're all straight
they can pack up on top of other triglycerides. And so saturated fats are normally going to
be a solid at room temperature. What happens if you don't have hydrogen all the way around
the outside? You're going to form these double bonds in here. If you have double bonds basically
what that does is it puts a bend in your tail. And so you're going to have a kinky tail.
And so if you're a saturated fat, you're going to look like this. If you're an unsaturated
fat you're going to look like this with kinky tails. And the kinky tails can't quite pack
together. And so normally fats that are unsaturated are going to be a liquid at room temperature.
Now humans have figured out how to take, for example, vegetable oil, which is a unsaturated
fat or it's going to be a liquid at room temperature and we can bubble hydrogen through it. We
can straighten out those tails and we can make a saturated fat called margarine that's
going to be a solid at room temperature. We've transformed this fat and if you know anything
about fats those saturated fats are the ones that are least best for us and can lead to
arteriolosclerosis, especially trans fats. Example then of how we've tried to get around
this. And this is a somewhat funny story. This is olestra. Olestra is a fat that was
made by humans. And so basically what they did us took a normal triglyceride but they
built it around a sucrose, so they built it around a sugar. And so instead of having just
three of these fatty acid tails they had sometimes eight, sometimes ten. Sometimes even more.
What's neat about that is that when you go through your digestive system we don't have
olestrase. We don't have an enzyme that can break that down and so the olestra moves right
through our digestive system. So it's a fat that feels like a fat, tastes like a fat but
it doesn't make us fat. And so Wow chips were introduced I think in the 1990s and had this
olestra in it. Basically what happened is when people started eating these Wow chips,
they got incredibly sick. They got cramping and they had to put a warning label on the
outside that it can lead to loose stools, and it pulls vitamins outside of your body.
They've kind of refined this since then and so there's not a lot of these adverse reactions.
I think Pringles light chips still contain olestra in it, but we're tricking our body,
because our body doesn't have those enzymes. Now I also said there are two more important
lipids. The first one's called phospholipids. Phospholipids are going to have, you can see,
two fatty acid tails, but they're going to have a head that contains a phosphate group.
That phosphate group is going to have a negative charge. And so normally if we were to pour
oil into water it's going to separate. And the reason why is that fats are non polar.
They don't have a charge. But what's neat about phospholipids is that they have a head
that is going to have a negative charge and then they have the tails that are uncharged.
And so if you just throw a bunch of phospholipids in water they'll form these spheres, micelles,
or they'll form these spontaneous membranes. And so the cell membranes of all cells are
made up of phospholipids. And so bacteria, archaea, eukarya, plants, animals, fungi,
we all have cell membranes. And those membranes are made up of phospholipids. They regulate
what gets in and out a cell. Cholesterol is going to maintain the fluidity of the membrane.
And so this cell membrane right here is made up of phospholipids. Those phospholipids are
constantly moving back and forth and that's important because it allows things like oxygen
to get in and carbon dioxide to get out. But if the cell gets heated up those phospholipids
tend to fall apart. And if it get's really cold they'll crowd together and so the function
of cholesterol is to grab onto those fatty acid tails and hold them together when it
gets too cold but keep them apart . . . or hold them together when they get to warm and
keep them apart when they get too cold. And so cholesterol is important at maintaining
that integrity of the cell membrane. And you can see cholesterol in this diagram right
here. We can build it in each of our cells and we have to build it in our cells, but
we have to get a little bit of it in our diet. And so we need lipids in our diet. If we don't
have lipids we can't get energy and more importantly we can't make our cell membranes. However,
today everybody's getting the fat they need. This is my favorite place to eat when I go
to California because we don't have them in Montana. This is In-N-Out burger. I love the
taste of a big burger from In-N-Out. The lipids are great but there's probably too much trans
fats in there. It's not good for me and could lead to heart disease. But for now I'm going
to keep eating them. So that's lipids, that's fat and I hope that was helpful.
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安德森's生物學:脂質 (Lipids)

5883 分類 收藏
Cheng-Hong Liu 發佈於 2015 年 2 月 14 日
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