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hi guys in this video we'll have an

0:04
introduction to carbohydrates we'll look
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at monosaccharides glucose isomers of
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glucose ribose and then we'll finish
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with a summary
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so carbohydrates are an important family
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of molecules particularly biological
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molecules found in all organisms
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and we describe them as organic
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molecules and organic molecules remember
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means that they contain carbon
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and they have a variety of important
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roles in the cell one of their most
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influential roles is as a source of
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energy and a store of energy as well
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so obviously all cells need the ability
0:36
to produce energy to carry out various
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processes
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and sugars are one of the foods that we
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eat to gather most of our energy and
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carbohydrates can be termed as sugars as
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well
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so we can find sugars in foods for
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example pasta we also find it in rice
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and bread as well and there's lots and
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lots of different sources of different
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types of carbohydrates
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they also have a structural role in
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particular cells as well so here we have
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a plant cell
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and plant cells all have a feature
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around their perimeter known as the cell
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wall
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and this cell wall structure adds
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strength and rigidity to the cell and
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this kind of property allows plants to
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stand upright and grow very tall
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a carbohydrate molecule whichever type
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it is contains only three elements and
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they are carbon hydrogen and oxygen so
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here we have an example of a
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carbohydrate
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don't worry too much about this
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particular example but it is
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glyceraldehyde and you can see it
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consists of only three elements we have
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carbon atoms hydrogens scattered around
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and various oxygens too but there's no
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additional element in this structure and
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if you want to help remember which
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elements are in carbohydrates you may
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need to look at the we have carbo for
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carbon
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hydra for hydrogen and eight for oxygen
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because eight usually refer to the
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addition of oxygen
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so any example of a carbohydrate you
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come across whether they be very small
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or very large will only ever contain
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carbon oxygen and hydrogen
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so now let's talk about a type of
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carbohydrate known as a monosaccharide
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so the simplest carbohydrates are called
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monosaccharides and they're basically
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the monomers or building blocks for more
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of the complex carbohydrates
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so remember when we talk about
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biological molecules we have individual
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units known as monomers
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and we have monomers joined together
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into chains and these become polymers
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in this case one of these units for a
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carbohydrate is known as a
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monosaccharide with saccharide referring
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to sugar and the mono referring to one
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and many of these can join up to form
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more complex carbohydrates in exactly
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the same way
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so if we form two monosaccharides and
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form a bond between them
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we then form a disaccharide so the only
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thing that changes is the idea that
2:47
we've gone from mono which means one to
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die which means two
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so here we have two individual
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monosaccharides
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and in forming a bond between them we
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have two monomers joined together which
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is now known as a disaccharide
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and if we were to add many many more
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monosaccharides into a chain we end up
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with more than two three four we end up
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joining up to make a polysaccharide
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where poly as in the case with any
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biological molecule means many so this
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is the polymer of a carbohydrate so if
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we had four monosaccharides joined
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together each of them get their own bond
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between each monosaccharide and we end
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up with a polysaccharide so it's
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basically just changing the prefixes of
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the words
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monosaccharides have particular
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properties as these individual units
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they're soluble so they can dissolve
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and they're sweet tasting carbohydrates
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so they're also known commonly as sugars
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so by definition monosaccharides are
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single sugar monomers they are the
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simplest carbohydrates you cannot get
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smaller carbohydrates than these
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and they have their own general formula
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as well not to be confused with the
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general formula of general carbohydrates
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the general formula of a monosaccharide
3:59
is c h2o so those three elements again
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and then we put this all in brackets and
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we put n underneath so this formula is
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basically saying that you have a certain
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number of carbon atoms and a certain
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number of oxygen atoms but twice the
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number of hydrogen atoms
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so if you had a monosaccharide with
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three you'd have n is three three
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carbons three oxygens and six hydrogens
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so this is the general formula for any
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of those monosaccharide single units
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so bearing this formula in mind the
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molecular formula for each type of sugar
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or each type of monosaccharide can be
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worked out just by using the formula
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so we find the molecular formula which
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is the actual number of atoms in the
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sugar using the general formula which is
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to be applied to any of them
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so let's just go through each sugar
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where we've got three carbon atoms four
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carbon atoms
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five and six so the general formula is c
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h2o n
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so if we had three carbons we would have
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c is three
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h2 so that's two times three which is
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six
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and then o is the same as the carbon and
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then if we had four we would have c4
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h is always double this so h8
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and then we would have o4 again so you
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can see the pattern for monosaccharides
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is there's always the same number of
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carbons and oxygens but the hydrogens
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are double
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for the five carbon one we would have c5
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h10
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o5 and 6 would be c6h12o6
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so what we've got is we've got different
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types of monosaccharides with different
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numbers of carbons
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and what you can have is you can have a
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specific name for the sugar like
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glyceraldehyde 3os ribose
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but you can also have a general term for
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any sugar with a certain number of
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carbons
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so a monosaccharide that ever has three
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carbons is known as a triose so you'll
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find that sugars tend to end in o's just
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like glucose or fructose
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trios is a general term for any sugar
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with three carbons and then a full
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carbon one would be a tetros
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just like tetrahedron has four sides so
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tetra refers to any sugar with four
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carbons like this one pentose for five
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and hexose for six
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and what we've got in this table are a
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few examples so a trio sugar has three
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carbons and if it's a monosaccharide it
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has three six and three an example of
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this is glyceraldehyde
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so each of these red dots is a carbon
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and you can see there are three of them
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each of those would be bound to various
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hydrogens and so you can count the
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hydrogens there are six of them and then
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you can count the oxygens at which there
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will be three an example of a tetros is
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known as threos
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pentose is known as ribose which we'll
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talk about in another slide and the hexo
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is probably the most common glucose
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you've heard of is glucose so for any
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sugar that you're given you can work out
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its molecular formula based on the
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general formula and therefore it's a
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type of sugar known as either trios if
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it's three tetros if it's four etc
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there's one hexose that we've mentioned
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here which is glucose but there are two
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other commonly found hexose
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monosaccharides which you may have heard
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of known as fructose and galactose so
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remember they're both still
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monosaccharides so single unit
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carbohydrates but they're both hexoses
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so we've got fructose and galactose
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and they're both hexose monosaccharides
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which means they have six carbons in
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their ring and so they're classed within
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this family so there's a lot of levels
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here but think about hexose etc refers
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to how many carbons monosaccharides are
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the individual units of any carbohydrate
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and then carbohydrate is the whole
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family so just think of it in different
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layers glucose is one of the most heard
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of examples of a sugar and it is a
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monosaccharide and we describe it as a
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hexose sugar because it has six carbons
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so if we were to look at the molecule
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here we can see we've got one
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two
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three four five six carbons
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it doesn't matter what shape it is if it
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ever has six carbons
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it's automatically classed as a hexose
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hence hexagon six sites so it doesn't
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matter where the carbons are in any
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monosaccharide however many carbons it
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is dictates what type of sugar it is and
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remember we can work out the molecular
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formula using the general formula for a
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monosaccharide which is ch2on
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so if we know it as a hexose we've got
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six carbons which means there are h2n so
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12 hydrogens and the same number of
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oxygens which is six so the molecular
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formula for glucose is c6h12o6
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glucose is a really important sugar and
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it pops up in lots of aspects of biology
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it's the main source of energy in
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respiration for any cells
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so
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glucose molecules are combined with the
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oxygen that we breathe in from the air
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and it reacts to give two side products
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and one useful product so it gives co2
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and water which are both not really used
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much
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and then it's also used to produce an
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important molecule known as atp
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and it's from this atp that we get our
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energy so glucose is important to carry
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out respiration and this whole process
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of making atp is what we call
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respiration
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it's not only used as energy but
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remember we said carbohydrates are used
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in a structural world too
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it's the building block for larger
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carbohydrates
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so in this long chain here we have a
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polysaccharide
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and the monosaccharides in this case are
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glucose and when we have a
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polysaccharide of glucose arranged in
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this spiral structure we have a
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particular molecule known as amylose
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which is part of starch so it's a
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building block for larger molecules
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so in order to be suited for these
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properties glucose is well adapted it
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has particular features in its molecule
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that make it good as an energy source
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and to be able to build up into building
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blocks so first of all it's a very small
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monosaccharide so it's easily
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transported in and out of cells and it's
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done so through carrier proteins so here
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we have the cell membrane and let's say
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that this is outside of the cell and
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this is inside of the cell specific
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proteins that are embedded into the cell
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membrane are called carrier proteins and
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they're a type of protein in the cell
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membrane and they can help take this
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glucose and transport it across the
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membrane into the cell so this is useful
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if we want to take up glucose to carry
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out respiration and because it's small
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it's able to fit inside these carrier
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proteins quite easily the carrier
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proteins change their shape in order to
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transport the glucose from one side to
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the other
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it's also a very soluble molecule
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because of its size so because of this
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it's easily transported around an
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organism for example for us it can
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travel in the bloodstream
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without any extra help other than being
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dissolved in water
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it's not very reactive compared to some
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other monosaccharides so the breakdown
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in respiration must be catalyzed and
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controlled by enzymes
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so even though less reactive is normally
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a hard thing to get over
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if the glucose can only react when it
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enters the enzyme the enzymes can
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control how often this happens
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so enzymes control the rate of
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respiration which is really important if
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we respire too much or too little this
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can be a problem and therefore because
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they're catalyzed by enzymes they're
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able to control this
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glucose also exists in what we call
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isomers
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so glucose itself doesn't always exist
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exactly in the same way it has different
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structural forms known as isomers
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so in chemistry an isomer is basically a
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molecule or molecules which have the
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same chemical formula but they have a
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different arrangement of their atoms in
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space
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so there are lots of examples of this
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but if we take it in simple terms
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if we had a carbon-carbon double bond
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here and we've got two molecules which
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look very much the same what we've got
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is we've got greens both facing upwards
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on this molecule but on this molecule
11:45
we've got one facing upwards and then
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one on this side so overall they have
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the same chemical formula
11:52
i.e they contain the same number of
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atoms the same groups the same number of
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bonds and everything basically is the
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same identically
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but they have different arrangement of
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atoms because now the green and the
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yellow have swapped over
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so different arrangement and you might
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be asking well why doesn't the green and
12:09
yellow just swap around and usually it
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would but because of the double bond
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it's restricted from doing this
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so this only really happens in molecules
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where there's some sort of physical
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block to them just swapping over again
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the double bond in the carbon means that
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these two won't ever swap over again
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and in some sugars like glucose we have
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the similar kind of structures stopping
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this rotation and the number of isomers
12:31
that something has is basically the
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number of different arrangements that it
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can exist in
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so glucose itself has two isomers
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one of them is called alpha glucose and
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the other is called beta glucose and
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they differ by one single position of a
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hydroxyl group or an oh group
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so let's look at glucose and its two
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isomers here on the left side we have
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alpha glucose and on the right side we
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have beta glucose
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they look very much the same but the
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only difference is that on this carbon
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here the one on the right side on alpha
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the oh is on the bottom and on beta the
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oh is on the top so it's these two
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groups that swap around on the carbon
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and they can't just swap back easily
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because of these other bonds remember
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carbon bonds to four things
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so because of this strict rotation
13:19
they're not allowed to just change
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between them so they're exactly the same
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molecules six carbons and all the other
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groups are exactly the same
13:27
but the difference is alpha the oh is on
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the bottom
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and the oh is on the top
13:32
you need to know which is which and
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sometimes the best way to remember is
13:35
that if you think alpha is that where
13:38
the ohs are on the same side
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on the beta they're on different sides
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whatever works for you
13:44
and obviously that means that when we
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choose either alpha or bc glucose to
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build up things i.e different
13:50
polysaccharides
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they have different properties
13:53
so we can make different polysaccharides
13:55
depending on whether we choose to make
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them out of alpha glucose or whether we
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choose to make them out of beta glucose
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as they're building blocks so remember
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we said earlier that some
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polysaccharides can have alpha glucose
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as a monosaccharide and in this case we
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would have amylose
14:09
but in other polysaccharides we have the
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monomer of beta glucose
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and an example of a polysaccharide where
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this occurs is known as cellulose which
14:18
is found in plant cell walls so
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depending on what the monomer is the
14:21
polymer can be very different another
14:23
important example of a sugar is ribose
14:26
ribose is a pentose because it has five
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carbon atoms and it's still a
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monosaccharide
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so pentose refers to five carbons and we
14:35
can work out the molecular formula for
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this as it's a pentose sugar because
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it's c5 twice the number of hydrogens
14:42
and then five oxygen so c5h10o5
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and if you were to count all of these up
14:47
you'd find that's what it is so this is
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what ribose looks like it's got a
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pentagonal shape and it happens to have
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five carbons anyway sometimes the
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carbons don't always make the corners of
14:57
the shape one of the corners is actually
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made by oxygen and this was the case in
15:00
glucose as well
15:02
where do we find ribose well they're
15:04
important in biology because they're
15:05
found in a lot of important molecules
15:07
such as rna or ribonucleic acid which is
15:10
one of those nucleic acids used in
15:12
transcription
15:14
and also found in atp2 so rna
15:17
is a
15:19
polynucleotide and this is the ribose
15:21
and you can see there's repeating
15:22
nucleotides all in a chain and also in
15:25
the molecule atp we have a sugar ribose
15:28
making up the main building block of the
15:30
molecule hey guys i hope you enjoyed the
15:33
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