Samenvatting voor het vak Celbiologie, Avans Hogeschool, Forensisch Laboratorium Onderzoek jaar 1. Ook voor Biologie en Medisch Laboratoriumonderzoek studenten. Deze samenvatting bestaat uit de hoofdstukken 5, 7, 8, 9 en 12 van het boek Biology: A Global Approach
Samenvatting Celbiologie 2017/2018
Les 1: Macromolecules (5.1 t/m 5.5)
Large carbohydrates, proteins and nucleic acids are called polymers.
Polymers consist of many monomers which are linked by covalent bonds.
The reaction connecting monomers to form a polymer, is called a
dehydration reaction. In this reaction, a hydroxyl-group (-OH) from the
first monomer and a hydrogen (-H) from the second monomer form a
water molecule (H2O) and is released from the reaction. When more and
more monomers are added to the chain it is also called polymerization.
Polymers can also be disassembled. This reaction is called hydrolysis.
This is the reverse of the dehydration reaction. Hydrolysis means water
breakage. A water molecule (H2O) is added to the polymer and the
hydrogen (-H) attaches to one monomer and the hydroxyl-group (-OH)
attaches to the other monomer.
There are four types of macromolecules:
1. Carbohydrates
Carbohydrates are sugars and polymers of sugar. The simplest
carbohydrate is a monosaccharide (also called a simple sugar). Two
monosaccharides are linked by a glycosidic linkage (which is a covalent
bond) and make a disaccharide. The polymers of carbohydrates are
called polysaccharides.
A sugar is either an aldose or a ketose. It
depends on the placement of the carbonyl
group (-C=O). An aldose has the carbonyl
group at the end of the chain and the
ketose has the carbonyl group in de middle
of the carbon chain.
Another classification of sugars is the size
of the carbon skeleton. Sugars with three
carbons are called triose. Sugars with five
carbons are called pentose and sugars
with six carbons are called hexose.
In aqueous solutions, glucose and many other five- and six-carbon sugars
form rings, because rings are more stable. When glucose forms a ring, the
hydroxyl group (-OH) attached to the #1 carbon is positioned either below
or above the plane of the ring. When it is placed below the plane of the
ring, it is called an alpha (α). When it is placed above the plane of the
ring, it is called a beta (β).
A few carbohydrates:
Glucose + glucose = maltose
Glucose + fructose = sucrose
Glucose + galactose = lactose
,Both animals and plants store sugars for later use. Plants store sugars in
the form of starch. This is a polymer of alpha glucose. Animals store
sugars called glycogen. This is a polymer of glucose. It is stored in the
liver and muscle cells. Hydrolysis of glycogen makes glucose which can be
used as sugar when needed.
Cellulose is a polysaccharide and is a major component for plant cell
walls. It is built from alpha and beta glucoses.
Chitin is the carbohydrate made of beta glucoses with a nitrogen-
containing attachment. Chitin is used by insects and spiders to build the
exoskeleton which is a hard case that surrounds the soft parts of the
animal. The case becomes hardened when the proteins are chemically
linked to each other.
2. Lipids
There are three types of lipids:
Fats
A fat consists of glycerol and three fatty acid chains, joined by an ester
linkage, which is a dehydration reaction between a hydroxyl group (-OH)
and a carboxyl group (-COOH). Glycerol is an alcohol. A fatty acid is a
carbon chain made of 16 or 28 carbon atoms in length. The glycerol-head
of the fat is hydrophilic. The fatty acid chains are hydrophobic.
A saturated fatty acid are “saturated” with
hydrogen, which means there are no double
bonds. Saturated fats are solid at room
temperature. An unsaturated fatty acid has
double (cis) bonds, making a kink in the chain.
Unsaturated fats are liquid at room
temperature.
The process of hydrogenating vegetable oils
produces not only saturated fats but also fats
with trans double bonds. Trans fats can
contribute in coronary heart diseases.
The major function of fats is energy storage. Animals and humans store
their long-term food reserves in adipose cells, which are cells in the
connective tissue specialised in synthesizing and containing large bulbs of
fat.
Phospholipids
Phospholipids are a major component of cell membranes. A phospholipid
consists of a glycerol group with a phosphate group and a choline group
(this group is variable) attached to it. This makes the hydrophilic head. The
hydrophobic tail consists of two fatty acid chains with cis double bonds,
making a kink in the chain. When phospholipids are added to water, they
, form a lipid bilayer. The heads turn outwards,
towards the water. The tails turn inwards,
towards each other. The phospholipid bilayer
forms a boundary between the cell and its
external environment.
Steroids
Steroids are lipids
characterized by a carbon
skeleton consisting of four fused
rings. Steroids vary in the
chemical groups attached to the
four fused rings. Cholesterol, a
type of steroid, is a crucial
molecule in animals. It is a
component of animal cell
membranes. A high level of cholesterol may contribute to atherosclerosis.
3. Proteins
Proteins are all structured from the same 20 amino acids, linked in
unbranched polymers. The bond between amino acids is called a peptide
bond, which makes a polymer of amino acids a polypeptide. They link
while releasing a water molecule. One end of the polypeptide has a free
amino group (the N-terminus) and the other end has a free carboxyl
group (the C-terminus).
Proteins are biologically functional molecules made up of one or more
polypeptides, each folded and coiled into a specific three-dimensional
shape. An amino acid is an organic molecule with both an amino group (-
NH2) and a carboxyl group (-COOH). The carbon at the center of the amino
acid, is called the alpha carbon. The alpha carbon has an amino group, a
carboxyl group, a hydrogen atom and a side chain group (R) with differs
with each amino acid.
Examples of proteins:
- Enzymatic proteins; these selectively accelerates chemical reactions.
- Defensive proteins; these protect the body against diseases.
- Storage proteins; these store amino acids.
- Transport proteins; these transport substances.
- Hormonal proteins; these coordinate the activities of an organism.
- Receptor proteins; these respond to chemical stimuli.
- Contractile and motor proteins; these arrange movement.
- Structural proteins; these support the cells.
There are four levels of protein structure. The primary structure is the
sequence of the amino acids of the protein. The secondary structure is
the folding and coiling of the sequence. There are two types of secondary
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