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Samenvatting Molecular Biology of the Cell Deel 1
- Instelling
- Rijksuniversiteit Groningen (RuG)
Samenvatting voor het eerste deel van het vak Molecular Biology of the Cell
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Voorbeeld 3 van de 24 pagina's
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Chapter 2: Cell Chemistry and BioenergeticsLife hinges on the chemical properties of water. H2O is highly polar because the O is strongly
attractive for electrons, which gives it a negative charge.
hydrogen bond: noncovalent bond in which an electropositive hydrogen atom is partially
shared by two electronegative atoms.
- Each water molecule can form these bonds through it’s two H atoms to two other water
molecules, which forms a network in which bonds are continually broken and formed
hydrophilic: dissolving readily in water (water-loving)
- Alcohols, most proteins, sugars
Hydrophobic: not dissolving readily in water (water-fearing)
- Hydrocarbons
There are three types of noncovalent bonds: electrostatic attractions, hydrogen bonds and van
der Waals attractions; and a fourth factor which pushes molecules together, the hydrophobic
force. Their energies working together can create a strong force, individually the forces are
weak.
electrostatic attractions: a noncovalent, ionic bond between two molecules carrying groups
of opposite charge
Van der Waals attractions: type of (individually weak) noncovalent bond that is formed at
close range between nonpolar atoms
Hydrophobic force: force exerted by the hydrogen-bonded network of water molecules
that brings two nonpolar surfaces together by excluding water
between them. (also happens in RNA and DNA)
When a polar molecule becomes surrounded by water, the proton will be attracted to the partial
negative charge on the O atom creating a hydronium ion.
proton: Positively charged subatomic particle that forms part of an atomic
nucleus. Hydrogen has a nucleus composed of a single proton
hydronium ion: Water molecule associated with an additional proton. The form generally
taken by protons in aqueous solution.
acids: A proton donor. Substance that releases protons when dissolved in water,
forming hydronium ions and lowering the pH.
- characterized as strong or weak, depending on how readily they give up protons
- the concentration of the H3O+ in cells has to be regulated closely because of how readily
they give up protons.
base: A substance that can reduce the number of protons in solution, either by
accepting H+ ions directly or by releasing OH- ions which then combine
with H+ to form H2O
buffers: Solution of weak acid or weak base that resists the pH change that would
otherwise occur when small quantities of acid or base are added.
- weak bases are important in living cells because they have a weak tendency to
reversibly accept a proton from water.
,chemical group: Certain combinations of atoms, such as methyl (-CH3), hydroxyl (-OH_),
carboxyl (-COOH), carbonyl (-C=O), phosphate (-PO32-), sulfhydryl (-SH) and amino (-NH2), that
have distinct chemical and physical properties and influence the behavior of the molecule in
which the group occurs.
macromolecules: Polymers constructed of long chains of covalently linked, small organic
(carbon containing) molecules. The principal building blocks from which a
cell is constructed and the components that confer the most distinctive
properties of living things.
- example: proteins, they act as enzymes, structural components, molecular motors
- each polymer grows by the addition of a monomer onto the end of a growing chain with
a condensation reaction.
- the shape of macromolecules are highly constrained because of the many weak
noncovalent bonds that form between different parts of the same molecule. → gives
enzymes their specific task because of their unique shape. (determined by the sequence
of the monomers)
IN BOOK: Panel 2-3, 2-4, 2-5, 2-6
monosaccharides: either contain an aldehyde (H-C=O) group (aldoses) or a ketone (-C=O)
group (ketoses)
- in aqueous solution aldehyde or ketone group reacts with a hydroxyl group of the same
molecule and forms a ring.
- beta hydroxyl: upwards, alpha hydroxyl: downwards
disaccharides: the carbon that carries the aldehyde or ketone group can react with any
hydroxyl group on a second sugar molecule
- maltose (glucose + glucose), lactose (galactose + glucose), sucrose (glucose + fructose)
polysaccharides: name for long chains, short chains are called oligosaccharides.
fatty acids: unsaturated (double bond, liquid) and saturated (no double bond, solid)
- stored as an energy reserve, linked to glycerol
- phospholipides are the major constituents of cell membranes (hydrophilic head and
hydrophobic tail)
bases: pyrimidine (C,U,T) or purine (A,G)
nucleoside: sugar + base
nucleotide: sugar + base + phosphate (<-- makes it negatively charged)
- buildingblocks for DNA
, Chapter 3: Proteins
Proteins, apart from building blocks, execute the majority of the cell’s functions:
- enzymes → provide the intricate molecular surfaces inside a cell that catalyze its many
chemical reactions.
- in the plasma membrane → form channels and pumps that control the passage of small
molecules into and out of the cell.
- providing information for mechanisms in and outside the cell
- antibodies, toxins, hormones, antifreeze molecules, elastic fibers, ropes or sources of
luminescence
The shape of a protein is specified by its amino acid sequence. There are 20 different amino
acids.
protein: the major macromolecular constituent of cells. A linear polymer of
amino acids linked together by peptide bonds in a specific
sequence.
polypeptide backbone: Repeating sequence of atoms along the core of the polypeptide
chain
side chains: The part of an amino acid that differs between amino acid types.
The side chains give each type of amino acid its unique physical
and chemical properties.
- side chains can be nonpolar, uncharged polar, acidic or basic
- many weak bonds acting in parallel can hold two regions of a polypeptide chain tightly
together.
- the single bonds between the amino acids allow for rotation (psi and phi rotation)
- basic side chains: at neutral pH they will be positively charged. (histidine is only partly
neutral, very weak)
- acidic: at neutral pH they are negatively charged.
- nonpolar side chains tend to cluster in the interior of the molecule (hydrophobic forces),
polar groups tend to arrange themselves near the outside.
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