Some General Functions of Water in Cells - Lecture Slides | BIO 311C, Study notes of Biology

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BIO 311CSpring 2009

Lecture 12 – Wednesday 18 Feb.

Some General Functions of Water in Cells

It is a solvent for most biological molecules. It is a powerful orienting force for those molecules, and parts ofmolecules, that don't dissolve in it. It provides a medium for effective intracellular movement of moleculesand cell components. It provides an appropriate environment for the chemical reactions thatoccur in cells (metabolic reactions). It participates directly as a reactant or product in many metabolicreactions. It is a source and sink for H

+^ Oand OH 3

-^ ions. These ions also participate

in many biological reactions and they stabilize the 3-dimensional shapesof many biological molecules. It provides stability in a constantly changing environment.

+- K-^ - - -

+ K + K + K

Cations often neutralizeanions on the surfacesof biological membranesand macromolecules.

• +Mg + -

Divalent cations, especially2+Mg, often serve as "saltbridges" within a biomoleculeor between two biomolecules.

Iron (Fe

2+) is a component of the blood protein hemoglobin. It binds covalently to O

, thus transporting oxygen throughout the 2

body.

From Textbook Fig. 5.21, p. 83

Some general Functions

Performed by Inorganic Ions in Cells

• They balance electrical charges on biological molecules, therebystabilizing their structures (especially K

+^ and Mg

• They serve as structural components by acting as an electrical bridgebetween two charged functional groups within a single molecule or elsebetween two separate molecules (primarily Mg

• They help buffer cell components at desired pH values (especiallyphosphate). - They bond covalently, electrovalently or in other ways to somebiological molecules (e.g. Fe

• They act as coenzymes (cooperating with enzymes) in many enzyme-catalyzed reactions (especially Mg

• They participate directly in reduction-oxidation reactions (especially2+Fe

3+/Fe and Cu

+2+/Cu

• Their concentration in cells is carefully regulated in order to regulatethe rates of major metabolic processes (especially Ca

A very general way to identify an organic molecule is to indicatethe number of carbon atoms it contains. For example, an organicmolecule containing a total of 7 carbon atoms could bedescribed as a C

molecule. This designation by itself tells 7

almost nothing about the chemical, physical or biologicalproperties of the molecule, and doesn’t even indicate whichfunctional groups are present. But it is still sometimes useful. Example: from the to Exam 1

A C^5

molecule The colors are notsignificant for thisillustration.

Definition: A carbohydrate

is a simple sugar, a modified

sugar, or a polymer of a sugar. Thus, in order to understand carbohydrates it isnecessary to understand sugars.

aldehyde functional group

ketone functional group

C^

O H

C

C^ O

R^1

R^2

C^

O H

R

C O

C^

C

standard representation more descriptive representation The carbon atom that forms the aldehyde or ketone functional group must also becovalently bonded to another carbon atom or to a hydrogen atom. Aldehyde and ketone functional groups are very similar to each other in theirchemical properties and in their biological functions.

formula with all covalent bonds shown It is standard practice to show a sugar with the carbon atoms orientedvertically, and with the aldehyde or ketone functional group at (or nearto) the top of the molecule.

an acceptable slightly abbreviated structure,with not all covalent bonds shown

Structural Formula of a 6-carbon Sugar

D-glucose

Chemical formulas are generally not sufficient torepresent the chemical nature of sugars.^ Example: Two compounds, each with the chemical formula

CH^3

O, 63

but with very different structural formulas and evendifferent functional groups: a Csugar^3 ( CH^3

O) 63

a Ccompound that^3 is not

a sugar ( CHO 363

)

carboxylic acid functional group^ alcohol functional group^ methyl functional group

aldehyde functional group alcohol functional groups

Carbon atoms of sugars are numbered from the top down.

A C^5

sugar

A C^6

1 2 3 4 5 6 sugar^