macromolecules biology
DESCRIPTION
BiologyTRANSCRIPT
Proper&es of Macromolecules
Lecture 2
Overview
Proper&es of Carbon
Structure and Func&onal groups
Isomers
Polymers
Carbon: The Backbone of Life • Living organisms consist mostly of carbon-based
compounds
• Carbon is unparalleled in its ability to form large, complex, and diverse molecules
• Proteins, DNA, carbohydrates, lipids, and other molecules that distinguish living matter are all composed of carbon compounds
Biomolecules range in size and complexity
CO2 Carbon Dioxide
CH4N2O Urea
C6H12O6 Glucose
Large molecule Phospholipid
Macromolecules DNA
Supramolecular Complex Ribosome
Life exists even in harsh environments
Proper&es of Carbon • Contain carbon (C backbone) Why is carbon so special?
• Most contain H and O, but may contain other elements N = Nitrogen P = Phosphorus S = Sulfur
à Carbon can form 4 covalent bonds – bonds with up to 4 separate atoms – can bond with other C atoms
à long chains of carbon atoms
à can combine with many other kinds of atoms
Tetravalence in Carbon Can form 4 single bonds
C
H
H H
H
Methane
… 1 double bond and 2 single bonds
C O
H
Formaldehyde
H
… 2 double bonds
C O O
Carbon dioxide
… 1 triple bond & 1 single
C H N
Hydrogen Cyanide
Distinctive properties of an organic molecule depends on:
1. Carbon skeleton 2. Functional
groups – molecular components
attached to the carbon skeleton
– responsible for characteristic chemical reactions of the molecule
8
Together, these two characteris&cs give organic molecules dis&nc&ve physical and chemical proper&es and creates diversity among organic molecules
Carbon Skeletons • Made up of chains or rings • Skeletons differ in:
– length (number of carbons) – branching – number and position of double bonds
9
• In molecules with multiple carbons, each carbon bonded to four other atoms has a tetrahedral shape
• When two carbon atoms are joined by a double bond, the molecule has a flat shape
Hydrocarbons • Hydrocarbons: Organic
compounds composed only of carbon and hydrogen (no func&onal groups)
• Covalent, non-‐polar bonds between C & H
• Hydrocarbons are largely hydrophobic
Nucleus
Fat droplets
(b) A fat molecule (a) Part of a human adipose cell
10 µm
Func&onal Groups • Replacing H with func&onal groups changes
the characteris7cs of the molecule
• Most func&onal groups form ionic or hydrogen bonds with other molecules
• Gives hydrophilic proper&es (water soluble)
*Some func&onal groups are non-‐polar and may cause molecule to be hydrophobic
example:
These subtle variations in molecular architecture influence development of anatomical and physiological differences
Func&onal Groups Hydroxyl Group
• R-‐OH or HO-‐R (‘R’ => remainder of molecule)
• Hydroxyl groups are polar because electronega&ve oxygen
• Organic compounds having only hydroxyl groups are called alcohols (ethanol, methanol, etc.)
• Sugars owe their solubility in water to the presence of hydroxyl groups
Glucose molecule (red=O, light gray= H) Ethanol
Func&onal Groups Carbonyl Group:
Aldehydes and Ketones • R-‐C=O • Polar carbonyl groups, such as aldehydes and ketones a`ract
covalent electrons
• Aldehydes contain the carbonyl group bonded to the end of the carbon skeleton
• Ketones have the carbonyl group bonded within the carbon skeleton
Func&onal Groups Carbonyl Group: Aldehydes and
Ketones
Simple sugars can be aldehydes or ketones
Ketone
Aldehyde
Func&onal Groups Carboxyl Group
• R-‐COOH • Carboxyl groups are weakly acidic; in cells, this func&onal group is found in the ionized form COO-‐
• An important part of amino acids:
All amino acids contain a carboxyl group which can donate a hydrogen
aka. Carboxylic acid
Carboxyl Group… examples
• Other compounds that contain this functional group include:
• Formic acid a simple organic molecule released by formicine ants (which account for about 10% of the planet’s ants) as a defense mechanism
• Acetic acid, gives vinegar its sour taste
Formic acid Ace&c acid
h`p://www.youtube.com/watch?v=Sp8b1vVnQSY
Func&onal Groups Amino Group
• R-‐NH2
• Amino groups are weakly basic; under cellular condi&ons this func&onal group is found in the ionized form NH3
+
• Also an important part of amino acids:
All amino acids contain an amino group which can accept a hydrogen
Func&onal Groups
Amino Group
• Nitrogenous bases in DNA and RNA contain many amino groups…
Func&onal Groups Phosphate Group
• R-‐PO4H2
• Phosphate groups are weakly acidic; in cells, this func&onal group contributes a nega&ve charge to the molecule
• Phosphate groups are cons&tuents of:
Phospholipids
• Phosphate group contributes to the polarity of the head region
Func&onal Groups
Phosphate Group
Nucleic acids (building blocks of DNA and RNA)
=> hence, sugar-‐phosphate backbone due to alterna&ng sugar and phosphate
Func&onal Groups Phosphate Group
Adenosine Triphosphate
• Phosphate groups create instability in the molecule which is responsible for its high energy state
Func&onal Groups Sulhydryl Group
• R-‐SH • Helps stabilize protein structure
When two sulhydryl groups (func&onal group of amino acid cysteine) within a protein are facing each other, they oien form a disulfide bridge
STRUCTURE
CHEMICAL GROUP Hydroxyl
NAME OF COMPOUND
EXAMPLE
Ethanol
Alcohols (Their specific names usually end in -ol.)
(may be written HO—)
Carbonyl
Ketones if the carbonyl group is within a carbon skeleton
Aldehydes if the carbonyl group is at the end of the carbon skeleton
Carboxyl
Acetic acid Acetone
Propanal
Carboxylic acids, or organic acids
FUNCTIONAL PROPERTIES
• Is polar as a result of the electrons spending more time near the electronegative oxygen atom. • Can form hydrogen bonds with water molecules, helping dissolve organic compounds such as sugars.
• A ketone and an aldehyde may be structural isomers with different properties, as is the case for acetone and propanal. • Ketone and aldehyde groups are also found in sugars, giving rise to two major groups of sugars: ketoses (containing ketone groups) and aldoses (containing aldehyde groups).
• Found in cells in the ionized form with a charge of 1- and called a carboxylate ion.
Nonionized Ionized
• Acts as an acid; can donate an H+ because the covalent bond between oxygen and hydrogen is so polar:
Amino Sulfhydryl Phosphate Methyl
Methylated compounds Organic phosphates
(may be written HS—)
Thiols Amines
Glycine Cysteine
• Acts as a base; can pick up an H+ from the surrounding solution (water, in living organisms):
Nonionized Ionized
• Found in cells in the ionized form with a charge of 1+.
• Two sulfhydryl groups can react, forming a covalent bond. This “cross-linking” helps stabilize protein structure. • Cross-linking of cysteines in hair proteins maintains the curliness or straightness of hair. Straight hair can be “permanently” curled by shaping it around curlers and then breaking and re-forming the cross-linking bonds.
• Contributes negative charge to the molecule of which it is a part (2– when at the end of a molecule, as above; 1– when located internally in a chain of phosphates). • Molecules containing phosphate groups have the potential to react with water, releasing energy.
• Arrangement of methyl groups in male and female sex hormones affects their shape and function.
• Addition of a methyl group to DNA, or to molecules bound to DNA, affects the expression of genes.
Glycerol phosphate 5-Methyl cytidine
STRUCTURE
CHEMICAL GROUP Hydroxyl
NAME OF COMPOUND
EXAMPLE
Ethanol
Alcohols (Their specific names usually end in -ol.)
(may be written HO—)
Carbonyl
Ketones if the carbonyl group is within a carbon skeleton
Aldehydes if the carbonyl group is at the end of the carbon skeleton
Carboxyl
Acetic acid Acetone
Propanal
Carboxylic acids, or organic acids
FUNCTIONAL PROPERTIES
• Is polar as a result of the electrons spending more time near the electronegative oxygen atom. • Can form hydrogen bonds with water molecules, helping dissolve organic compounds such as sugars.
• A ketone and an aldehyde may be structural isomers with different properties, as is the case for acetone and propanal. • Ketone and aldehyde groups are also found in sugars, giving rise to two major groups of sugars: ketoses (containing ketone groups) and aldoses (containing aldehyde groups).
• Found in cells in the ionized form with a charge of 1- and called a carboxylate ion.
Nonionized Ionized
• Acts as an acid; can donate an H+ because the covalent bond between oxygen and hydrogen is so polar:
STRUCTURE
CHEMICAL GROUP Hydroxyl
NAME OF COMPOUND
EXAMPLE
Ethanol
Alcohols (Their specific names usually end in -ol.)
(may be written HO—)
Carbonyl
Ketones if the carbonyl group is within a carbon skeleton
Aldehydes if the carbonyl group is at the end of the carbon skeleton
Carboxyl
Acetic acid Acetone
Propanal
Carboxylic acids, or organic acids
FUNCTIONAL PROPERTIES
• Is polar as a result of the electrons spending more time near the electronegative oxygen atom. • Can form hydrogen bonds with water molecules, helping dissolve organic compounds such as sugars.
• A ketone and an aldehyde may be structural isomers with different properties, as is the case for acetone and propanal. • Ketone and aldehyde groups are also found in sugars, giving rise to two major groups of sugars: ketoses (containing ketone groups) and aldoses (containing aldehyde groups).
• Found in cells in the ionized form with a charge of 1- and called a carboxylate ion.
Nonionized Ionized
• Acts as an acid; can donate an H+ because the covalent bond between oxygen and hydrogen is so polar:
Review Func&onal groups
OH
C O
CO
OH
NH
H
P O-
O
O
O-
SH
Sulfhydryl
Amino
Hydroxyl group
Carbonyl
Carboxyl
Phosphate
1) Structural Isomers • Structural isomers have different covalent arrangements of
their atoms
à Isomers are compounds with the same molecular formula (i.e. the same numbers and types of atoms) but different structures and proper&es.
à Three important kinds for Biology:
Isomers
2) Geometric Isomers
• Geometric isomers have the same covalent arrangements but differ in spatial arrangements (arrangement around a double bond)
• Double bonds are rigid and do not allow the joined atoms to rotate freely
• As a result, two isomers are always possible if different groups are attached around a double bond
cis isomer trans isomer:
Example: Rhodopsin
11-cis retinal
All-trans retinal
photon
• The visual pigment rhodopsin in the human eye rotates around a double bond when hit by light at the back of the retina
• Enantiomers are isomers that are mirror images of each other • Usually consists of a carbon (i.e. asymmetric carbon) attached
to 4 different functional groups
3) Enan&omers
• Cells will recognize one enantiomer (i.e. biologically active) but not the other
L isomer D isomer
• Two enantiomers of a drug may have different effects
• This demonstrates that organisms are sensitive to even subtle variations in molecules
L-Dopa (effective against Parkinson’s disease)
D-Dopa (biologically
Inactive)
Ex: L-Dopa
Example: Drug Enan&omers
Macromolecules
• Macromolecules are large molecules composed of thousands of covalently connected atoms
à small organic molecules are joined together to form larger molecules (aka polymers)
• The architecture of a macromolecule helps explain how that molecule works
Hydrolysis adds a water molecule, breaking a bond
Short polymer Unlinked monomer
Dehydra&on removes a water molecule, forming a new bond
Longer polymer
Monomers form larger molecules by condensa&on reac&ons (dehydra&on reac&ons)
Synthesis
Requires: energy and catalyst
Breakdown Polymers are disassembled to monomers by hydrolysis (the reverse)
Occurs passively, but cells use a catalyst
Synthesis and Decomposi&on Reac&ons
4 Main Classes of Biomolecules
1. Carbohydrates
2. Lipids
3. Proteins
4. Nucleic Acids
Polymer? Monomer
NO
SOME MONOSACCHARIDE
ALL AMINO ACID
ALL NUCLEOTIDES
NA
Lecture 3: Learning Objec&ves - Describe the importance of carbon in living organisms - List and describe the two properties of Organic Compounds - Know the structure, functions and give an example for the
main functional groups (hydroxyl, carbonyl, carboxyl, amino, sulphydryl, and phosphate)
- Know the difference between structural isomers, geometric isomers and enantiomers
- Understand dehydration and hydrolysis reactions - Name the four classes of Macromolecules
Next Lecture: Carbohydrates (ch. 3)