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BIOLOGY 1408 Chapter 3-lecture 6

Dr. C. Doumen

Lipids v Lipids are diverse compounds that are grouped

together because they do not mix well with water. They are thus hydrophobic . Why ?

v All lipids consist mainly of carbon and hydrogen atoms with just a few functional groups

–  Have large hydro-carbon chains

–  Linked by nonpolar covalent bonds

–  Hydrophobic (water-fearing)

v Lipids don’t form huge macromolecules or polymers like sugars, proteins and nucleic acids do.

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Lipids v Lipids are classified according to their organization.

The major classes are :

v Fats ( also called neutral lipids, triglycerides)

v Phospholipids

v Cholesterol based lipids

Fats v The fats are also called the tri-glycerides

v  A fat is a combination between 3 fatty acids and a molecule of glycerol.

v A fatty acid is a long hydro-carbon chain ending with a carboxyl group. In a simple way, we can write a generic fatty acid as follows:

hydrocarbon tail carboxyl group

CH3 - (CH2)n - COOH

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Example of a fatty Acid

Saturated vs Unsaturated Fatty Acids

v  Some fatty acid will have the maximum number of hydrogens on their carbons ( thus no double bonds between carbon atoms)

v  Those are called the saturated fatty acids

v  If a double bond is present , it is is called an unsaturated fatty acid (mono-unsaturated contain 1 double bond per fatty acid; poly-unsaturated contain 2 or more).

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Examples

Triglycerides v  Tri-glycerides are a linkage of 3 fatty acids to

a glycerol molecule

Glycerol

Fatty acid where R represents the rest of the fatty acid chain In a dehydration synthesis reaction, water (the HHO) will be removed to form a covalent bond between each fatty acid and the glycerol molecule

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Triglycerides

Dehydration synthesis linking one fatty acid to glycerol

Do this 3 times and we have a tri-glyceride

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Fats and Fatty Acids v  So why is this fat hydro-phobic ?

v  Once the fatty acid hook up with glycerol, no functional groups are left; they are all involved in a bond

v  It is mostly hydro-carbons with a few “buried” oxygens.

Fats and fatty acids

v This is your long term energy reservoir molecule. When you are low on carbohydrates, your body will start using these fats.

v Triglycerides are fats from the food we eat that are carried in the blood. Most of the fats we eat, including butter, margarines and oils, are in triglyceride form.

v Excess calories, alcohol or sugar in the body turn into triglycerides and are stored in fat cells throughout the body.

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Fats and Nutrition v  Fats with saturated fatty

acids tend to pack closer to each other and form aggregates easier

v  Animal fats are mostly made from saturated fats and thus are in general solid at room temperature

v  Plant Oils contain mostly unsaturated fats (liquid at room temp.)

Fats and Nutrition

v  The body can synthesize most of the fats it needs from the diet. However, two essential fatty acids, linolenic and linoleic acid, cannot be synthesized in the body and must be obtained from food.

v  The general consensus is to reduce food with larger amounts of animal fat (saturated fats).

v  These basic fats, found in seafood, plant, nuts,… are used to build other specialized fats called omega-3 and omega-6 fatty acids.

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Fats and Nutrition v  Omega-3 and omega-6 fatty acids are

important in the normal functioning of all tissues of the body and seem to be essential to fight inflammation.

v  A typical American diet has way too much Omega 6 compared to Omega 3

v  This imbalance seems to be at the basis of modern western diseases.

Fats and Nutrition

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PhosphoLipids v  A phospho-lipid is a special case of

a tri-glycerides

v  One of the fatty acids has been replaced with a functional charged phosphate group.

v  The molecule becomes hydrophillic at one end (the polar head) and remains hydrophobic at the other end due to the two fatty acid tails.

v  Phospholipids are essential in creating cellular membranes.

Polar head region

Steroids All steroids are made from the basic cholesterol molecule

v  cholesterol is a main component in cell membranes

v  cholesterol, is also important since it is the basic structure for making a variety of hormones.

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Steroids v  Anabolic steroids are

synthetic variants of the male sex hormone testosterone

v  They thus will mimic the real hormone ; sometimes with good, often with bad side effects (mood swings, infertility, cancers, inappropriate muscle mass, skin rashes, baldness,…)

Proteins v Proteins are essential to the structures and activities of

life

v Proteins are the most variable of macromolecules and thus perform an enormous variety of functions.

v  Proteins are involved in all aspects of cellular activity

v They can be functional such as enzymes, antibodies, hormones or structural such as collagen, nails, hairs.

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Proteins v The basic building block (the monomer) of all proteins

are amino acids . A protein is thus a polymer of amino acids

H

H

N

H

C

R

C

O

OH

Amino group

Carboxyl (acid) group

A typical amino acid has

•  A central carbon

•  A carboxyl group on one end

•  An amino group on the other end

•  A variable group (R)

Proteins v  There are 20 different amino acids, their differences due

to a change in the –R group.

v Each amino acid will thus have different characteristics

H

H

N

H

C

CH2

CH

CH3 CH3

CO

OH

H

H

N C

H

CH2

OH

CO

OH

H

H

N C

H

CO

OH CH2

COH O

Leucine (Leu)

Serine (Ser) Aspartic acid (Asp)

Hydrophobic Hydrophilic

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Proteins v Cells link amino acids together by dehydration

synthesis v The bonds between two amino acid monomer is

called a peptide bond and forms a di-peptide

H

H

N C C O

OH H

H N + C

H

R

C O

OH H2O

H

H

N C C N C C

R H R OH

O

Peptide bond

Dipeptide Amino acid

Dehydration reaction

Amino group

H

R

Amino acid

Carboxyl group

H O H

Figure 3.12C

Proteins v Many amino acids together form a polypeptide. v Polypeptides can be several to thousands of amino

acids long. v The different ways the amino acids are strung

together determine the kind of polypeptide it becomes

v The code for that arrangement is located in the genes in the DNA

v A functional protein can be one polypeptide or a combination of several polypeptides.

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Protein Structure v Proteins become functional when they fold the

proper way into a 3 dimensional structure v That proper folding is determined by the linear

sequence of amino acids and how they eventually will interact with each other v  Primary structure of a protein = The linear sequence of AA

in a protein v  Tertiary structure = the 3-dimensional folding of the protein v  Quarternary structure = when different polypeptides

interact to form one (1) functional protein

Protein Structure

The primary sequence tells us exactly in what position an amino acid is located. Changing the location of 1 amino acid may result in a non-functional protein (protein may not fold right)

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Protein Structure Correct folding creates the unique shape that determines the protein’s function

Protein Structure The correct folding of a polypeptide creates regions and grooves that enable the protein to execute its function

Groove

Groove

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Protein Structure The nicotinic Na-channel is an example a quaternary level protein made out of 5 polypeptides (subunits), forming a channel barrel system.

Protein Structures Hemoglobin is another example a quaternary level protein made out of 2x2 polypeptides (2 alpha and 2 beta subunits), forming an O2 carrying protein.

There are about 280 million Hemoglobin molecules in each red blood cell.

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Protein Structure Denaturation : when the 3-dimensional structure falls apart due to changes in temperature or pH. This will result in loss of function.

Protein Structure We boil things to denature proteins and thus re-organize the structures for better taste or to “kill” the function of proteins that could possibly harm us. Exposing proteins to extreme acids or bases also denatures them ( what happens when you add lemon juice to milk ? )

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Nucleic Acids v  The nucleic acids form the last group of

macromolecules of living cells

v There are two main types of nucleic acids

v DNA = deoxy ribose nucleic acid

v RNA = ribose nucleic acid

Nucleic Acids v  All information to make all structures of an

organism is located in the chromosomes, which are bundles of macromolecules, mostly made out of DNA

v The linear sequence of a protein of an organism for example, is coded within a gene, which is a specific sequence within the DNA of that organisms chromosomes.

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Nucleic Acids

A human karyotype : a display of all the chromosomes of an individual.

Nucleic Acids

v  The chromosomal DNA contains thousands of genes and each gene codes for a protein.

v The genes however do not make the proteins directly

v Information is first “passed on” to another molecule called RNA

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Nucleic Acids

v The flow of information is thus from DNA to RNA first: this is called transcription

v A protein is then manufactured off this RNA information : this is called the translation process.

Nucleic Acids v Nucleic acids such as DNA and RNA serve as the

blueprints for proteins and thus control the life of a cell

Sugar

OH

O P O

O-

CH2

H

O

H H

OH H

H

N

N

H

N

N H

H H N

Phosphate group

Nitrogenous base (A)

v  The monomers (building blocks) of nucleic acids are nucleotides.

v  They are composed of v  a 5 carbon sugar, v  a phosphate group v  a nitrogenous

base

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Nucleic Acids v  Nucleic Acids are

formed by stringing Nucleotide monomers together using the sugars and phosphates as the backbone

v The nitrogenous bases will stick out like the steps of a ladder.

Nucleic Acids: DNA

v  DNA never appears as a single strand

v  It will always be coupled in a helical fashion with another complementary DNA strand.

There are 4 such bases in DNA : adenine (A), thymine (T), cytosine

( C), and guanine (G)

Sugar-phosphate backbone

T

G

C

T

A Nucleotide

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Nucleic Acids: DNA v  There is only one complementary

strand of DNA that can pair up with an existing DNA strand

v  This is due that a nucleotide with an “A” base can only form hydrogen bonds with a nucleotide on the other strand that has a “T” base.

v  And “G” always pairs up with “C”

v  The result is a double helix of DNA held together only by hydrogen bonds.

C

T A

G C

C G

T A

C G

A T

A

G C

A T

A T

T A

Base pair

T

Nucleic Acids: DNA v  Because of this base pair ruling,

the two strands are called complementary (mirror images almost)

v  If you know the sequence on one strand, one can predict the sequence of bases on the other strand

v  -ACCAGT- on one strand must read as -TGGTCA- on the other strand.

C

T A

G C

C G

T A

C G

A T

A

G C

A T

A T

T A

Base pair

T

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Nucleic Acids: RNA v  While DNA is a double stranded helix (double helix),

RNA is usually single stranded

v  RNA also has a different sugar compared to DNA : DNA has a deoxy-ribose sugar, RNA has a ribose sugar ( they differ only the the absence/presence of one oxygen atom).

v  Another difference is that Thymine (T) is not present in RNA : it becomes replaced with a different base called Uracil (U).

Nucleic Acids: RNA

While DNA is a double stranded helix ( double helix), RNA is single stranded

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Nucleic Acids: RNA

While DNA has deoxyribose as the sugar in nucleotides, RNA has ribose as the sugar while the thymine base becomes replaced with Uracil.

DNA Application : Forensics

Electrophoretic analysis of DNA yields a unique pattern called a DNA fingerprint.

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DNA Forensics v  Depending on the

technique used, a person’s DNA shows up just like a Barcode

v  In this case, only a few markers identified individuals, but enough ‘markers’ were present to identify the suspect.

DNA Humor