07 lipids and proteins and nucleic acids

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Lipids

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Functions of Lipids• Energy storage

– In the form of fat in humans and oil in plants

• Heat insulation– A layer of fat under the skin

reduces heat loss

• Buoyancy– Lipids are less dense than

water to help animals to float

• To provide a layer of protection– Fat on your body – Membranes in cells

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Triglycerides (FAT)

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Examples of saturated and unsaturated fats and fatty acids 

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The structure of a phospholipid

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Two structures formed by self-assembly of phospholipids in aqueous environments   

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Cholesterol, a steroid    

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Steroids include cholesterol and certain hormones

• Steroids are lipids with a carbon skeleton consisting of four fused carbon rings.– Different steroids are created by varying

functional groups attached to the rings

• Cholesterol, an important steroid, is a component in animal cell membranes.

• Cholesterol is also the precursor from which all other steroids are synthesized.

www.pearsonsuccessnet.com activity 5.3 page 3

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Using Carbohydrates and Lipids in Energy Storage

• Both lipids and carbs can be used for energy storage in living organisms. Both types of storage compound have advantages. Carbohydrates are usually for energy storage over short periods and lipids for long-term storage

Advantages of Lipids

Advantages of Carbs

Lipids contain more energy per gram than carbs so stores of lipids are lighter than stores of carbs that contain the same amount of energy

9 kcal/g

Carbohydrates are more easily digested than lipids so the energy stored by them can be released more rapidly

4 kcal/g

Lipids are insoluble in water, so they do not cause problems with osmosis in cells

Carbohydrates are soluble in water so are easier to transport to and from the storage area

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Proteins

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C C N H

H H

R O

OH

amine functional group

carboxylic acid functional group

R-group changes depending upon the amino acid

basic structure of an amino acid

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• The R-group (outlined in white) changes the properties of each amino acid

• ex: nonpolar groups are hydrophobic

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• polar R-groups are hydrophilic• electrically charged R-group will interact with

molecules of opposite charge

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peptide bond formation

amino acid chain = polypeptide chain

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The primary structure of a

protein: CHAIN• primary protein

structure: – polypeptide chain

• The folding of a protein from a chain of amino acids occurs spontaneously

• The precise primary structure of a protein is determined by inherited genetic information.

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Secondary Structure: α Helix and β Pleated Sheets

• The secondary structure of a protein results from hydrogen bonds at regular intervals along the polypeptide backbone.

• Typical shapes that develop from secondary structure are coils (an alpha helix) or folds (beta pleated sheets).

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Tertiary Structure: Twists in on itself • Tertiary

structure is determined by a variety of interactions among R groups and between R groups and the polypeptide backbone.

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The quaternary structure of proteins: multiple chains together

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Spider silk: a structural protein• The structural properties of silk are due to beta

pleated sheets.– The presence of so many hydrogen bonds makes each

silk fiber stronger than steel.

http://www.sciencedaily.com/releases/2008/02/080214114448.htm

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• A functional proteins consists of one or more polypeptides that have been precisely twisted, folded, and coiled into a unique shape.

• It is the order of amino acids that determines what the three-dimensional conformation will be.

A protein’s function depends on its specific conformation

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At present, scientists use X-ray crystallography to determine protein conformation.

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Denaturation and renaturation of a protein

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An Overview of Protein Functions

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enzymes: specialized proteins

ribonuclease

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Nucleic Acids

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The Nucleotide Subunits of DNA• Although DNA is the genetic

material of living organisms and is therefore of immense importance, it is made of relatively simple subunits

• These are called nucleotides• Each nucleotide consists of

three parts:– A sugar, deoxyribose– A phosphate group– And a nitrogen base

• DNA nucleotides do not all have the same base

• Four different bases are found– Adenine, guanine, cytosine, thymine

BS

P

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nucleotide monomer

phosphate group

deoxyribose sugar

nitrogen base

1’

5’

2’3’

4’

CH2

Numbering the carbons on deoxyribose: 1’ = nitrogen base3’ = hydroxyl group5’ = phosphate group

OH

PO4

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Building DNA Molecules• Two DNA nucleotides can be

linked together by a covalent bond between the sugar of one nucleotide and the phosphate group of the other

• More nucleotides can be added in a similar way to form a strand of nucleotides

• DNA molecules consist of two strands of nucleotides wound together into a double helix

• Hydrogen bonds link the two strands together

• These form between the bases of the two strands

• However, adenine only forms hydrogen bonds with thymine and cytosine only forms hydrogen bonds with guanine

• This is called complementary base pairing

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•The bonds between the phosphate group and the deoxyribose sugar on an individual nucleotide is a covalent bond – phosphodiester bond.

•Phosphodiester bonds are arranged phosphate – oxygen – carbon.

•Bonding nucleotides together: occurs between 3’ OH group on one nucleotide and 5’ phosphate group on the other through a condensation reaction (release of water)

•There will always be a free 5’ end 3’ on each strand of DNA

5’

3’

•Strands run antiparallel to each other = one strand has the 5’ C on the top, 3’ C on the bottom, and the other is reversed

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NUCLEOSOME STRUCTURE: - 8 histones, (+) charged, (protein) in the core - 2 molecules of 4 different histones- DNA, (-) charged, wraps around the core 2x- 1 histone holds the 2 ends of the DNA, histone H1- with 2 ends of linker DNA- nucleosomes help to supercoil chromosomes and help to regulate transcription

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In nuclear DNA there are three types:

1. Unique/Single-copy genes:- genes with coding functions- essential to producing proteins- Human Genome Project: to sequence all the coding genes, less than 2% of chromosomes are coding genes

- Coding parts of DNA are not strung together neatly; there are noncoding regions interspersed within between coding regions

- coding parts = EXONS; noncoding parts = INTRONS - EXONS are allowed to EXIT the nucleus to be translated into a protein- INTRONS must stay IN the nucleus because they don’t code for a protein

2. Highly repetitive sequences: - found in eukaryotes- from 5%-45% of the total genome- 5-300 base pairs per sequence - Clustered together? = satellite DNA- usually dispersed throughout the genome = transposable

- Barbara McClintock; 1950

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RNA• Usually single

strands

• Unlike DNA, contains the pyrimidine base uracil in place of thymine

• Contains ribose sugar rather than deoxyribose sugar

• Three types are key players in protein synthesis