Bio1 10/7 Lecture: Nucleic Acid and Lipids + Pre-Class Videos

For nucleic acids, the nitrogenous base and phosphate group are linked to which carbons of the pentose sugar?

The base is always bonded to the 1 prime (1’) carbon.

The phosphate group is always bonded to the 5’ carbon.

What is a triphosphate monomer? Name one.

A monomer that has three phosphate groups linked in a chain.

A free nucleotide is a triphosphate monomer.

Identify and compare Purines vs Pyrimidines

Purines include adenine and guanine. They have two cyclic rings.

Pyrimidines include cytosine, thymine, and uracil. They have one cyclic ring.

How do nucleotides link together to form chains?

What is the bond called?

What is this reaction and its byproduct?

Covalent bonds are formed between the 3’ hydroxyl group of one nucleotide and the 5’ phosphate group of another nucleotide.

A phosphodiester bond forms between the oxygen of the hydroxyl group and the phosphorus of the phosphate group closest to the 5’ carbon, which will break off the other two phosphate groups.

This is a condensation reactions that releases pyrophosphate (the remaining two phosphate groups bonded together).

Is the process of linking together nucleotide chains a spontaneous reaction? Explain.

Yes, it is a spontaneous reaction.

The condensation reaction itself is not favorable but the pyrophosphate released in the condensation reaction will break apart through hydrolysis into two individual phosphate groups which is very energetically favorable.

Compare the two ends of a nucleotide chain.

The two ends of a nucleotide chain are chemically distinct.

There is a 3’ end with an unbound hydroxyl group bonded to the 3’ carbon. Every nucleotide chain has exactly one unbound 3’ hydroxyl group.

There is a 5’ end with either one or three (linked) phosphate groups bonded to the 5’ carbon.

In what direction are nucleotide chains built? What word describes this?

Nucleotide chains are always extended unidirectionally in the 5’ to 3’ direction.

Enzymes always add single nucleotides to the 3’ end of the chain.

How does DNA form a double-stranded helix?

Include “complementary strands”. Discuss each type of base specifically.

Two separate DNA strands interact non-covalently and form hydrogen bonds between their nitrogenous bases.

Complementary strands have antiparallel base sequences, meaning they have opposite directionality.

Complementary bases pair in specific and predictable interactions. One purine will always pair with one pyrimidine.

• A can form two hydrogen bonds with T or U.

• C can form three hydrogen bonds with G.

What should you know about the relative percentages of nitrogenous bases in a double-stranded DNA?

The % of A and T are the same.

The % of C and G are the same.

It is important to know that this does not apply to single-stranded DNA.

How do mutations happen relative to nitrogenous bases?

A mutation changes the nitrogenous base sequence of DNA.

The trait is the entire DNA sequence and the mutated sequence is one form of the trait.

What is the typical writing convention for writing one strand of DNA or RNA?

The DNA or RNA sequence is written from 5’ to 3’, and with letters representing the base sequence in between.

Ex: 5’-GAT-3’

Is RNA always single-stranded?

No, it can form double strand structures though it is often single-stranded.

How does RNA form complex 3D structures even with only one strand?

Hydrogen bonds can form between bases within the same strand of RNA

Why is RNA more unstable than DNA?

The hydroxyl group bonded to the carbon-2 in its ribose sugar makes it much more reactive.

Can RNA and DNA pair together?

Yes, they can pair to create a double helix structure.

Describe the general structure of lipids and its properties.

Lipids are large groups of molecules composed mostly of hydrocarbons, which are chains of C and H atoms.

They are nonpolar and insoluble in water.

What are the main functions of lipids?

Stores energy

Forms cell membranes

Provides thermal insulation in animals (as fat)

What is the most common group of lipids? Describe its general structure and how it forms.

Triglycerides consist of one glycerol molecule and three fatty acids.

• A glycerol molecule consists of three carbons each bonded to a hydroxyl group.

• Fatty acids are amphipathic, meaning they contain a long nonpolar hydrocarbon chain (the hydrophobic tail) and a shorter polar COOH group (the hydrophilic end).

The polar end of the fatty acid bonds to the glycerol molecule through condensation, which releases a water molecule.

Three condensation reactions must occur to form one triglyceride.

Describe the polarity of triglycerides.

They are mostly nonpolar because a majority of its structure (in size) is nonpolar though it does have small polar parts.

What are the main two types of triglycerides?

Fats and oils

What is a mixed triglyceride?

A triglyceride that contains different fatty acids, instead of just the three same fatty acids.

This is more common in nature.

Compare saturated vs unsaturated fatty acids.

A saturated fatty acid has no carbon-carbon double bonds, so all of its carbons are fully saturated with hydrogen.

An unsaturated fatty acid has at least one carbon-carbon double bond.

• A monounsaturated fatty acid has only one carbon-carbon double bond.

• A polyunsaturated fatty acid has multiple carbon-carbon double bonds.

What are the two types of carbon-carbon double bonds in fatty acids? Compare them.

How do they impact the structure of triglycerides?

Trans and cis configurations.

The cis configuration has both hydrogen atoms on the same side of the carbon-carbon bond.

• It creates significant bends/kinks in the hydrocarbon chain because the double bonds can’t rotate freely.

• These bends prevent fatty acids from tightly packing together.

The trans configuration has the hydrogen atoms on opposite sides of the carbon-carbon bond.

• It does not have any significant bends, so the molecule is much closer in structure to an unsaturated fatty acid than to a cis-configuration saturated fatty acid.

• The fatty acids can pack together very tightly.

Why do fats and oils exist in different states of matter at room temperature?

Fats contain saturated fatty acids which are tightly packed together and allows the fat to be solid at room temperature.

Oils contain cis-unsaturated fatty acids which can’t pack together as tightly, which makes the oils liquid at room temperature.

What are transfats? Why are they considered unhealthy?

Unsaturated fatty acids that contain trans-double bonds. They are found in limited amounts in nature but can be created through food processing.

They are correlated with increased risk of coronary heart disease.