Biological Science Freeman Chapter 4

Nucleic Acids

-The polymer subunits that make up nucleotide monomers

1. phosphate group

2. five carbon sugar

3. nitrogenous (nitrogen containing) base

-both the the phosphate group and nitrogenous base are bonded to the sugar molecule

1. phosphate group

2. five carbon sugar

3. nitrogenous (nitrogen containing) base

-both the the phosphate group and nitrogenous vase are bonded to the sugar molecule

Nucleotides

Basic units of DNA molecule, composed of a phosphate, which is bonded to a 5-carbon sugar, and one of 4 DNA bases

Ribonucleotides

-monomers of RNA

-sugar is ribose

-has an -OH group bonded to the 2' carbon

Deoxyribnucleotides

-monomers of DNA

-sugar is deoxyribose ("lacking oxygen")

-has H instead at 2' carbon

deoxyribonucleic acid (DNA)

-stores and transmits genetic information in modern cells

-A nucleic acid molecule

-usually a double-stranded helix

-each polynucleotide strand consists of nucleotide monomers with a deoxyribose sugar and the nitrogenous bases A T C G

-capable of being replicated and determining the inherited structure of a cell's proteins.

-has the information required for the organism's growth and reproduction

2 Groups of Nitrogenous Bases

1. Purines

-9 atoms (2 rings)

-Adenine (A), Guanine (G)

2. Pyrimidines

-6 atoms (1 ring)

-Cytosine (C), Uracil (U) in RNA, Thymine (T) in DNA

-For every A = amount of G, same with C=T (DNA) and C=U (RNA)

Could chemical evolution produce nucleotides?

-simulations of chemical evolution

-have not yet produced nucleotides

-sugars in nitrogenous bases are easily made

-minerals in deep-sea vents preferentially bind to ribose

-produces a high concentration of ribose

How do nucleic acids form?

-nucleotides polymerize via condensation reactions

Ribonucleic Acid (RNA)

-A type of nucleic acid consisting of nucleotide monomers with a ribose sugar and the nitrogenous bases adenine (A), cytosine (C), guanine (G), and uracil (U)

-usually single-stranded

-functions in protein synthesis

-much more diverse in size, shape, and reactivity than DNA

-Highly versatile

-information-containing molecule

-capable of self-replication

-capable of catalyzing reactions: ribozymes

Purines

Adenine and Guanine

Pyrimidines

Cytosine and Thymine (in DNA) and Uracil (in RNA)

phosphodiester linkage

-"bonds with phosphorus"

-bond occurs with 5' carbon of phosphate group and -OH group on 3' carbon of another

What direction are DNA strands?

-5' > 3' direction

-Phosphate group (5') > Hydroxyl Group (3')

-Reflects the order that nucleotides are added to the growing molecule

Polymerization Requires an Energy Source

-polymerization is catalyzed by enzymes

-energy for polymerization comes from adding two extra phosphate groups to nucleotides

-negatively charged phosphate groups repel each other

-Linking them generates very high energy bonds

-Forms "activated nucleotides"

-Example: Adenosine Triphosphate (ATP)

X-ray crystallography

-a technique used to determine the three-dimensional helical structure of a protein

-Franklin and Wilkins

Antiparallel

The opposite arrangement of the sugar-phosphate backbones in a DNA double helix.

Double Helix

-The form of native DNA, referring to its two adjacent polynucleotide strands wound into a spiral shape.

-sugar-phosphate backbone faces exterior

-nitrogen base pairs face the interior

Complementary base pairing (Watson-Crick Paring)

Hydrogen bonding between particular pyrimidines and purines. Adenine & Thymine. Cytosine & Guanine.

Template Strand

The DNA strand that provides the template for ordering the sequence of nucleotides

DNA grooves

1. Major Groove

2. Minor Groove

Additional Information about DNA

-one turn of helix = 10 base pairs

-hydrophobic interaction cause DNA to twist

-DNA hydrophillic overall

-negatively charged phosphate groups face out

What happens when DNA is too loose of tight?

-It forms supercoils

-wraps around proteins

Compacting DNA allows...

-discrete units for cell division

-helps DNA fit inside nucleus

-contributes to its function

DNA Replication has three steps:

Step 1: Two strands are separated by breaking the hydrogen bonds with heat or enzymes.

Step 2: Free deoxyribonucleotides hydrogen-bond complementary bases on the original strand of DNA (template strand).

-Phosphodiester linkages form to create new strand (complementary strand)

Step 3: Complementary base pairing allows each stand to be copied exactly

-produces two identical daughter molecules

Is DNA a stable structure?

-DNA is very stable

-It is resistant to chemical degradation

- Makes it a reliable store for genetic information

-Stable molecules such as DNA make poor catalysts

-DNA has never been observed to catalyze a reaction

-Biologists think first life form made of RNA

How does the structure of RNA differ from DNA?

1. RNA contains ribose instead of deoxyribose

-2' -OH group on ribose more reactive than -H

-RNA much less stable than DNA

2. RNA contains Uracil instead of Thymine