bioed online the molecular basis of heredity: structures and functions of nucleic acids by raye l....

BioEd Online

The Molecular Basis of Heredity:

Structures and Functions

of Nucleic Acids

by Raye L. Alford, PhD

Baylor College of Medicine

DNA Model by J. Watson and F. Crick© Cold Spring Harbor Laboratory Archives

www.BioEdOnline.orgBioEd Online

The Atomic Components of DNA and RNA

Carbon (C)

Hydrogen (H)

Nitrogen (N)

Oxygen (O)

Phosphorus (P)

Thomas Jefferson National Accelerator Facility, Office of Science Education

The Periodic Table of Elements


The Molecular Components of DNA and RNA (I)

Bases DNA and RNA

Adenine (A) Cytosine (C) Guanine (G)

DNA Only Thymine (T)

RNA Only Uracil (U)

2005 VisiScience Corporation. All Rights Reserved.

Uracil

ThymineGuanine

Adenine Cytosine


The Molecular Components of DNA and RNA (II)

The Sugar – Phosphate Backbone DNA – Deoxyribose (Pentose) Sugar RNA – Ribose (Pentose) Sugar Phosphate Group

Base + Sugar + Phosphate = Nucleotide

Deoxyribose + Triphosphate Group Ribose + Triphosphate Group

BASE BASE

1’

2’3’

5’1’

2’3’

5’

2005 VisiScience Corporation All Rights Reserved


The DNA and RNA Strand

Nucleotide + Nucleotide(n)

= DNA (or RNA) strand

Deoxyribonucleotides = DNA

Ribonucleotides = RNA


3'

5'

Base

Base

Base

1'

3'

5'


5'

5'

3'

3'

DNA is Double-Stranded

Hydrogen bonds enable the DNA ladder.

A always pairs with T. C always pairs with G.

The sequence of one strand predicts the sequence of the other.


3

45

21

4

5

1

6

32

87

96

Thymidine

Two Hydrogen Bonds

Adenosine

93

45

2

4

5

1

6

32

7

6

1

8Cytidine

Guanosine

Three Hydrogen Bonds


The DNA Double Helix

The DNA ladder spirals in a double helix.

There are 10 base pairs per turn.

Each turn is 34 Angstroms high.

The helix is 24 Angstroms wide.

The major groove is the wider of the two grooves.

The other groove is called the minor groove

Redrawn from National Institute of Medical Sciences, NIH

Major groove

Minor groove

Major groove

Minor groove


DNA Replication

Replication relies on complementary base pairing.

Replication occurs before Mitosis and Meiosis I.

DNA replication is semi-conservative.

DNA is synthesized by DNA polymerase.

DNA is synthesized in a 5’ to 3’ direction. 5‘

5'

3'

3'

5'

Redrawn from National Center for Biotechnology Information

3'

5' 3'

5'


Transcription

Like replication, transcription relies on base pairing. Instead of DNA, RNA is made.

RNA is synthesized by RNA polymerase II.

3'

3'

5'

NascentRNA

TemplateStrand

5'

5' 3'

CodingStrand

ElongationSiteRNA Polymerase

Unwinding

Rewinding

Movement of polymerase

2005 VisiScience Corporation. All Rights Reserved


RNA Processing in Eukaryotic Cells

Splicing out of introns,capping with 5' methyl cap,polyadenylation

Exon5' 3'

Intron

RNA

IntronExon Exon

mRNAAAAAAAAn



Translation Ribosomes make proteins from the messages encoded in

mRNA. Three nucleotide groups called codons encode one

amino acid. This is the genetic code.

Adapted from: L. Stryer. Biochemistry, 3rd ed..

5' 3'

Nearly completed protein

Ribosome

Beginning of protein

mRNA


The Genetic Code

Each 3-nucleotide mRNA codon specifies a particular amino acid.

Each tRNA transfers a particular amino acid.

To use the chart, read from the mRNA.

National Center for Biotechnology Information, National Library of Medicine, NIH

MET-tRNA

codon codon codon

mRNA

anticodon loop


Summary of DNA

DNA: is a complex macromolecule

made of several basic atomic components.

encodes genes, the instructions needed to make RNA and proteins.

is a double helix. The complementary nature of the DNA helix permits its replication and transcription.

is transcribed into RNA.2005 VisiScience Corporation. All Rights Reserved.


Summary of RNA

mRNA (messenger RNA) is the template for the production of proteins, the molecules that build and comprise structures and perform enzymatic reactions.

tRNA (transfer RNA) enables the transfer of amino acids into a growing polypeptide chain.

rRNA (ribosomal RNA) is a component of protein-producing ribosomes.

bioed online the molecular basis of heredity: structures and functions of nucleic acids by raye l....

Documents

dna helix

dna polymerase

bioed online rna processing

rna adenine

dna ribonucleotides

rna strand nucleotide

dna double helix

bioed online transcription