© 2003 Mark S. Davis Chapter 21 Nucleic Acids. © 2003 Mark S. Davis Queen Victoria Hemophilia

© 2003 Mark S. Davis

Chapter 21

Nucleic Acids

© 2003 Mark S. Davis

Queen Victoria

• Hemophilia

•

© 2003 Mark S. Davis

Goals

• Describe nucleotides, RNA and DNA, polypeptides

• Know the 3D structure of nucleic acids

• Describe mutations and their effects

• Describe viruses and Recombinant DNA technology

© 2003 Mark S. Davis

Chromosomes• Humans have 46

–

• Germ cells have 23– –

• Contain all genetic information of the organism

•

© 2003 Mark S. Davis

RNA

• Leave nucleus

•

© 2003 Mark S. Davis

Nucleotides

• Monomers that make up DNA and RNA

•

© 2003 Mark S. Davis

Nucleotides

• Made from–

© 2003 Mark S. Davis

Naming• Sugar and base

–Adenine + sugar =

–Cytosine + sugar =

• is second part of the name

• dGMP

© 2003 Mark S. Davis

5’ – 3’ Phosphodiester

• In making DNA –

• This is the direction used for naming

© 2003 Mark S. Davis

DNA Structure

• Watson and Crick 1953

•

• Complementary pairs–

© 2003 Mark S. Davis

Complementary Strands

• Bases located

• Maximum

• Maximum

• Hydrophobic bonds to the bases above and below

© 2003 Mark S. Davis

Given…

• G A T T A C A

• What is the complementary strand?

© 2003 Mark S. Davis

Size of DNA

• 3x109 base pairs• • • Organized around • Around 200 base pairs/

© 2003 Mark S. Davis

RNA

• Single strand

• Different types–

© 2003 Mark S. Davis

RNA Pairing•

•

• Only about ½ molecules base pair

• Acceptor stem:

• Anticodon -

© 2003 Mark S. Davis

Information flow

• Replication:

• Transcription:

• Translation:

© 2003 Mark S. Davis

Replication

• Copy all 46 chromosomes in less than a day (about 8 hrs)

• Error – • Always in 5’ 3’ direction and two

strands grow opposite• DNA

© 2003 Mark S. Davis

DNA Polymerase

•

• “Checks” the accuracy of the pairing and correcting errors

•

© 2003 Mark S. Davis

Practice

• What is the corresponding daughter strand to the parent –

© 2003 Mark S. Davis

Transcription

• Transcription bubble

• RNA Polymerase acts on the template strand only

• There is a start site

• There is a termination site

© 2003 Mark S. Davis

RNA Polymerase

• No proofreading function

• Error

• Initial RNA is called primary transcript RNA, ptRNA

• Later modified to the other types

© 2003 Mark S. Davis

What RNA is formed?

• If the DNA sequence is:

• What is the RNA that is synthesized?

© 2003 Mark S. Davis

Post transcription

• End capping–

• Base modification

• Splicing–

© 2003 Mark S. Davis

Translation• Protein synthesis

– –

• Sequence of bases specifies amino acid sequence–

• 64 codons for 20 amino acids–

© 2003 Mark S. Davis

Translation• Each tRNA carries ONLY ONE aa

• Aminoacyl-tRNA synthetase–

• Peptidyl transferase–

• Synthesis terminates when STOP codon is reached

© 2003 Mark S. Davis

Posttranslational Processing

• Most lose

• Folding begins

• Disulfide-bridging

• Quaternary structures assembled

© 2003 Mark S. Davis

Control at every step

• Not every cell expresses every gene

• Specialized

• Repressor proteins–

• Inducer proteins–

© 2003 Mark S. Davis

Mutations• Error in base sequence

– – –

• Substitution (point) mutations–

• Frameshift mutations–

© 2003 Mark S. Davis

Spontaneous Mutations and Mutagens

• Spontaneous mutations–

• Sodium nitrite– In processed meats– Converts cytosine to uracil– Overall danger thought to be low– Reduces occurrence of botulism

© 2003 Mark S. Davis

Spontaneous Mutations and Mutagens

• Benzopyrene– – Found in car exhaust, tobacco smoke,

burnt meats

• Radiation–

© 2003 Mark S. Davis

Silent Mutations

• Base-sequence errors that don’t affect organism– 64 codons for 20 amino acids– – Change may be in unimportant region– – Genes have 2 or more copies

© 2003 Mark S. Davis

Mutations

• Somatic cells–

• Germ cells– –

© 2003 Mark S. Davis

Antibiotics

• Chemicals to fight infection

• Block protein synthesis – –

• Must finish whole course

• Bacteria

• Antibiotic resistant bacteria

© 2003 Mark S. Davis

Viruses

• DNA or RNA with protein coat

• No functions outside cell

• Enter cell and “hijack” it

• Each virus attacks only specific cells– TMV– AIDS

© 2003 Mark S. Davis

DNA Viruses

• Enter host cell and nucleus

• Insert themselves into

• Hiding inside cell – hard for immune system to detect

• Can stay indefinitely

© 2003 Mark S. Davis

RNA Viruses

• Enters cell

• Directs synthesis of

• Uses machinery of host to make copies of itself

© 2003 Mark S. Davis

Retroviruses

• Special RNA virus

• Enters cell and directs synthesis of viral DNA using reverse transcriptase

• DNA inserts into host genome

• Can hide or remain dormant for long periods of time– HIV

© 2003 Mark S. Davis

Treatment

• Antibiotics don’t work

• Body doesn’t recognize virus once hiding in host cell

• Best method:

© 2003 Mark S. Davis

Recombinant DNA Technology

• Began in mid-70s

• Transplanting or altering of DNA

• Benefits– Therapeutic drugs– Improvements to crops and herds– Curing/treating of genetic diseases

© 2003 Mark S. Davis

Production of human insulin

• First application of recombinant DNA technology

• Uses yeast and bacteria as vehicle– Bacteria have genomic DNA and a

plasmid

• Less side effects than cow or pig insulin

© 2003 Mark S. Davis

ProcessIdentify gene encoding wanted protein

1. Isolate this gene from the donor DNA

2. Splice into plasmid (vector DNA)1. Restriction enzymes

3. Recombinant DNA (new plasmid) back into E. coli

1. Chemical shock

2. Heat shock

© 2003 Mark S. Davis

Other techniques• Microinjections

– Direct injection of DNA into nucleus of another cell

– Cloning ~~~ Dolly

• Viral vectors– Altered virus (usually retrovirus)– Carries new DNA to host cell– Research now for cystic fibrosis

© 2003 Mark S. Davis

A Little More About Cloning• Enucleation of cell:

– http://gslc.genetics.utah.edu/units/cloning/whatiscloning/images/enucleation.mpg

• Nuclear Transfer:– http://gslc.genetics.utah.edu/units/cloning/

whatiscloning/images/transfer.mpg

• Cloning “Practice”:– http://gslc.genetics.utah.edu/units/cloning/c

lickandclone/

© 2003 Mark S. Davis

Transgenic Breeding

• Organisms with altered DNA

• Grow faster, larger, etc.

• Resistant to pests– http://www.pbs.org/wgbh/harvest/engineer/t

ransgen.html

• Many already in your supermarket

© 2003 Mark S. Davis

Gene Therapy

• Human Genome Project– Finished with sequence– Now identify genes and proteins

• Insert correct gene for defective one• Modified adenovirus (common cold)

– Aerosol spray inhaled– Injection into bloodstream– Incubation of cells

© 2003 Mark S. Davis

Ethical Considerations• Effects of recombinant DNA?

• Can we test people for diseases?– Alzheimer’s; Huntington’s

• Gene Therapy– Enhance intelligence, strength– Pick eye color

• Who will benefit? Will anyone suffer?

© 2003 Mark S. Davis

Internet Sites of Interest

• PBS Site about GMOs– http://www.pbs.org/wgbh/harvest/

• Genetic Science Learning Center– http://www.pbs.org/wgbh/harvest/

• NWABR– http://www.nwabr.org