© 2003 mark s. davis chapter 21 nucleic acids. © 2003 mark s. davis queen victoria hemophilia

© 2003 Mark S. Davis

Chapter 21

Nucleic Acids


Queen Victoria

• Hemophilia

•


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


Chromosomes• Humans have 46

–

• Germ cells have 23– –

• Contain all genetic information of the organism

•


RNA

• Leave nucleus

•


Nucleotides

• Monomers that make up DNA and RNA

•


Nucleotides

• Made from–


Naming• Sugar and base

–Adenine + sugar =

–Cytosine + sugar =

• is second part of the name

• dGMP


5’ – 3’ Phosphodiester

• In making DNA –

• This is the direction used for naming


DNA Structure

• Watson and Crick 1953

•

• Complementary pairs–


Complementary Strands

• Bases located

• Maximum

• Maximum

• Hydrophobic bonds to the bases above and below


Given…

• G A T T A C A

• What is the complementary strand?


Size of DNA

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


RNA

• Single strand

• Different types–


RNA Pairing•

•

• Only about ½ molecules base pair

• Acceptor stem:

• Anticodon -


Information flow

• Replication:

• Transcription:

• Translation:


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


DNA Polymerase

•

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

•


Practice

• What is the corresponding daughter strand to the parent –


Transcription

• Transcription bubble

• RNA Polymerase acts on the template strand only

• There is a start site

• There is a termination site


RNA Polymerase

• No proofreading function

• Error

• Initial RNA is called primary transcript RNA, ptRNA

• Later modified to the other types


What RNA is formed?

• If the DNA sequence is:

• What is the RNA that is synthesized?


Post transcription

• End capping–

• Base modification

• Splicing–


Translation• Protein synthesis

– –

• Sequence of bases specifies amino acid sequence–

• 64 codons for 20 amino acids–


Translation• Each tRNA carries ONLY ONE aa

• Aminoacyl-tRNA synthetase–

• Peptidyl transferase–

• Synthesis terminates when STOP codon is reached


Posttranslational Processing

• Most lose

• Folding begins

• Disulfide-bridging

• Quaternary structures assembled


Control at every step

• Not every cell expresses every gene

• Specialized

• Repressor proteins–

• Inducer proteins–


Mutations• Error in base sequence

– – –

• Substitution (point) mutations–

• Frameshift mutations–


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


Spontaneous Mutations and Mutagens

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

burnt meats

• Radiation–


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


Mutations

• Somatic cells–

• Germ cells– –


Antibiotics

• Chemicals to fight infection

• Block protein synthesis – –

• Must finish whole course

• Bacteria

• Antibiotic resistant bacteria


Viruses

• DNA or RNA with protein coat

• No functions outside cell

• Enter cell and “hijack” it

• Each virus attacks only specific cells– TMV– AIDS


DNA Viruses

• Enter host cell and nucleus

• Insert themselves into

• Hiding inside cell – hard for immune system to detect

• Can stay indefinitely


RNA Viruses

• Enters cell

• Directs synthesis of

• Uses machinery of host to make copies of itself


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


Treatment

• Antibiotics don’t work

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

• Best method:


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


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


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


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


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/


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


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


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?


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

© 2003 mark s. davis chapter 21 nucleic acids. © 2003 mark s. davis queen victoria hemophilia

Documents

rna slide

dna slide

davis replication

naming slide

davis goals

davis practice

davis control

davis chapter