Structure and Function of DNA

Ch. 13

DNA

• Encodes hereditary information.• Located in the nucleus of a eukaryotic cell.• Each chromosome is a macromolecule of DNA.• All living things have DNA and use the same code!• Shape is double helix.

Discovery of DNA

• Early 1900s scientists knew chromosomes carry hereditary info chromosomes made of DNA and protein

But which substance was source of genetic info?

Nucleotides

• Subunits (monomers) of DNA = nucleotides

• 3 parts of nucleotides: Nitrogenous base Phosphate group sugar

Four nitrogen bases: A,T,C,G

Purines:AdenineGuanine

Pyrimidines:ThymineCytosine

Base Pairs

• Always A – T• Always C - G

• Purines = double carbon rings• Pyrimidines = single carbon rings

James Watson and Francis Crick

• Watson (American) worked with Crick (English) at Cambridge, England to discover the double helical structure of DNA Two outside strands of P and sugar cytosine = guanine (3 bonds) adenine = thymine (2 bonds) Discovery of DNA Structure

Maurice Wilkins and Rosalind Franklin

• Rosalind Franklin's contribution

Double Helix

• The sugar/phosphate make the backbone

• Nitrogen bases are the rungs

• Ladder twisted to form double helix

http://www.biotechnologyonline.gov.au/images/contentpages/helix.jpg

• Order of the bases gives the code for proteins.

http://newsimg.bbc.co.uk/media/images/38889000/gif/_38889947_dna_mouse2_203.gif

• Antiparallel- each side facing opposite direction

DNA Visualizations

3D structure of DNA

Molecular Visualizations of DNA

James Watson on DNA

DNA Replication

DNA structure

DNA Replication (S phase)

http://classes.midlandstech.edu/carterp/Courses/bio225/chap08/08-03_DNAReplication_1.jpg

DNA replication:

Helicase enzyme uncoils DNA

New complementary strand made, corresponds to bases on each original strand.

(A-T) (C-G)

Semiconservative = 1 new strand + 1 old

See p. 301 in Holt textbook!http://www.contexo.info/DNA_Basics/images/dna_replicationHGPweb.gif

DNA replication animation

• DNA Replication visualization

• DNA replication (6/10)

• DNA replication short

• DNA Replication• DNA replication Crash Course

Protein Synthesis

The Human Genome Overview of Protein Synthesis

DNA

http://www.biologie.uni-hamburg.de/b-online/library/bio201/trinity.gif

Overview of protein synthesis

http://www.scq.ubc.ca/wp-content/translation_01.gif

Amino Acids:

• Subunits of protein are called amino acids• Only 20 amino acids (a.a.) in all life• Amino acids link together make different

proteins.

Three bases code for 1 amino acid

http://www.brooklyn.cuny.edu/bc/ahp/BioInfo/graphics/GP.GeneticCode.GIF

Compare DNA and RNA

• DNA RNA• Deoxyribonucleic acid Ribonucleic acid• Deoxyribose (sugar) ribose (sugar)• A, C, G, T A, C, G, U (uracil)• double stranded single stranded• stays in nucleus can move out of

the nucleus

Three types of RNA:

Messenger RNA = mRNA

Transfer RNA = tRNA

Ribosomal RNA = rRNA

Making proteins

1. DNA is transcribed into mRNA in nucleus (transcription)

2. mRNA leaves nucleus and bonds to rRNA on ribosome in cytoplasm.

3. mRNA is then translated into proteins by ribosome. (translation)

4. tRNA brings in amino acids to be bonded together to make protein.

DNA transcription and protein synthesis

Transcription

• Copy DNA code into mRNA in nucleus.

Uracil replaces thymine in RNA.(A-U)

mRNA leaves nucleus and finds a ribosome in cytoplasm

http://www.scientificpsychic.com/fitness/transcription.gif

Translation

• mRNA takes info to cytoplasm and bind to ribosome

• tRNA brings in amino acid & matches codon

• A.A. are linked to make protein.

https://eapbiofield.wikispaces.com/file/view/translation.gif

Translation

Codon = 3 letter mRNA code

for one amino acid

http://library.thinkquest.org/C0123260/basic%20knowledge/images/basic%20knowledge/RNA/genetic%20code.jpg

DNA Visualizations

Molecular Visualizations of DNA

Overview of protein synthesis

http://www.scq.ubc.ca/wp-content/translation_01.gif

DNA – The original drawing

RNA – Copies or blueprints

Amino Acid chain (protein) – the finished, functional product of a gene

Central Dogma

DNA RNA Proteins

Gene Regulation:

• Ability of organism to control which and when genes are expressed (translated)

When things go wrong…

• Are mutations heritable?

• Are mutations beneficial/harmful/both?

• Are mutations the cause of evolution?

• What are mutations?

• Find the base pairs that are incorrect in this strand of DNA.

G G A T A T T A C C G T T G A A A G C A T

C C G A T G A T G C C A A C T G G C G C A

• Find the base pairs that are incorrect in this strand of DNA.

G G A T A T T A C C G T T G A A A G C A TC C G A T G A T G C C A A C T G G C G C A ↑ ↑ ↑ ↑ ↑ ↑

Genetic MUTATION

• A change in the nucleotide sequence of a gene.

• ACU vs. AGU

SUBSTITUTION

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Sickle Cell

Single nucleotide substitution

Ex: in sickle cell disease, valine is substituted for glutamate (GUA for GAA)

http://carnegiescience.edu/first_light_case/horn/lessons/images/hemoglobins.GIF

DELETION

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Ex: cystic fibrosis

Cystic Fibrosis CTFR transmembrane protein

Most common CF cause is deletion of 3 base pairs for phenyalanine

http://www.largeglassdesign.com/nutrition/images/stories/cf/lung_affects.png

Normal CFTR Sequence:Nucleotide ATC ATC TTT GGT GTTAmino Acid Ile Ile Phe Gly Val

F508 CFTR Sequence:Nucleotide ATC ATT GGT GTTAmino Acid Ile Ile Gly Val

INSERTION

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Ex: Crohn’s disease

FRAMESHIFT MUTATIONS

• Insertion or deletion changes the reading frame:

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• Now you’re making a completely different amino acid sequence!

DUPLICATION

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MUTAGENS

• Substances like chemicals and radiation that can damage DNA

Which mutations can be passed to offspring?

• Somatic or sex-cell mutations?

• Why?

Chromosome mutations

• Pieces of DNA can be deleted or moved to a different location on the chromosome or to another chromosome.