DNA→RNA → PROTEINSChapters 16 & 17

http://faculty.uca.edu/~johnc/mbi1440.htm

http://www.wappingersschools.org/RCK/staff/teacherhp/johnson/visualvocab/mRNA.gif

1928- GRIFFITH’s EXPERIMENT

Scientists originally thought PROTEINS had to be the genetic material

Images from: http://microvet.arizona.edu/Courses/vsc610/mic205/griffith.jpg

12 A

1943- EXPERIMENTS BY OSWALD AVERY, MACLYN McCARTY, & COLIN MACLEOD

http://www.synapses.co.uk/genetics/dnastruc.html

WITH LIPIDS, POLYSACCHARIDES, OR PROTEINSTHERE’S NO TRANSFORMATION

ONLY NUCLEIC ACIDS CHANGE THE BACTERIA SO . . .

NUCLEIC ACIDS CARRY THEINFORMATION !

1952-Alfred Hershey and Martha Chase

Bacteriophages are viruses that infect bacteria

Phages are made ofDNA surrounded by a protein coat

http://www.mun.ca/biology/scarr/Chase_&_Hershey_1953.jpg

http://oceanworld.tamu.edu/resources/oceanography-book/Images/BacteriophageCartoon.jpg

HERSHEY CHASE BLENDER EXPERIMENT

http://www.mun.ca/biology/scarr/hersheychase-experiment.jpg

http://en.wikipedia.org/wiki/Rosalind_Franklin http://www.time.com/time/time100/scientist/profile/watsoncrick.html

ROSALIND FRANKLIN and MAURICE WILKINS Analyzed DNA with X-ray crystallography to try and determine structure of DNA

1953 - JAMES WATSON & FRANCIS CRICK used Rosalind Franklin’s X-ray crystallography images (PHOTO 51) to come up with alpha helixmodel for the structure of DNA

DOUBLE HELIX

http://www.biosciences.bham.ac.uk/labs/minchin/tutorials/lgdna.html

Linus Pauling's Triple helix model

STRUCTURE OF NUCLEIC ACIDS

Image by: Riedell

Sugar can be DEOXYRIBOSE (DNA) RIBOSE (RNA)

Built from NUCLEOTIDE SUBUNITS

NITROGEN BASES CAN BE:

ADENINEGUANINECYTOSINETHYMINEURACIL

Arrow from: http://www.harrythecat.com/graphics/b/arrow48d.gif

DNA has no URACIL RNA has no THYMINE

PURINES (A & G) have 2 RINGS

PYRIMIDINES (T, C, & U) have 1 RING

http://student.ccbcmd.edu/courses/bio141/lecguide/unit6/genetics/DNA/DNA/fg4.htmlhttp://student.ccbcmd.edu/~gkaiser/biotutorials/dna/fg29.html

Subunits come in as TRIPHOSPHATES

Splitting of nucleotide triphosphates provides the energy to link the nucleotides

See animation

http://www.cat.cc.md.us/~gkaiser/biotutorials/energy/adpan.html

DNA• DOUBLE STRANDED• Strands run

ANTIPARALLEL

• Backbone = sugars and phosphates

• Rungs of ladder = nitrogen bases

• Hydrogen bonds hold sides of ladder together

http://staff.jccc.net/pdecell/proteinsynthesis/antiparralell.gif

RNA• SINGLE STRANDED• Folds into 3D shape

• Backbone = sugars and phosphates

• Rungs of ladder = nitrogen bases

http://tigger.uic.edu/classes/phys/phys461/phys450/ANJUM04/

5’ and 3’ ENDS

• 5’ and 3’ ends named for the CARBON

Erwin Chargaff analyzed DNA from different organisms and found

CHARGAFF’s RULES: A = T G = C

Now know its because:A always bonds with TG always bonds with C

A Purine always bonds to a Pyrimidine

Semi-

Conservative

Conservative

Dispersive

MESELSON & STAHLGrew bacteria for many generations in radioactive

(heavy) 15N . . . so all DNA is heavy

Then grow in 14N, centrifuge as generations divide, and check to see where heavy DNA ends up

Images from: http://instruct1.cit.cornell.edu/courses/biog105/pages/demos/106/unit01/6.dnareplicationmodels.html

http://www.sumanasinc.com/webcontent/animations/content/meselson.html

MESELSON & STAHL

Can tell which model it is by the bandingpatterns of DNA

molecules

SO WHAT ?

http://www.sumanasinc.com/webcontent/animations/content/meselson.html

Proved SEMI-CONSERVATIVE REPLICATION MODEL

Chromosome

E. coli bacterium

Bases on the chromosome

Chromosome Structure in Prokaryotes

© Pearson Education Inc, publishing as Pearson Prentice Hall. All rights reserved

DNA molecule in bacteriasingle circular loop

Approximately 5 million base pairs3,000 genes

CENTRAL DOGMA OF MOLECULAR BIOLOGY

(How information passes in cells)

http://www.emunix.emich.edu/~rwinning/genetics/pics/dogma.jpg

http://student.ccbcmd.edu/~gkaiser/biotutorials/dna/fg12.html

DNA REPLICATION FORK

Starting place = ORIGIN OF REPLICATION

Bacteria have one

Eukaryotes-multiple spots

HOW NUCLEOTIDES ARE ADDED DURING DNA REPLICATION

http://bio.usuhs.mil/biochem4.html

DNA REPLICATION FORK

TELOMERES & TELOMERASE

Image from: AP BIOLOGY by Campbell and Reese 7th edition

Primer removed butcan’t be replaced withDNA because no3’ end available forDNA POLYMERASE

Each replicationshortens DNA strand

• TELOMERES-repetitive sequences added to ends of genes to protect information in code

• TELOMERASE can add to telomere segments in cells that must divide frequently

• Ex: Cells that give rise to sperm & eggs

• Shortening of telomeres may play a role in aging

• Cancer cells may have increased telomerase activity which allows them to keep dividing

http://stemcells.nih.gov/info/scireport/appendixC.asp

ANIMATION

PROOFREADING & REPAIR• Mistakes in final DNA: 1 in 10 billion

• Mistakes in initial base pairing during replication:1 in 100,000

• DNA POLYMERASE proofreads each base as it’s added & fixes errors

• Errors can come from:1. “proofreading mistakes” that are not

caught 2. Environmental damage from CARCINOGENS(Ex: X-rays, UV light, cigarette smoke, etc)

NUCLEOTIDE EXCISION REPAIR• Cells continually monitor DNA and make repairs

• NUCLEASES-DNA cutting enzyme removes errors

• DNA POLYMERASE AND LIGASE can fill in gap and repair using other strand

• Xeroderm pigmentosum- genetic disorder– mutation in DNA enzymes that repair UV damage in skin

cells– can’t go out in sunlight– increased skin cancers/cataracts

DNA →RNATRANSCRIPTION

RNA- the Other Nucleic Acid

Made of NUCLEOTIDESSugar = riboseURACIL NOT THYMINESingle stranded

http://images2.clinicaltools.com/images/gene/dna_versus_rna_reversed.jpg http://tigger.uic.edu/classes/phys/phys461/phys450/ANJUM04

3 KINDS OF RNA HELP WITH INFO TRANSFER FOR PROTEIN SYNTHESIS

RIBOSOMAL RNA (rRNA)Made in nucleolus2 subunits (large & small)Combine with proteins to

form ribosomesBacterial ribosomes different

size than eukaryotic ribosomes• Evidence for ENDOSYMBIOTIC THEORY• Medically significant-some antibiotics target

bacterial ribosomes w/o harming host

rRNA and t-RNA images from Image from: Biology; Miller and Levine; Pearson Education publishing as Prentice Hall; 2006mRNA image from http://wps.prenhall.com/wps/media/tmp/labeling/1140654_dyn.gif

3 KINDS OF RNA HELP WITH INFO TRANSFER FOR PROTEIN SYNTHESIS

TRANSFER RNA (tRNA)

ANTICODON sequence matches CODON on mRNA to add correctamino acids during protein synthesis

AMINOACYL-tRNA SYNTHETASE Enzyme attaches a specific amino acid using energy from ATP

http://www-math.mit.edu/~lippert/18.417/lectures/01_Intro/

3 KINDS OF RNA HELP WITH INFO TRANSFER FOR PROTEIN SYNTHESIS

MESSENGER RNA (mRNA)carries code from DNA to ribosomes

TRANSCRIPTION

See a video clip aboutTRANSCRIPTION

• Prokaryotes- mRNA functional as soon as transcribed

• Eukarytoes-mRNA is processed before use

Image from AP BIOLOBY by Campbell and Reese

SEE PROCESSING VIDEO

mRNA’s require EDITING before use

• Message in NOT CONTINUOUS

• INTRONS are removed

Image by Riedell

mRNA EDITING

snRNPs (small nuclear ribonucleoproteins)

Made of proteins and RNA

Role in the SPLICEOSOME

(Complex that cuts out the

INTRONS and joins EXONS

to make the final mRNA)

RIBOZYMES-RNA molecules that function as enzymes (pre-RNA can remove its own introns)

INTRONS & EXONS

• PROTEIN DOMAINS• Modular• Ex:

– Active site,– site to attach to membrane

• In many proteins, different exons code for different domains

• May facilitate evolution of new proteins

(EXON SHUFFLING)• Increased Crossing over• Mix & match exons

Image from AP BIOLOGY by Campbell and Reese

GTP "cap" put on 5’ end- stability and used to bind mRNA to ribosome

• PolyA "tail" put on 3’ end (AAA)- stability and movement through the nuclear membrane

Image from AP BIOLOBY by Campbell and Reese

TRANSLATION(Protein synthesis)

Section 12-3 64 possible codons

Code is REDUNDANT“WOBBLES”

Some amino acidshave more than onecodon.

START=AUG(Methionine is 1st)3 codons for STOP

Image from: Biology; Miller and Levine; Pearson Education publishing as Prentice Hall; 2006

http://www.biologycorner.com/bio4/notes/codon.html

 TranslationSection 12-3

Image from: Biology; Miller and Levine; Pearson Education publishing as Prentice Hall; 2006

Figure 12–18 Translation (continued)Section 12-3

Image from: Biology; Miller and Levine; Pearson Education publishing as Prentice Hall; 2006

TRANSLATION

SEE ANOTHERTranslation Animation

How translation works

REGULATION & MODIFICATIONDURING TRANSCRIPTION• Proteins affect ability of RNA polymerase to bind to DNA

AFTER TRANSCRIPTION• Speed of editing introns/exons• access to transport proteins or speed of transport out • Control amount of mRNA degradation by RIBONUCLEASES

DURING TRANSLATION• Polyribosomes (polysomes)• Availability of enzymes

• POST-TRANSLATIONAL MODIFICATION• Alter protein (add phosphates, sugars, etc)• Cut and join peptide chains

COMPLETING PROTEINS• POLYRIBOSOMES (POLYSOMES)

– Numerous ribosomes translate same mRNA at same time

– 3-D folding (1’, 2’, 3’ structure)– Chaparonins

POST-TRANSLATIONAL MODIFICATIONS– Some amino acids modified by addition of

sugars, lipids, phosphate groups, etc– Enzymes can modify ends, cleave into pieces

join polypeptide strands (4’ structure)

Ex: Made as proinsulin then cut

Final insulin hormonemade of two chains connected by disulfide bridges

http://www.vivo.colostate.edu/hbooks/pathphys/endocrine/pancreas/insulin.html

• 1st to suggest genes dictate phenotypes through enzymes that catalyze specific chemical reactions

• Postulated that the symptoms of an inherited disease are due to inability to make a specific enzyme

• Coined term “inborn errors of metabolism” to describe such diseases• Beginning of “One gene-one enzyme” hypothesis• ALCAPTONURIA- “black urine” disease- defect in enzyme that breaks down

amino acid tyrosinehttp://www.personal.psu.edu/faculty/w/x/wxm15/Online/Molecular%20Biology/media/phenylalanine.gifhttp://www.nature.com/bjp/journal/v147/n1s/images/0706466f5.jpg

ARCHIBALD GARROD1902

Mutations • Point mutations

– single base change– base-pair substitution

• silent mutation– no amino acid change– redundancy in code

• missense– change amino acid

• nonsense– change to stop codon

Slide from Explore Biology by Kim Foglia

Point mutation leads to Sickle cell anemia

What kind of mutation?

Slide from Explore Biology by Kim Foglia

Sickle cell anemia

Slide from Explore Biology by Kim Foglia

Mutations • Frameshift

– shift in the reading frame

• changes everything “downstream”

– insertions• adding base(s)

– deletions• losing base(s)

– More damaging atbeginning of gene than at end

Slide modified from: Explore Biology by Kim Foglia

XERODERMA PIGMENTOSUM• UV light damage causes

THYMINE DIMERS• Usually repaired

(Nucleotide Excision repair)– Repair enzymes defective– Increased skin cancer– severe burns in sunlight– Must avoid sunlight

AP BIOLOGY by Campbell and Reese

http://www.shadeshort.com/

DNA → DNA ____________

DNA → RNA ____________

RNA→ Protein ___________

REPLICATION

TRANSCRIPTION

TRANSLATION