Leuture 5 DNA discovery and structure

What is the Biological Function

Gregor Mendel (1822-1884) revealed that….

heredity is the result of discrete units of inheritance.

* Traits are not blended - can either have mom or Dad traits can be pasted down generation from generation

Wilhelm Ludvig Johannsen coined the term gene to refer the …

not or particle of inheritance

• Phenotype - Trait expressed by gene

• Genotype - collection of genes that code for phenotype

Archibald Garred

Identifies alkaptonuria as a heritable geneticc disease that follows Mendel’s law

Alkaptonuria

* black urine - inborn error of metabolism used of pedigree

What is the Biochemical basis of hereditary?

Majority of death resulted from secondary infections of…

Streptococcus pneumoniae

What are the two strains of streptococcus pneumoniae

• Rough Colony (R)

• Smooth Colony (S)

What is the R strain

benign (lacks a protective capsule, recognized and destroyed by host’s immune system)

S-strain

Is virulent (polysaccharide capsule prevents detection by host’ immune system)

Fredirck Griffith (1928) discovered that the ..

dead virulent strain of S. pneumonia (S-strain) could transform the harmless form (R-strain) into the virulent form.

Avery, and McCarty and Mcleod discovered that…

R-strains could be transformed with DNA extracts from dead S-strains

Conclusion

the molecule that carries the heritable information is DNA

Bacteriophage are?

They consist of two component

• Class of Viruses that infect bacteria

• Requires bacterial host for replication

• DNA Genome

• Protein Capsid

Bacteriophage life cycle

The genetic information required for viral replication must be contained in either the DNA or the proteins

Hershey and chase (1952)

Labeled Bacteriophage with radioactive elements

• Phosphorous of DNA

• The sulfur of Amino Acids - Cysteine and methionine

• Traced the transfer of those elements to the infected bacteria

Hershey and Chase confirmed What?

Experiment DNA and Protein/sulfur put in viruses that allowed to infect E.coil- blender shear off viral heads off bacter- infected bacteria contained 35P not S35

Nucleotides

A nucleotide consist of a nitrogen-containing base, a five-carbon sugar, and one or more phosphate groups

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Carbons of the deoxyribonucleotide (monomer unit of DNA)

1’

Base attached

2’

Deoxygenated in DNA

3’

OH - forms phosphodiester bond

5’

Phosphate group attached

What are the Nucleotide bases

What are Pyrimidine and Purine bases

DNA Polymerization

• Hydrolysis of Phosphor anhydride bond provide energy

• Creates favorable reaction - high energy → Low energy

Erwin Chargaff do?

Nucleotide occur in predictable ratios in living things

What is Chargaff's Rule?

A = T

G = C

Discovery of the structure of DNA - Watson, Crick, Wilkins, and Franklin

Discovery of structure of DNA - Watson, Crick, Franklin, and Wilkins

• Double helix with Bases pointing inward

• Complementary base-pairing between purine and pyrimidine explain Chargaff’s rule

Complementary base-pairing of DNA makes it possible to faithfully replicate of genetic material

* Each strand serves as a template to make a new double helix - semi-conservative replication.

Part 2 - DNA and Chromatin Structure

DNA Structure backbone is assembled via condensation reactions forming…

Phosphodiester bonds

Nucleotides are connected 5’ to 3’ and strands are..

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one strand and the other…

• antiparallel

• One strand runs 5’ to 3’

• Other runs 3’ to 5’

DNA Structure is held together by…

Hydrogen bonds between bases

G to C bonds are… than A to T

Stronger

Increasing the GC content increases the … of DNA

Stability

The DNA Helix has two grooves

• Major groove - 22 A wide - primary site of sequence specific binding of protein

• Minor groove - 12 A wide - primary non-specific binding of proteins

Major DNA sequence features (2)

• Genome

• Gene

Genome?

The complete DNA sequence of an organism

Gene

Portion of the genome transcribed to RNA and usually translated into a protein

Genes are read (transcribed) …..from either strand of the double helix

5’ to 3’

Replication Origin

Special sequence where the replication of DNA begins

Centromere

A special sequence that attaches to mitotic spindle and allows chromosome separation in mitosis

Telomere

Repetitive sequences at the ends of Chromosomes that protect from degradation and/or fusion with other chromosomes

The Problem with DNA is that it’s Thin and Extremely long molecule.

* Each cell in your body has 2 meters of DNA

How does DNA fit in the cell?

DNA is packed with proteins into a complex called chromatin

Histone proteins are major elements of…

chromatin

Histone protein come together in an …. complex which DNA wraps around.

Octomer

Nucleosome?

The histone + DNA Complex

Histones proteins are…. charged and attract the …. charged DNA

Positively charged

Negatively charged

Decondense Chromatin appears like …..

DNA wraps around nucleosome ….times …bp

Beads on a string

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1\.7 times (147 basepairs)

Another histone protein…. can …

H1 can link histones together and help condense the chromatin fibers

Chromatin fibers are … into loops by …

Folded

CTFC proteins

What do CTFC do?

Pull loop through until it reaches a specific sequence

• Matches Specific DNA Sequences

• Chromosome loop-forming clamp proteins

What is the Result of this?

Each DNA molecule has been packaged into a Mitotic chromosome that is 10,000-fold shorter than its fully extended length

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* Fully condense at Meta-phase of cell cycle

DNA in Eukaryote cells is organized into ..

Chromosomes

What is a chromosome

Complex of DNA (One continuous helix) and many proteins

In human chromosomes are paired …

Homologous chromosomes, one from each parent

Chromosomes take on different conformations through the cell cycle

Interphase, meta phase, interphase

In interphase, when cell is not dividing,..

different chromosomes reside in distinct territories within the nucleus.

Nucleus chromatin is found in two forms

• Heterochromatin

• Euchromatin

Heterochromatin

That is condensed and not transcriptionally active by telomere and centromere.

Euchromatin

That is loose and transcriptionally active

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Chromatin conformation and composition is dynamic and modified for specific biological function

Chromatin remodeling complex (3)

• Positions nucleosomes

• Condenses and decondense

• Requires ATP

The Histone proteins have….terminal tails that are…

N-terminal tails that are modified to mark regions of genome for transcriptional activation or silencing

What are the 5 Levels of DNA

1. Double helix

2. Beads on a string - DNA wraps around Histone 1.7 times 147bp creating nucleosome

3. Chromatin fibers are made with Histone HI

4. Chromatin fiber loops with CTFC - pull loop through until it reaches a specific sequence

5. Folded loops are fully condensed at meta-phase of cell cycle