lecture 5 - dna

8/10/2019 Lecture 5 - DNA

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Biol200 - Concepts in Biology 1

Reminders:

Project 1, Part 4 due Monday 6/9

Project 2, Part 1 due Monday 6/9


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Figure 1 The rate of transport of molecule X was determined in HeLa and HEK cells overincreasing concentrations of X. The experiment was repeated 5 times for each concentrationtested. The star indicates a significant difference in rate of transport at a p0.001.

1. What are the independent and dependent variables in this experiment?a. Independent = Rate of Transport, Dependent = Cell Type (HeLa or HEK)b. Independent = Cell Type (HeLa or HEK), Dependent = Concentration of Xc. Independent = Concentration of X, Dependent = Rate of Transportd. Dependent = Rate of Transport, Independent = Cell Type (HeLa or HEK)


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Figure 1 The rate of transport of molecule X was determined in HeLa and HEK cells overincreasing concentrations of X. The experiment was repeated 5 times for each concentrationtested. The star indicates a significant difference in rate of transport at a p0.001.

2. What conclusions can we draw from this data set?a. We can conclude that the maximal rate of transport of X is higher in HEK cells than in

HeLa cells.b. We can conclude that rate of transport of X is impaired at higher concentrations of X.c. We can conclude that at concentrations of X less than 2, HeLa cells transport X at a

significantly higher rate than the HEK cells.d. We can conclude that while the rate of transport of X is significantly impaired in HeLa

cells at concentrations of 0.5 and 1, the maximal rate appears equal for both cell types.


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Structure of Genetic Material

Goals:

Review the structural characteristicsof nucleotides (DNA/RNA) Review how that structure can be

taken advantage of to form polymers

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Biol200 - Concepts in Biology 6Structure of Genetic Material

a) The threecomponents of anucleotide includethe phosphate andsugar groups and anitrogenous base.

a) Phosphate units linkto sugar units,formingphosphodiesterbonds that make upthe backbone of apolynucleotidemolecule.

DNA is composed of a series of smaller molecules called nucleotides.


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Figure 3: All polynucleotides contain an alternatingsugar-phosphate backbone. This backbone isformed when the 3' end (dark gray) of onenucleotide attaches to the 5' phosphate end (lightgray) of an adjacent nucleotide by way of aphosphodiester bond.


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ribose

DNA RNA


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Nucleotide bases are classified into purines and pyrimidines.

A pyrimidine is a four-carbon ring connected bynitrogen atoms at the 1and 3 positions.

The pyrimidines cytosine(C) and thymine (T) arefound in DNA, andcytosine and uracil (U) arefound in RNA.

A purine molecule is apyrimidine ring connectedto an imidazole ring; theoverall structure is adouble ring.

Adenine (A) and guanine(G) are the purines in bothDNA and RNA.



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Chargaffs Second Rule: Guanine can pair only with cytosine,using three hydrogen bonds, and

adenine can pair only with thymine,using two hydrogen bonds. These arethe base pairing rules of the DNAdouble helix. (Note that thymine isreplaced by uracil in RNA).

The directionality of the sugar-phosphate backbone results in onestrand running opposite to the other.


G CA T (U)


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Figure 4: Double-stranded DNA consists of two polynucleotide chains whosenitrogenous bases are connected by hydrogen bonds. Within this arrangement,each strand mirrors the other as a result of the anti-parallel orientation of thesugar-phosphate backbones, as well as the complementary nature of the A-T andC-G base pairing.


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Maurice Wilkins

data Rosalind Franklin

s data

X-ray Diffraction of DNA



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Watson and Crick DNA Model



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Watson and Crick DNA Model



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The DNA double helix features two

polynucleotide strands with sugar-phosphate backbones linked bypurine-pyrimidine pairs.

The secondary structure of DNA is adouble helix: two intertwined strands ofDNA.

The double helix structure of DNA ismade up of a phosphate-sugarbackbone with paired nucleotide bases

on the interior of the molecule. The only pairs of nucleotide bases in

DNA are between purines andpyrimidines.

DNA and RNA form complex secondary structures.



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If 26% of the bases in a piece of double-stranded DNA is G, what percent of thebases are T in that same DNA piece?

A. 13%

B. 24%

C. 26%

D. 48%

E. None of the above



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Figure 7: To better fit within thecell, long pieces of double-stranded DNA are tightly packedinto structures calledchromosomes.

Figure 8: In

eukaryoticchromatin, double-stranded DNA(gray) is wrappedaround histoneproteins (red).

Figure 9: Supercoiledeukaryotic DNA.

How is DNA packaged within cells?

A complete strand of human DNA has about 3 billion base pairs: uncoiled, itwould be about 2m long!


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How do we know DNA is the heritablematerial?

Goals: Understand the early experiments

that determined DNA carried heritableinformation.

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R strain S strain

Photographs of Pneumococcus Strains

R SWhat is the Heritable Material?



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Griffiths Experiments on Bacterial Transformation

Hypothesis: Material in dead cell can transform living cells.

What is the Heritable Material?


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But, what is the heritable material?

Candidates: Amino Acids (protein)

or dNTPs (DNA)

What is the Heritable Material?


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Avery MacLeod McCarty Transformation Experiments (1944)

Treated virulent, heat-killed S strainwith various digestive enzymes

(-ase suffix indicates its an enzyme,the first part of the name tells yousomething about its function)

Added treated S-strainto living R-strain (non-virulent) and injectedinto mice


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Hershey & Chase Experiment

3 viruses

Biol200 - Concepts in Biology 23What is the Heritable Material?


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infection

5 minutes


Remove phage

PhageHereditaryMaterial

PhageHereditaryMaterial



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DNA

protein




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protein




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DNA

protein




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Refined Phage Experiment

Table 1.2. Location of phage protein and DNA after infection of E. coli.



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DNA replication occurs in three major steps:

1) the opening of the double helix and separation of the DNA strands,

2) the priming of the template strand, and3) the assembly of the new DNA segment.

How do cells copy (replicate) DNA?


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- Initiator protein (not shown) unwinds short stretch of double-stranded DNA- A protein helicase (yellow) breaks apart the hydrogen bonds between the bases,

separating the strands- Enzyme primase (red) briefly attaches to each strand and assembles a foundation

(primer ) at which replication can begin


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Beginning at the primer sequence, DNA polymerase (blue) attachesto the original DNA strand and begins assembling a new,complementary strand.

It uses free-floating nucleotides to build the new strand, matchingeach nucleotide in the template strand with its complementarynucleotide, creating an anti-sequence.

lecture 5 - dna

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