GN 301 Module 3: DNA, RNA, and Chromatin Structure

DNA and Research

DNA stands for deoxyribonucleic acid

  • Friedrich Miescher

Identified DNA from white blood cells and called it nuclein, noting it was slightly acidic

  • Boveri and Sutton

Found chromosomes and proposed the chromosome theory of inheritance

What was thought to be the genetic material prior to determining that it was DNA?

  • ==Protein== was thought to make up the genetic material because it makes up about 50% of the cell. People thought that because proteins have a lot of variability and are used for many functions.

Important Researchers

  • Avery, McCarty and MacLeod

Showed that DNA can transform the properties of cells by studying how DNA transformed bacteria

  • Albrecht Kossel

Discovered that DNA was composed of 5 nitrogen bases: adenine, thymine, guanine, cytosine, and uracil

  • Phoebus Levene

Discovered and named the nucleotide (sugar + base + phosphatase)

  • Maurice Wilkins and Rosalind Franklin

Came up with x-ray experiment to take pictures of DNA structures, discovering that it was helical

  • Erwin Chargaff

Researched the percentages of bases present in different animals and compared the ratios

  • James Watson and Francis Crick

Put together the first DNA replica structure from Wilkins and Franklin’s research

DNA Components

==DNA Components: 1 nucleotide = 1 sugar + 1 base + 1 phosphate==

Difference between ribose (in RNA) and deoxyribose (in DNA)

  • Ribose has a hydroxyl group at position 2
  • Deoxyribose has a hydrogen atom at position 2

Bases: Purines vs. Pyrimidines (contrast structure, list names of each)

  • ==Purines==

    • Adenine and guanine. They have a two-ringed structure consisting of a 9-membered molecule with 4 nitrogen atoms.

  • ==Pyrimidines==

    • Cytosine, thymine, uracil. They have a single-ringed structure with 5-members and 2 nitrogen atoms.

  • Base difference between DNA and RNA:

Thymine in DNA, uracil in RNA

  • Nucleotide Construction:

Base is connected to 3’ carbon of sugar. Phosphate is connected to 5’ carbon of sugar.

  • Describe complementary base pairing: between which bases and how many hydrogen bonds joining each pair?

==Adenine and thymine== pair up, while ==guanine and cytosine== pair. 2 hydrogen bonds pair adenine and thymine, while 3 bonds pair guanine and cytosine.

  • Describe the properties of the Watson Crick Model of DNA

Bases along length of 1 strand joined by hydrogen bonds

  • DNA has a negative charge (positive or negative) – why?

Because of the phosphate groups (PO_4-)

DNA Structure

  • Complementary strands

DNA copy of a mRNA molecule produced by reverse transcriptase

  • Antiparallel

Parallel but moving in opposite directions

How many base pairs per turn?

  • 10 1/2

Diameter of helix?

  • 1.8 nm

Length of 1 turn?

  • 3.4 nm

Distance between base pairs?

  • 3.4 angstroms

Plectonic coil:

  • A type of coiling of a double‐stranded helix in which the two strands are intertwined; they may not be separated without uncoiling.

Right handed coil

  • the banister handle is on the right side

Hydrophobic

  • bases in the center;

Hydrophilic

  • backbone on the outside

What forces hold the 2 strands of DNA together?

  • Hydrogen bonds

List differences between DNA and RNA structure:

  • RNA contains the sugar ribose, while DNA has deoxyribose.
  • DNA is double-stranded, RNA is single-stranded
  • Thymine in DNA, uracil in RNA

Chromatin

Define chromatin and histone and relate these to chromosome structure.

  • Chromatin- complex of DNA (proteins and RNA)
  • Histone- protein found in chromatin \n

Chromatin is found in DNA in the nucleus, where it forms chromosomes in the nucleus. Histones are found in the chromatin.