DNA, Chromosomes, and Sex Determination

Human cells are eukaryotic or prokaryotic cells?

Eukaryotic - they have a nucleus

In the nucleus, what do our cells contain that is like “a book that contains instructions”?

Chromosomes - we have 23 pairs

What are chromosomes made of?

Genes: One chapter of the book

DNA: Individual words or letters

The chromosomes contain genes, but are physically made up of the DNA molecule wrapped around proteins (histones)

What is the primary structure of DNA and RNA?

A chain of many nucleotide units linked together (polymer)

What is a nucleotide?

Repeating units of DNA and RNA made up of:

• Pentose sugar

• Phosphate Group

• Nitrogenous Base

What is the major difference between ribose and deoxyribose?

Deoxyribose does not contain a second OH group, rather it is just an H

Is DNA or RNA less stable?

RNA is less stable than DNA because of the OH group

Phosphate group traits

• They carry a negative charge essential for functions of DNA

• It is always bonded to the 5’ carbon atom of the sugar

What are the four nucleotides?

dAMP, dGMP, dTMP, dCMP

Purines

• Pure As Gold

  • Adenine

  • Guanine

Pyrimidines

• CUT

  • Cytosine

  • Thymine (DNA)

  • Uracil (RNA)

One purine pairs with one pyrimidine to maintain the same width of dsDNA. What are the pairs?

• A+T

• G+C

Why can’t we bond A and C?

There is a third bond on C that A cannot bind to

Polynucleotide strands of DNA run _____________

antiparallel

Phosphodiester bonds

Bonds between 5’ PO₄ and 3’ OH groups of adjoining nucleotides

Hydrogen bonds are between:

complementary bases of opposite strands - intermolecular

What base pairs have two H-bonds and what base pairs have 3 H-bonds?

A-T = 2

G-C = 3

Complementary base pairing is crucial for every part of DNA. Many procedures like ________ are based on complementary base pairing.

Hybridization

Denaturation and renaturation

dsDNA → ssDNA → dsDNA

Melting temperature

Temperature at which DNA becomes denatured

Why is it more energy required to denature GC base pairs than AT base pairs?

Since there are more H-bonds in GC base pairs, a higher temperature is required to denature the protein.

Abbreviations

ssDNA: single stranded

dsDNA: double stranded

bp: base pair

Kb: kilo base pair

Mb: mega base pair

Secondary structures in ssDNA and RNA?

Hairpins (loops) and stems

• Intramolecular H-bonds: bonds in the same molecule

The secondary structure of DNA is

the DNA double helix - 2 strands are antiparallel and held together by H-bonds between complementary bases

Prokaryotic cell traits

• No nucleus

• Small

• One circular DNA molecule

• Not complexed with histones

• Small amount of DNA

• No membrane bounded organelles

Eukaryotic cell traits

• Nucleus

• Relatively large cell

• Multiple linear DNA molecules

• Complexed with histones

• Relatively large amount of DNA

• Membrane bounded organelles

Tertiary structure of bacterial DNA

Supercoiling - condensing the DNA

Topoisomerases: add or remove rotations in DNA by breaking and then rejoining DNA strands

Tertiary structure of eukaryotic DNA

Linear chromosomes - dsDNA and a diverse array of proteins

Organized as a chromatin: DNA and associated proteins of a chromosome