DNA (genetics)

DNA

• “Deoxyribonucleic Acid”

• CHARAC: Polymer/Polynucleotide (composed of multiple repeating monomers)

• FUNC: Carries the genetic blueprint/instructions for building, running, and repairing an organism + expresses hereditary information

who determined the the structure of DNA? (2)

James Watson + Francis Crick

how did the discovery of DNA’s structure support three of its key properties?

Double Helix Model shows:

• Information storage (letters for nitrogenous bases spell out instructions)

• Replication (complementary base pairs mean each strand can act as a template to create another replica of DNA)

• Mutation (changes/errors can cause genetic variation/evolution)

Why did protiens seem better suited for storing genetic info?

• It was seen as more versatile/physically complex (with 20 different amino acids = endless combinations/shapes to fold into)

• DNA was thought to be too simple (only 4 diff amino acids)

DNA in cells (Loc, structure x2)

Eukaryotic Cells: (animals, plants)

• LOC: Nucleus, organells

• STRUC: divided into chromosomes + wrap around Histones

Prokaryotic Cells: (bacteria)

• LOC: free-floating in nucleoid

nitrogenous bases + Chargaff’s Rule/complementary base pairing + ring type + # and type of bonds

Adenine, Thymine, Guanine, Cytosine

• rings contain Nitrogen (N)

• A+T: 2 Hydrogen Bonds

• G+C: 3 Hydrogen bonds

nucleobases

Purines (adenine, guamine) and Pyrimidines (cytosine, thymine)

• “Pure As Gold”

• “Pie is CuT”

DNA Nucleotide

• The monomer (basic building block) of DNA

• Includes: Pentose sugar (deoxyribose), Phosphate group, Nitrogenous base

DNA Nucleoside

• A portion of the nucleotide without the phosphate group

• Includes: Pentose sugar (deoxyribose), Nitrogenous base

DNA structure (flat)

DNA structure 3D

• Has 6 billion bases, 3 million pairs

DNA shape

DOUBLE HELIX: Two strands of polynucleotides spiraling around an imaginary axis (translated into a helical shape)

Antiparallel

The backbones (in the DNA double helix) running in opposite directions (5’ —> 3’) from each other

• based on where the phosphodiester bonds form on the carbons of deoxyribose sugar (‘5 phosphate OR ‘3 hydroxyl)

• necessary for the double helix shape/twist

Labeling #’ on a deoxyribose sugar + determining 5’ vs 3’ ends

• 1’ ALWAYS starts clockwise from the 5’ (which is ALWAYS attached to the phosphate group) —> then go clockwise from there

• 3’ end = 3’ is sticking up, nucleotide looks upside down

• 5’ end = 5’ is sticking up, nucleotide looks right side up

DNA Grooves

Major Groove: wider gap between the backbones (backbones farther apart)

Minor Groove: smaller gap between the backbones (backbones closer together)

less than 30 nucleotide

oligonucleotide

more than 30 nucleotide

polynucleotide

# of rings for Deoxyribose, Adenine, Guanine, Cytosine, and Thymine

Deoxyribose: 1

Adenine (Purine): 2

Guamine (Purine): 2

Cytosine (Pyrimidines): 1

Thymine (Pyrimidines): 1

Hydrogen Bonds

• connect nitrogenous bases

• maintains the double helix shape + allows unwinding of both strands

Purpose of unwinding DNA

• whenever the cell needs to read/copy the genetic code (stored by DNA)

• DURING: DNA replication, Transcription (Protien synthesis)

Phosphodiester Bond

A strong chemical bond between two nucleotides, forming the backbone of DNA

atom(s) common to all three parts of a nucleotide

carbon (C), hydrogen (H)

atom found in a base but not found in a phosphate or sugar

nitrogen atom

atom found in a phosphate but not found in a base or sugar

phosphorus atom

which parts of two nucleotides interact when forming a DNA strand

phosphate group and pentose sugar (deoxyribose)

Which part of a nucleotide is not involved in forming the sugar-phosphate backbone of DNA

nitrogenous bases

what part of the nucleotide forms the inside of the double helix (“rungs of the ladder”)

nitrogenous base

why is DNA called a double helix?

because two polynucleotide strands are formed and then twisted around each other by the hydrogen bonds (from the nitrogenous bases of each strand) + they are twisting around an imaginary axis

Prime (‘)

• used to indentify the carbon atoms in the deoxyribose sugar

• EX: 2’ carbon, 5’ carbon

what groups stick out of the 5’ and 3’ ends of DNA?

5’= phosphate group

3’= hydroxyl group

which two nitrogenous bases appear to have more atoms (bec of rings)

Guanine and Adenine

Mitosis

• to split genetic material EVENLY/ACCURATLEY into two new cells

• DNA tightly coils up to the point when you can see the chromosome (X shape) — prevents tangling/tearing

Diploid # of chromosomes (human somatic cell VS. gamete)

*shown through karyotypes*

Human somatic cell:

• 46 (23 pairs)

• two complete sets (one for each parent)

Gamete:

• 23 (no pairs)

• single sets

Karyotype

• An organized visual profile of one’s complete set of chromosomes

• Arranged by size (big —> small), banding pattern, and shape

Why were strawberries used for DNA extraction?

• They are Octoploids (have 8 sets of chromosomes), which allows one to see the DNA more easily

• Cheaper, safer (allergens), smushable

Function of each step in strawberry DNA extraction

Mashing fruit = physically breaks open cell walls/membrane and releases DNA

Dish soap = dissolves/breaks open lipid bilayers of the cell membrane

Salt = neutralizes negative charges on DNA’s sugar phosphate backbone, allowing strands to clump up

Ice-cold isoporpyl alcohol = makes DNA strands clump up and percipitate out of the solution, isolating it (DNA cannot dissolve in alcohol)