Biomedical Science - Unit 1 DNA

James Watson and Francis Crick

Discovered that DNA was double helix

Nucleotide

Building block of DNA

Nucleotide Bases

Fundamental building blocks of DNA and RNA. They include adenine, guanine, cytosine, and thymine. A pairs with T and C pairs with G, and hydrogen bonds form in between them.

Sugar Phosphate Backbones

Structural framework of DNA and RNA molecules. Forms sides of DNA doble helix

Purine-purine

Not enough space in double helix

Pyrimidine-pyrimidine

Too much space in double helix

Purine-pyrimdine

Just right space in double helix

Antiparallel

In a double stranded DNA, backbones must run in this direction

X-Ray Crystallography

Determines position of atom in molecule

Schematic Diagrams of DNA Structure

Space-filling Model of DNA Double Helix

Non-covalent Interactions

Interactions between any 2 molecules or between different groups of the same molecule that don’t involve covalent sharing of electrons. Allows molecules to attract to each other. Examples: hydrogen bonds (permanent dipole), ionic, and hydrophobic effect

Induced Dipole

Non-polar bonds; bunch of electrons orbiting around. Creates a weak dipole (ripple effect). Temporary shift of electrons in a molecule or atom that creates a temporary dipole, only lasts a fraction of a second because they even out. Occurs in O2, N2, CH4. Examples: interactions between noble gases (e.g., He–He) or non-polar hydrocarbons.

Permanent Dipole

Polar bonds; one positive, one negative pole. Unequal sharing of electrons in a covalent bond due to differences in electronegativity. Occurs in HCl, H₂O, NH₃. One atom pulls electrons more strongly than the other, making one side partially negative (δ⁻) and the other partially positive (δ⁺). Examples: Water molecules attract each other through dipole-dipole interactions.

Ionic Bonds

Permanent dipole can induce a dipole in another molecule. Complete transfer of electrons from a metal to a non-metal, forming oppositely charged ions. Occurs in NaCl, MgO, CaF₂. Strongest type of bond. Example: Sodium chloride (Na⁺Cl⁻), held together by strong electrostatic attraction.

How Mutations Occur

When sequence of the DNA basis is changed

Polymorphic Traits

Trait that appears commonly in two or more different forms

George Mendel

Worked on how genes are passed down through one generation to the next through his pea experiment. (Genetic determinant for wrinkled genes = recessive, for round seeds = dominant). Found 3:1 dominant to recessive

Parental Cross (P)

First cross

Fillial (Fl)

Offspring

Genes

Segments of four types of nucleotides in a segment of DNA

Traits

Controlled by genes

Two

How many alleles does each individual carry for each gene

Genotype

Combination of alleles found in an individual

Principle of Independent Assortment

Alleles of different genes are transmitted independently of each other

Pedigrees

Used to examine inheritance of normal traits (or disease traits) in families

Segregation

Separation of two alleles (50 50 chance you’ll get either of them)

DNA

Molecule that stores instructions for building proteins

Transcription

The process by which a gene’s DNA sequence is copied into messenger RNA (mRNA).

Translation

The process by which the mRNA sequence is used to build a protein (a chain of amino acids) in the ribosmoe