Unit 3 Bio: Day 1

Nucleotide

Monomer of nucleic acids

sugar + phosphate + nitrogenous base

Nucleic acids (DNA and RNA)

Polymers of nucleotides (polynucleotides); information molecules

Deoxyribose vs. ribose

Deoxyribose (DNA) has H on the 2' carbon; ribose (RNA) has OH

Purines

Adenine and guanine (two-ring bases)

Pyrimidines

Thymine, cytosine, uracil (one-ring bases)

Phosphodiester bond

Bond between adjacent nucleotides

Phosphodiester (sugar-phosphate) backbone

Repeating sugar and phosphate units joined by phosphodiester bonds

5'-to-3' orientation

A nucleotide chain has a 5' phosphate end and a 3' OH end; it is built and read in this direction

Double helix

Two polynucleotide strands connected by hydrogen bonds, wrapped around one axis

Antiparallel strands

The two DNA strands run in opposite directions (5' to 3' on one, 3' to 5' on the other)

Base-pairing rules in DNA

A with T (2 hydrogen bonds); C with G (3 hydrogen bonds)

Why must a purine pair with a pyrimidine?

Purine + pyrimidine gives the right width; purine + purine is too wide, pyrimidine + pyrimidine is too narrow

Chargaff's rules

In DNA, %A = %T and %G = %C (so purines = pyrimidines); G+C content varies by species

How RNA differs from DNA

Single-stranded, ribose sugar, uracil instead of thymine

What does DNA encode?

The information for the amino acid sequence of proteins

Other nucleotide-based energy molecules

ATP, NAD, FAD

Genome

All of a cell's DNA, packaged as double-stranded DNA molecules

Prokaryotic vs. eukaryotic chromosomes

Prokaryotes

Nucleus

Membrane-bound organelle in eukaryotic cells that contains the chromosomes

Genotype

What is in an organism's DNA

Phenotype

The result of the instructions from DNA (eye color, height, but also behavior or physiology)

Gene

A segment of DNA that encodes something affecting phenotype, very often a protein

Allele

A different version (variant) of a gene

Homologous chromosomes

Matched pairs (one maternal, one paternal) with the same length and same genes, but potentially different alleles

Locus / homozygous / heterozygous

Locus = location of a gene on a chromosome; homozygous = two identical alleles (AA or bb); heterozygous = two different alleles (Cc)

Somatic cells / diploid (2n)

All body cells except reproductive cells; 46 chromosomes (two sets of 23) in humans; diploid = two of each chromosome

Gametes / haploid (n)

Reproductive cells (sperm and eggs) with one set of 23 chromosomes in humans; haploid = one of each chromosome

Fertilization and zygote

Two haploid cells (egg and sperm) unite to make a new diploid cell, the zygote (2n = 46)

Chromatin

Complex of DNA and protein that tightly packs eukaryotic chromosomes

Nucleosome and histones

DNA coiled around 8 histone proteins about every 200 nucleotides; histones are positively charged and attracted to DNA's negative phosphate groups

Solenoid

Nucleosomes wrapped into higher-order coils, forming a 30 nm fiber about 50x shorter than extended DNA

Order of DNA compaction

DNA double helix, nucleosomes (beads on a string), solenoid/chromatin fiber, chromatin loops on protein scaffold, chromosome