Cell Biology Chapter 3

molecular biology

mechanisms of transmission & expression of genetic info; model organisms provide info on mechanisms shared by all organisms (recombinant DNA techniques)

heredity

classical principles of genetics

Gregor Mendel studied?

inheritance patterns of traits and assumed that each trait is determined by a pair of inherited factors (genes)

allele

one gene copy

dominant

allele that determines phenotype

recessive

allele that will be masked by dominant allele

genotype

genetic makeup

phenotype

physical appearance

chromosomes

carriers of genes

diploid

2 copies of each chromosome; most plant & animal cells are this

meiosis

one chromosome from each pair transferred to progeny → haploid; how germ cells are formed

mutations

genetic alterations; affected physical characteristics in Drosophilia

gene segregation & linkage

tells if genes are different or same chromosomes

phenylketonuria

genetic defect in metabolism of Phe (deficiency in enzyme → genes specify synthesis of enzymes)

Neurospora crassa fungus

normal strains requires minimal media, mutant strains required specific amino acids (deficiency in a specific metabolic pathway → genes specify enzyme structure)

DNA as genetic material

encapsulated bacteria (S) → pneumonia, noncapsulated (R) → no pneumonia; cell-free extract from pathogenic S bacteria transforms R to S → pneumonia

-DNA is transforming principle

-viral DNA enters infected cell, not viral protein; DNA transferred to progeny

transforming principle

responsible for inducing genetic transformation of bacterial strain

structure of DNA

-hydrogen bonding in alpha helix of proteins

-double helix w/ sugar phosphate backbone, N bases inside

-anti parallel strands

-0.34 nm between bases, 3.4 nm per turn, 10 bases per turn

semiconservative DNA replication

DNA molecule separates → each strand becomes template for new strand; one strand of parental DNA conserved in each progeny DNA molecule

-Meselson and Stahl grew E. coli in ¹⁵N medium → “heavy” DNA; next gen in ¹⁴N → intermediate (hybrid DNA)

expression of genetic information

genes determine protein structure
-RNA is intermediate, nucleus → cytosol

-direct complementary base pairing b/w mRNA & protein is impossible

-amino acids attached to appropriate tRNA by tRNA synthetase (“charged RNA”)

-complementary base pairing occurs b/w tRNA & mRNA

central dogma

pathway for the flow of genetic info

-DNA —(transcription by RNA polymerase)→ RNA (mRNA template) —(translation in ribosome)—> Protein

-rRNA: component of ribosomes, tRNA: adaptor for amino acids

genetic code

nucleotide triplets encode amino acids

-mutations in bacteriophage DNA; if all 3 bases were mutated, WT phenotype was maintained

-normal gene → WT virus, +1 or +2 nucleotides → rll mutant, +3 nucleotides → WT virus

-stop codons not expressing genes, just ending translation

in vitro translation

in vitro systems that can synthesize proteins

-known mRNA sequence into test tube → in vitro translation → polypeptide

degenerate

many amino acids are specified by more than one codon