DNA and Genes
The Molecular Basis of Inheritance
Gene Expression: From Gene to Protein
in 1952, Alfred Hershey and Martha Chase showed that DNA is the genetic material of phage T2 in an experiment they designed
step 1: phages infect cells
conclusion: the injected DNA from the phage provides genetic information
step 2: agitation frees outside phage parts from cells
step 3: centrifuged cells form a pellet
step 4: measured the radioactivity in the pellet and the liquid
Rosalind Franklin took an X-ray diffraction photo of DNA
detailed steps of translation:
types of mutations
detailed steps of transcription
elongation: promoter s at start point and contains unwound DNA and RNA transcript
termination: promoter moves farther down strand and there's a longer RNA transcript and rewound DNA
initiation: promoter is at start point and contains RNA polymerase
small ribosomal subunit binds to mRNA
large ribosomal subunit complexes the initiation complex
codon recognition
peptide bond formation
substitutions: nucleotide-pair substitution replaces one nucleotide and its partner with another pair of nucleotides
insertions and deletions: additions or losses of nucleotide pairs in a gene
point mutations: changes in just one nucleotide pair of a gene
frameshift mutation: altered reading frame
detailed DNA structure
DNA replication in prokaryotes and eukaryotes
steps of DNA replication
figures
telomeres
two strands > double helix
one strand has a 3' end and a 5' end and the other strand has the same but on opposite sides
nitrogenous bases
sugar phosphate backbone: made up of phosphate groups, DNA nucleotide, and sugar
thymine (T)
guanine (G)
cytosine (C)
adenine A)
prokaryotes replicate in bubbles and eukaryotes replicate in strands
both have a double-stranded DNA molecule, parental strand, daughter strand, and replication fork during the process
a eukaryotic chromosome may have hundreds or even thousands of origins of replication, while prokaryotes just have one per cell
they both result in just two daughter DNA molecules
each base pair is paired by hydrogen bonding with its specific partner, A with T and G with C
the two DNA strands are separated and can now serve as a template for a new complementary strand
nucleotides complementary to the parental strand are connected to form the sugar-phosphate backbones of the new daughter strands
figure 16.14 addition of a nucleotide to a DNA strand: DNA polymerase catalyzes the addition of a nucleotide to the 3' end of a growing DNA strand, with the release of two phosphates
figure 16.15 synthesis of the leading strand during DNA replication: after RNA primer is made, DNA pol III starts to synthesize the leading strand. the leading strand is elongated continuously in the 5' > 3' direction as the fork progresses
figure 16.16 synthesis of a lagging strand: steps of the synthesis of the lagging strand at one fork
figure 16.17 a summary of bacteria DNA replication: left-hand replication fork of the replication bubble; half of the daughter strand is the leading strand and the other half is the lagging strand
special nucleotide sequences at the end of eukaryotic chromosomal DNA molecules
they do not prevent the shortening of DNA molecules, but they postpone the erosion of genes near the ends of DNA molecules
the shortening of telomeres is connected to aging
telomerase, an enzyme, catalyzes the lengthening of telomeres in germ cells
translocation
tRNA structure
amino acid attachment site
hydrogen bonds
anticodon
four base pair regions and three loops
polyribosomes
can be seen with an electron microscope
they enable a cell to rapidly make copies of a polypeptide
when a ribosome is far enough past the start codon, a second ribosome attaches to the mRNA, resulting in a number of ribosomes trailing along the mRNA
can be either free or bound