Download The Blueprint of Life, From DNA to Protein

From DNA to Protein
Chapter 8
Terminology
• Genetics
• Genome
• Chromosome
• Gene
• Locus
• Alleles
• Genotype/Phenotype
• Heredity
• Living cells must accomplish two general
tasks to multiply and survive
– DNA replication
– Gene expression
• Expression involves two process
– Transcription
– Translation
– Flow of information from DNA to RNA to protein
DNA
• Polymer of nucleotides
• Hydrogen bonds between
complementary bases
– AT and CG
• Antiparallel
• New nucleotides can only be
added to the “free” 3’ end
DNA synthesis involves
anabolic polymerization
Monomers (Triphosphate
deoxyribonucleotides)
provide required energy for
DNA synthesis
Replication produces two DNA
double helixes
Each contains one original
strand and one new strand
One DNA
double helix.
Semi-conservative DNA replication
Two identical DNA
double helixes, each
with one parental
strand (blue) and one
new strand (pink).
• DNA replication in bacteria is bi-directional
– due to closed circular chromosome
– replication forks eventually meet and two
complete loops are separated
• Bacterial DNA is attached at several points
to the cell membrane
– Enzymes need for replication are membrane
proteins
• Topoisomerase (DNA gyrase)
• Helicase
• Primase
• DNA polymerases
• DNA Ligase
• Bacteria replication involves methylation of
daughter stands
– Methylase
– Adds methyl group (-CH3) to nitrogenous bases
(typically adenine)
• Methylation functions:
– Initiation of DNA repliction
– Control of genetic expression
– Protection from viral infection
– Repair of DNA
DNA Replication
• As DNA unwinds, it
creates a replication
fork
• As nucleotides are
added, the replication
fork moves down the
parental strand
– Leading strand
• Is synthesized CONTINUOUSLY as the DNA
polymerase moves towards the replication fork
– Lagging strand
• Is synthesized DISCONTINUOUSLY in pieces
as DNA polymerase moves away from the
replication fork
• Okazaki fragments
Single Strand Binding Proteins
• DNA contains the instructions for protein
synthesis
– Genes
• RNA carries out the instructions
• Genetic information flows from DNA to RNA
to protein
• Central Dogma of Molecular Biology
– DNA
– RNA
Transcribed
Translated
RNA
Protein
Gene Expression
• Transcription
– RNA polymerase synthesizes complementary mRNA from
DNA template
– Cytoplasm of prokaryotes and the nucleus of eukaryotes
Concurrent RNA transcription
Multiple copies of RNA can be transcribed simultaneously
• Eukaryotic DNA is more
complex
– Requires posttranscriptional
modifications
– Spliceosome
– Cap and tail
• Translation
– The language of mRNA is in the form of codons
• Three nucleotides situated next to each other on DNA
– Sequence of codons determines sequence of
amino acids in the protein
– 64 codons make up the “alphabet”
• 61 are sense codons
• 3 “stop codons”
•The site of translation is the ribosome
• tRNA brings appropriate amino acid to site of translation
• Each tRNA has an anticodon
– complementary sequence to the mRNA codon
In a prokaryotes, many
molecules of mRNA can
by transcribed
simultaneously
Why can translation begin
before transcription is
completed in a prokaryote
but not in a eukaryote?
gene
DNA
complementary
DNA strand
template DNA
strand
codons
mRNA
anticodons
tRNA
amino acids
protein
methionine
glycine
valine