Bio Unit 7 - Protein Synthesis and Biotech

Central Dogma

DNA makes RNA makes Proteins

Gregor Mendel

Father of genetics, discovered “heritable factors” passed from parents to offspring

Thomas Hunt Morgan

Proved genes are carried on chromosomes, which helped identify genetic material as either proteins or DNA

Frederick Griffith

Found that when pathogenic bacteria were heat-killed and then mixed with living non-pathogenic bacteria, the living cells became pathogenic — transformation, assimilation of foreign DNA by a cell.

Edwin Chargaff

Chargaff’s rule — amount of adenine always equals the amount of thymine, same for cytosine and guanine. Percentage of bases varies between species.

Avery-McCarty-Macleod

Isolated solutions containing heat-killed bacteria cells and examined whether transformation still occurred — only occurred when DNA was present.

Hershey and Chase

Showed DNA was genetic material of a bacteriophage through centrifuging cells: when radioactivity was in phage protein then placed in bacteria, the radioactivity was in the liquid (meaning it was not found in the bacteria); when radioactivity was in phage DNA, radioactivity was in the pellet (found in bacteria)

Rosalind Franklin

Used X-ray crystallography to examine DNA fibers; concluded it was a helix

Watson and Crick

Used Franklin’s image (w/out her permission) and Chargaff’s discovery to determine final structure of DNA

DNA Structure - Watson and Crick

Two nucleotide strands that run antiparallel; each strand has a 5’ and 3’ end; strands held together with hydrogen bonds; double helix

Nucleotide Structure

5-carbon sugar, deoxyribose or ribose; nitrogenous base attached to 1’ carbon, 2’ carbon determines DNA vs RNA; 3’ carbon is where other end of phosphate group attaches to; 5’ carbon is where phosphate group attaches to

Nitrogenous bases

Purines have one ring — Cytosine, Uracil/Thymine. Pyrimidines have two — Adenine and Guanine. Adenine and thymine/uracil are joined by two hydrogen bonds, cytosine and guanine are joined by three

Semi-Conservative Replication

Each broken strand serves as a template for a new strand.

Origins of Replication

Location where DNA strands are separated, creating replication bubble. Eukaryotes have many, prokaryotes have one. Each end of bubble has a replication fork that moves in each direction from the origin until it meets another bubble.

DNA Replication

Occurs in nucleus, interphase (synthesis)

Helicase

Unwinds DNA at replication forks by breaking hydrogen bonds between nitrogenous bases

Topoisomerase

Relieves strain that helicase creates; unwinding creates tighter twisting ahead of the fork.

Primase

Places RNA primer which tells DNA Polymerase where to begin replication

DNA Polymerase III

Adds nucleotides complementary to template strand; reads 3’ → 5’, builds 5’ → 3’

Leading and Lagging Strands

Directionality of DNA synthesis causes template strands to be copied in opposite directions. Lagging strand has Okazaki fragments that must be primed separately (actual complementary strand is built 3’ → 5’ in fragments).

DNA Polymerase I

Replaces RNA primers with DNA

Ligase

Glues fragments of DNA together (Okazaki fragments, replication bubble meeting points)

Proofreading

DNA Polymerase; If bases are paired incorrectly, nucleotide removed

Mismatch Repair

After replication, other proteins scan for mismatched bases and replace them

RNA Structure

Single stranded made of nucleotides containing pentose; uracil, adenine, guanine, cytosine

mRNA (Messenger RNA)

Copies the genetic code from DNA and brings information to ribosomes; has codons that code for a specific amino acid; 3 nucleotides = codon.

rRNA (ribosomal RNA)

Bind with proteins to create ribosomes; small and large subunit; site of protein synthesis.

tRNA (transfer RNA)

Bring amino acids to ribosomes so a polypeptide chain can be built; contains an anticodon

Transcription

Inside nucleus; G1 and G2; Initiation, elongation, termination

Initiation

Requires a promoter: control sequence of DNA telling RNA polymerase where to start transcription. Transcription factors bind to a promoter and recruit RNA polymerase to initiate transcription.

Elongation

RNA polymerase unwinds DNA, adds nucleotides to 3’ end, and proofreads

Termination

Specified by specific DNA sequence to separate new RNA from DNA

mRNA Processing (EUKARYOTES ONLY)

pre-mRNA must be modified before leaving nucleus; 5’ end receives GTP cap, 3’ end gets poly-A tail; protect mRNA, help ribosomes attach to 5’

Exons and Introns

Introns are long noncoding stretches of nucleotides, exons are coding regions that will be translated to an amino acid sequence. Spliceosome removes introns, joins exons, creating mature mRNA molecule. Prokaryotes do not have introns.