BIO 212 unit 2- genetic code and gene expression, transcription and translation

gene expression

the process of translating information in DNA (genotype) into functioning molecules within a cell (phenotypes)

Beadle and Tatum

proposed that the function of a gene could be determined by knocking it out with a mutation “one ought to be able to discover what ones do by making them defective”

beadle and Tatum results

-bread mold was irradiated to create mutants

-one mutant lacked an enzyme to make pyridoxine (vitamin B6)

-mutation was in only ONE GENE

^lead to: “one gene, one enzyme” hypothesis

most geneses contain the instructions for making

polypeptides and proteins

Central Duma of Molecular Biology

the sequence of bases in DNA is a code

-DNA is ONLY an information storage molecule

-must be read by some intermediate molecule and translated into proteins

DNA is in the ______, and proteins are manufactured in the _______

nucleus, cytoplasm

Jacob and Monods hypotheses

RNA molecules are the intermediary between DNA and proteins (mRNA carries info to site of protein synthesis)

central dogma of molecular biology sequence

DNA nucleotides (info storage) → transcription → RNA nucleotides (info carrier) → translation → proteins (info machinery)

DNA is ______ to mRNA

transcribed (the process by which hereditary info in DNA is copied to RNA)

mRNA is _______ to protein

translated (the process by which time order of nucleotides bases in RNA is concerted to the order of amino acids)

genotype determined by sequence of bases in _____, which phenotype is a product of the _____ it produces

DNA, proteins

Gamow predicted that each word in the genetic code contains

three bases (triplet code/codon)

start codon, signifies the the start of the protein-encoding sequence in mRNA

AUG (codes fo methionine)

there are 60 codons that code for

the other 19 amino acids (NOT the start one)

the 3 stop codons

UGA, UAA, UAG (not specific to an amino acid)

mRNA is read _____ to make correct amino acid

5’ to 3’

properties of genetic code

redundant (more than one cocoon), conservative (first 2 bases identical), unambiguous (one codon always codes for one amino acid), nearly universal (all codon specify the same amino acids in all organisms), non-overlapping (ribosome locks onto first codon, it reads each separate codon one after the other)

mutation

any permanent change to a genotype (may/not affect phenotype)

point mutation

permanent single base change (DNA polymerase inserts wrong base pair into newly synthesized strand of DNA)

chromosome level mutation

addition/deletion of chromosomes from karyotype

benefit mutation effect

increases fitness of organism

deleterious mutation effect

decreases fitness of organism

silent point mutation

change in nucleotide sequence that does not change the amino acid specified by a codon

missense point mutation

change in nucleotide sequence that changes the amino acid specified by a codon

nonsense point mutation

change in nucleotide sequence that results in an early stop codon

frameshift point mutation

addition/deletion of a nucleotide

RNA polymerase only synthesizes

one RNA strand from DNA

initiation phase of transcription

sigma protein binds to RNA polymerase → sigma binds to promoter sequences on DNA template strand → RNA polymerase opens the DNA double helix → Template strand threaded through RNA
polymerase active site → rNTPs start forming
complementary base pairs with template strand → sigma dissociates from RNA polymerase once initiation phase of transcription is complete

elongation phase of transcription

rNTPs continue to be added to the mRNA strand at the
active site → mRNA strand and template strand are separated at the zipper

termination phase of transcription

RNA polymerase transcribes a
transcription termination signal into
mRNA strand → mRNA forms hairpin
structure → separates RNA polymerase and mRNA
strand

RNA processing (protecting mRNA)

processing the primary transcript (pre-mRNA), enzymes cleave the 3’ end downstream of the poly (A) signal and add a poly (A) tail

bacteria takes the whole mRNA while eukaryotes have to

splice (segment) the mRNA

in eukaryotes the primary transcript (pre-mRNA) must be

processed

protein coding regions of eukaryotic genes (exons) are interrupted by

non coding regions

RNA splicing

spliceosome allows introns coded into mRNA are removed to form the rest of the exons together to form mature mRNA

alternative splicing of primary transcript allows for

more than one type of protein to be produced by a single gene

tRNA

secondary structure folds over into L-shaped tertiary structure, the 3’ end has CCA sequence that forms a COVALENT bond with the amino acid, triplet on loop is the anticodon that base pairs with mRNA codon.

ribosomal 2 subunits

smalls subunit holds mRNA in place during translation, large subunit has site where peptide bonds form (active site)

translation has ____ sites

3

TRANSLATION: A-site

first site - acceptor site for an aminoacyl tRNA, forms peptide bonds

TRANSLATION: P site

middle site - tRNA attached to trowing polypeptide chain where peptide bonds form an active site above A and P sites

TRANSLATION: E site

last site - where tRNAs no longer bound to an amino acid, exit the ribosome

translation occurs in the

ribosome

initiation phase of translation

mRNA binds to small subunit and liens AUG start codon, initiator aminoacyl tRNA binds to start codon, large subunit binds to complete complex

termination phase of translation

occurs when the A site encounters a stop codon