From Gene to Protein

The process by which DNA directs the synthesis of proteins (in some cases, just RNA)

 Transcription: the synthesis of RNA using information in the DNA  In nucleus  DNA  mRNA (made by RNA polymerase)  Translation: the synthesis of a polypeptide using the information in RNA  In cytoplasm on a ribosome  mRNA  polypeptide (protein)

RNA  Single stranded  Ribose sugar  Uracil  DNA monomers: nucleotides  Protein monomers: amino acids DNA  Double stranded  Deoxyribose sugar  Thymine

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 3 bases in a row made a “word”  These words are transcribed into complimentary words of mRNA (A-U and G-C)  Then these words are translated into amino acids forming polypeptides Practice:  How many codons are represented ACCACCAGTAAA  What would be the complimentary mRNA strand? UGGUGGUCAUUU

 More than one codon codes for same amino acid but no codon codes for more than one type of amino acid  Why do you think this could be helpful?

 The DNA code is nearly universal!

RNA Polymerase  Enzyme that uses the DNA template strand to transcribe a new mRNA strand  Does not need a primer

Transcription Unit  The stretch of DNA that is transcribed into an RNA molecule

Transcription Process is divided into 3 steps  Initiation  Elongation  Termination

Initiation 1. RNA polymerase binds to the promoter 2. DNA strand unwinds 3. RNA polymerase initiates RNA synthesis at the start point on the template strand.

Elongation 1. RNA polymerase moves downstream, unwinding the DNA, and elongating the RNA transcript 5’-3’ 2. The DNA strands re- form the double helix helix

Termination 1. RNA transcript is released 2. RNA polymerase detaches from the DNA.

Promoters!  RNA polymerase binds very precisely to the promoter (portion of DNA)  (determines where transcription starts and which DNA strand will be the template)  Transcription factors help RNA polymerase bind and initiate.  Transcription does not start without these!  Transcription factors +RNA polymerase II (bound to the promoter) = transcription initiation complex qk vg

TATA Box  Crucial promoter DNA sequence  25 units upstream from start point (a nucleotide sequence on non-template strand)

RNA Processing  Precursor mRNA (pre-mRNA) is made into mature mRNA that will be transported to the cytoplasm for translation!

RNA Processing  5’end receives a 5’cap placed on after the mRNA is synthesized  3’end receives more adenine nucleotides = poly-A tail ZYA

Functions of 5’ cap and Poly-A Tail  Facilitate the export of the mature RNA from the nucleus  Protect the mRNA from degradation by hydrolytic enzymes  Help ribosomes attach to the 5’end of the mRNA

RNA Splicing (Pre-mRNA to mRNA)  Introns: non-coding segments  Exons: coding segments ( exons are expressed)

snRNPs  Small nuclear ribonucleoproteins: recognize splice sites on ends of introns  snRNPs binds to ends of introns  Splicosomes do the cutting

Spliceosomes  Reacting with certain sites along the introns, releasing the intron which then disintegrates.  Nucleotides match up between spliceosomes and splice sites. w_pQ YNE

1. Initiation: ribosomes binds to mRNA at specific area 2. Elongation: ribosome starts matching tRNA anticodon sequences -Each time a new tRNA comes into the ribosome, the amino acid it was carrying gets added to the elongating polypeptide chain 3. Termination: a release factor reads the stop codon and synthesis ends

tRNA  Transfer RNA  Physical link between the mRNA and the amino acid sequence of proteins PSTQ UdY

Ribosome Structure  Large subunit + small subunit P A

Ribosome: A, P and E sites  A = holds the tRNA carrying the next amino acid “acceptor”  P = holds the tRNA carrying the growing polypeptide chain “polypeptide”  E = discharged tRNA’s leave the ribosome “exit” PA

Release Factor  Protein shaped like an aminoacyl tRNA. Binds directly to the stop codon in the A site.  Causes addition of a water molecule instead of an amino acid

 They coil and fold forming secondary and tertiary 3-D structure

 Eukaryotic: slightly larger and molecular composition slightly different than prokaryotic.  Certain antibiotics can inactivate bacterial ribosomes w/o harming the eukaryotic cell’s ribosomes

 Changes to the genetic information of a cell (or virus)

 change in a single nucleotide pair of a gene

 Insertion and deletion of a number of nucleotides not in multiples of 3.  Ex. Using words  The cat ate the rat hec ata eth era t

 1. spontaneous mutations  2. mutagens

 Nonsense: point mutation that changes an amino acid codon into a stop codon. Translation is terminiated prematurely.  Missense: one amino acid is changed to another amino acid

 Silent mutation: nucleotide change still codes for the same amino acid

 Mutagen: anything that causes DNA damage Types:  Physical (ex. Radiation)  Chemical (ex. Asbestos)

 Nucleotide analogs: pair incorrectly during DNA replication.  Some chemicals insert themselves into the DNA and distort the double helix  3. some chemicals cause changes in the bases

 Bacterial cells: stream-lined gene expression. Can transcribe and translate a gene at the same time.  Eukaryotic: segregate transcription from translation