Transcription and Translation of DNA How does DNA transmit information within the cell? PROTEINS! How do we get from DNA to protein??? The central dogma of Molecular Biology--- DNA  RNA  Protein What are proteins and RNA? (review)

What are proteins?  A bunch of amino acids joined together (peptides and polypeptides)  There are 20 Amino Acids: I.e. serine, threonine, leucine, valine, tryptophan…etc… Examples of amino acids: Threonine Tryptophan Valine

What is RNA?  Ribonucleic acid  Is single-stranded, but can fold back on itself  Ribose sugar (not deoxyribose like DNA)  Uracil is in place of thymine Uracil:

 RNA is used to get the message out of the nucleus and into the cytoplasm where proteins are made …So if there are 20 amino acids and only 4 nucleic acids how does this work? Need a code: 4 1 ? = ?= ?= 64! This combination of 3 nucleic acids is called a codon

Codons: (you don’t have to memorize these) Note that there is redundancy in the genetic code: 20 amino acids and 64 codons

1 st step: from DNA to RNA = TRANSCRIPTION  Objective is to make an accurate copy of a small section of an organisms DNA 4 Steps: 1.Initiation (Start signal located) 2.Elongation (copying of DNA to RNA) 3.Termination (Stop signal located) 4.Processing (Final changes made)

Initiation:  Each gene of double stranded DNA has a sense strand and an antisense strand. The sense strand contains the “instructions” for protein synthesis.  On the sense strand is a nucleotide sequence (called a promoter sequence) where RNA polymerase can bind. (RNA polymerase makes RNA)  The promoter sequence has two specific regions. One is rich in T and A nucleotides and is referred to as a TATA box. Blackboard

Elongation: (very similar to DNA replication)  RNA polymerase opens the DNA one section at a time  RNA polymerase works in the 5’  3’ direction, nucleotides added to 3’ OH group  Since RNA is single-stranded, no okazaki fragments  Many RNA copies of the same gene can be made MCB 0402

Termination:  RNA polymerase will continue along the DNA strand until a terminator sequence is encountered.  After this, the RNA polymerase molecule separates from the DNA strand AND the new RNA molecule dissociates as well.  the RNA is now called mRNA for messanger RNA

Processing:  this occurs only in eukaryotes  Initial mRNA molecule is called pre-mRNA 1.5’ end is “capped” with a modified G nucleotide. This is called a 5’ cap 2.3’ has a long string of A nucleotides added to it. This is called a poly-A tail These two things help protect the mRNA transcript

3. Splicing: eukaryotes have a bits of DNA that don’t code for anything (called introns) in between bits of DNA that do code for proteins (exons). Introns must be removed before the mRNA leaves the nucleus. This is done by a Spliceosome.