Protein synthesis

Beginning with dna DNA is found in the nucleus, but making a protein occurs at the ribosome (either floating in the cytoplasm or attached to the rough ER The DNA code must be copied and moved from the nucleus out to the cytoplasm Once in the cytoplasm, the code must be read so amino acids (building blocks of protein) can be assembled

DNA to RNA In order to get the DNA code out of the nucleus and into the cytoplasm, it must be turned into another nucleic acid called RNA

DNA to RNA RNA does not contain the base thymine – instead it has the base uracil A goes with U C goes with G The RNA molecule is single-stranded

types of RNA Messenger RNA (mRNA) – copies the DNA code and carries the information to the ribosomes outside the nucleus Transfer RNA (tRNA) – transfers amino acids to the ribosome, where proteins are made

Messenger RNA Long, straight chain of nucleotides Made in the nucleus - copies DNA and then exits out the nuclear pores Contains the nitrogen bases A, G, C, and U Carries information for a specific protein A sequence of 3 bases is called a codon AUG – start codon (amino acid is methionine) UAA, UAG, or UGA – stop codons

Transfer RNA Single-stranded molecule with an attachment site at one end for an amino acid The other end has three nucleotide bases called the anti-codon (complementary to the codon) amino acid attachment site U A C anticodon

The Genetic Code A codon designates a specific amino acid, however an amino acid may have more than one codon There are 20 amino acids and 64 possible codons One codon tells the ribosome to start translating (AUG), and three tell the ribosome to stop translating (UAA, UAG, or UGA )

The Genetic Code

The Genetic Code

Pathway to Protein

Protein Synthesis The production, or synthesis, of a polypeptide chain Polypeptide chain = protein A string of amino acids held together with peptide bonds There are two phases to making protein – transcription and translation

Transcription DNA  RNA

Transcription The process of copying the sequence of one strand of DNA (the template strand) mRNA copies the template strand

Transcription Practice: what would be the complementary RNA strand for the following DNA sequence? DNA 5’ – GCGTATG – 3’

RNA 3’ – CGCAUAC – 5’ Transcription Practice: what would be the complementary RNA strand for the following DNA sequence? DNA 5’ – GCGTATG – 3’ RNA 3’ – CGCAUAC – 5’

TransLATION RNA  PROTEIN

Translation The process of decoding the mRNA and turning it into a polypeptide chain (protein) Ribosomes read mRNA 3 bases (one codon) at a time

Translation End Product The end product of protein synthesis is a protein A sequence of amino acids bonded together with peptide bonds (also called a polypeptide) aa1 aa2 aa3 aa4 aa5 aa200 aa199

Overall Process Primary structure of a protein T A C G DNA A U G C mRNA start codon codon 2 codon 3 codon 4 codon 5 codon 6 codon 7 codon 1 methionine glycine serine isoleucine alanine stop codon protein Primary structure of a protein aa1 aa2 aa3 aa4 aa5 aa6 peptide bonds

Turning genes on and off Gene Expression Turning genes on and off

Gene Expression Gene = a specific sequence of nucleotides at a specific spot on a chromosome ALL body cells contain a complete copy of an organism’s genome (genome = all genes) What kind of cells do NOT contain a complete copy? However, not all genes are turned on in all cells Why? Each cell transcribes and translates certain genes from the DNA depending on the function of that cell

Mutations When genes change

Mutations Mutation means change There are several different types of mutations that can affect the DNA strand If the DNA strand is affected, the protein can also be affected?

Point Mutations Only a single nucleotide is changed (one point) This can also be called a substitution mutation Three things can result from a point mutation Silent mutation: no change in the amino acid Missence mutation: a change from one amino acid to another Nonsense mutation: one amino acid is changed to a STOP codon May have a smaller impact on the overall protein

Point Mutations

Frameshift Mutations Causes a change to the codon where the mutation is located AND to all the codons that come after it Two types of frameshift mutations Deletions – removal of a nucleotide Insertions – addition of a nucleotide Will likely have a larger impact since it likely changes the whole amino acid sequence (protein)

Frameshift Mutations

Impact of Mutations The impact of a mutation on an individual depends on where and when it occurs If there was a mutation in the DNA of a zygote, how would that impact the individual? How might a mutation in a skin cell affect an individual?

Mutation Examples