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Gene Expression From a gene to a protein Central Dogma • (Crick 1958) • Determines the genetic flow of information Central Dogma First step: a genetic message from DNA is to copied (transcribed) into mRNA, which contains the code for making proteins Second step: is to decode mRNA into a polypeptide chain which builds a protein. Functions of a Protein Functions of Protein: • Structural – muscle, hair • Chemical – antibodies, hormones, enzymes (regulate all chemical reactions in cells) Proteins • Proteins are made, from mRNA, by joining amino acids into long polypeptides (which are proteins) – There are only 20 naturally occurring amino acids Review of DNA • DNA is the genetic material • DNA codes for different genes – Genes are codes for a protein which determines different traits DNA is made up of nucleotides Which contain: - a phosphate group - a sugar (deoxyribose) - a nitrogenous base Structure of DNA RNA • Involved in protein synthesis • Made up of nucleotides: –Nitrogenous bases (RNA only has A, U, C, G there is no T!) –A phosphate group –A sugar (ribose) Types of RNA • There are three main types: –Messenger RNA (mRNA) –Transfer RNA (tRNA) –Ribosomal RNA (rRNA) mRNA • Messenger RNA (mRNA) carries copies of instructions for assembling amino acids into proteins. rRNA • Ribosomal RNA (rRNA). • Along with proteins make up ribosomes. tRNA • During protein construction, transfer RNA (tRNA) transfers each amino acid to the ribosome. Transcription • Flow of info: DNA -> mRNA • Location: Nucleus • mRNA is produced by copying part of the DNA – The mRNA leaves the nucleus and goes into the cytoplasm and attaches to the ribosome. Transcription • Messenger RNA is transcribed in the nucleus, and then enters the cytoplasm where it attaches to a ribosome. The Genetic Code • The genetic code is read from mRNA – mRNA made off of a strand of DNA is read. • mRNA is only 4 letters A, U, C, and G • The code is read 3 letters/bases at a time • Codon= three consecutive nucleotides which are specific for an amino acid Codons Translation • Flow of info: mRNA -> Proteins • Location: Cytoplasm/Ribosomes • Translation is decoding mRNA into a polypeptide chain(protein) Step 1 Translation • mRNA attaches to a ribosome • The start codon (AUG) is located by tRNA • The matching tRNA, containing the anitcodon UAC, will bind to AUG • The tRNA carries the animo acid specific to the mRNA sequence AUG, which is methionine. Step 2 •The ribosome binds new tRNA molecules and amino acids as it moves along the mRNA. Step 3 As each new tRNA enters the ribosome, one leaves. Before tRNA can leave the ribosome, the animo acids will bond together to make a polypeptide chain Step 4 The process continues until the ribosome reaches a stop codon. Mutations • Changes in genetic material • Many have little effect on gene expression or protein function • A few can be harmful and then some are good – Harmful mutations can cause cancer and genetic disorders – Good mutation can make altered proteins which may be beneficial in different/changing environments Point Mutations • Mutation of 1 or more nucleotides – Substitution – changing one base, usually only changes one amino acid – Insertion – addition of 1 or more bases, causes frameshifts – Deletion – removal of 1 or more bases, causes frameshifts Point Mutations Kinds of Mutations •Substitutions usually affect no more than a single amino acid. Chromosomal Mutations • Change in number or structure of a chromosome – Deletion – loss of all or part of a chromosome – Duplication – extra copies of parts of chromosomes – Inversion – reverse direction of parts of chromosomes – Translocation – chromosome breaks and attaches to another Chromosomal Mutations • Occur during Meiosis – Prophase I – Anaphase I or Anaphase II Nondisjuction • Error in meiosis in which chromosomes fail to separate. Changes to Chromosome Number • Monosomy 2n-1 – 45 chromosomes – Turners (XO) • Trisomy 2n+1 – 47 chromosomes – Down syndrome(trisomy 21), Klinefelters (XXY), Triple X (XXX), Jacobs (XYY) • Polyploidy (Triploid, Tetraploid, etc) Turners (45, XO) • 1 in 3,000 female births • Sterile females Down Syndrome •Mothers in early 20s 1 in 1,500 births •Mothers over 35 1 in 70 births •Mothers over 45 1 in 25 births Klinefelters (XXY) • 2 in 1000 male births • Sterile males Jacobs (XYY) • 1 in 1000 male births • Tall • Lower mental ability • Tendency for aggressivenes s