12/29/102 Functional segments of DNA Code for specific proteins Determined by amino acid sequence One gene-one protein hypothesis (not always true)

12/29/103 Discovered by Franklin/Watson/Crick Composed of nucelotides – Pyrimidines- C/T – Purines- G/A – These always bond together (Chargaff’s Rule A-T C=G) Sugar and phosphate compose backbone Nitrogenous bases are variable and functional and compose genes

12/29/104 Covalent bond holds the phosphate to 5’C sugar on one end and 3’C sugar on the other DNA has a 5’(free P group) end and 3’ (free OH group) end N-bases attached to 1’C sugar and project into center, bonded by H bonds, AT (3 bonds), CG (2 bonds)

12/29/105 2 strands are complementary and antiparallel (run in opposite directions)

12/29/106 Replication is semi-conservative (1 old, 1 new strand) Helicase unwinds the DNA at many locations, replication fork starts in the middle of the strand and replication proceeds in both directions

12/29/107 DNA polymerase adds complementary bases to the exposed strand, these bases are free and floating in cell DNA polymerase can only add bases in the 5’ to 3’ direction Leading strand goes in one directing, lagging strand has Okaski fragments that are later joined by ligase.

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9 DNA polymerase is very accurate Many errors are corrected as DNA strand is being formed If error or physical damage occurs, nucleases excise (cut out) the damaged portions and other enzymes then fill in the gaps

12/29/1010 DNA- nucleotides ATCG, double- stranded, contains deoxyribose, large, more stable, contains genetic information RNA- nucleotides AUCG, single stranded, contains ribose, smaller, less stable, 3 types mRNA, tRNA, rRNA, directs protein formation

12/29/1011 Messenger RNA – Copies genetic info from DNA – Carries message to ribosomes – Serves as template during translation Transfer RNA – Reads info in mRNA – Transfers proper amino acid to the ribosome Ribosomal RNA – Most of mass of ribosome – Stabilizes RNA template – Allows translation to proceed properly

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13 Synthesis of RNA from DNA mRNA and tRNA transcribed in nucleus, rRNA in the nucleolus One strand of DNA is transcribed at a time

12/29/1014 RNA polymerase binds to specific DNA sequence in gene, called the promoter RNA polymerase causes DNA to unwind Another molecule of RNA polymerase brings in free RNA nucleotides and pairs with the exposed bases Uracil pairs with Adenine

Many molecules can be transcribed at the same time Stops transcribing at termination signal DNA rewinds The pre-mRNA is processed, introns (non coding segments are removed), a cap and poly A tail is added 12/29/10

16 Codon- 3 mRNA bases, code for 1 amino acid 64 possible codons, but only 20 amino acids, therefore code is redundant Same for all living organisms AUG- start codon- Met UAG, UAA, UGA- stop codons

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18 Synthesis of polypeptide from mRNA Occurs at ribosomes tRNA contains anticodon which is complementary to codons in mRNA

12/29/1019 Initiation- AUG becomes aligned in ribosome, initiator tRNA binds to ribosome and pairs with AUG, Met is bound Elongation- tRNA bonds with 2 nd codon, peptide bond forms between Met and 2 nd aa, Met detaches from tRNA and translation continues in 5’ to 3’ direction Termination- stop codon is reached, water molecule is added and polypeptide released from the ribosome, protein then folds into its proper shape

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21 Spontaneous mutations can occur, mutagens can cause mutations, most are harmful Beneficial mutations lead to natural selection 2 main types: point and insertions or deletions

12/29/1022 Point Mutations Change in 1 or few bases Substitution- replacement of 1 pair of nucleotides, may or may not be harmful Missense- codon specifies wrong amino acid, may or may not be harmful Nonsense- codon changed to stop codon, nearly all lead to cell death

12/29/1023 Insertions/Deletion Insertion- addition of 1 or more nucleotides Deletion- loss of 1 or more nucleotides Both are harmful Change the reading frame of mRNA message Frameshift- change all codons after

12/29/1024 Prokaryote Genomes- 1000’s of protein coding genes, most genes code for protein, only a small amount of non- coding DNA Eukaryote Genomes- 1000’s of protein coding genes, much of the genome does not code for proteins, many regulatory and repetitive regions

12/29/1025 Promoter- RNA polymerase attaches, to begin transcription Operator- small portion of DNA where an active repressor binds- when bound RNA polymerase cannot Structural Genes- one of many coding for amino acids that compose enzymes, transcribed as a unit Regulator Genes- located outside operon- controls whether or not an operon active or not.

12/29/1026 Trp operon- “turned on” unless too much of product is produced. Product can bind and change structure so that repression can bind

Lac operon- can be induced by product to “turn on” when needed 12/29/10

28 All cells contain the same genes. Some are turned on, some off. Different in each cell. Three different pathways:

12/29/1029 Chromatin structure- used to keep genes turned off, chromatin is more tightly wound in certain areas, it cannot be transcribed.

12/29/1030 Transcriptional- the number of times a gene is copied can be controlled by silencers or enhancers. mRNA can leave the nucleus at different rates, more mRNA more protein product.

12/29/1031 Translational- mRNA can be altered, so that it cannot be translated. The final polypeptide must fold correctly in order to be a functional protein.

12/29/1032 Within the DNA molecule genes are located on both sides of DNA helix, with one gene often overlapping another gene. Much of DNA coding is not well understood and introns may help control gene expression

12/29/1033 Transposons (jumping genes)- can alter gene expression. These genes can move around the genome and end up in the middle of a gene and prevent expression. Not well understood.

12/29/1034 Many coding genes are expressed only part of the time, controlled by some mechanism