Unit 5 Molecular Genetics SG PDF

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Summary

This is a compilation of notes from the Molecular Genetics Unit of AP Biology (Can be used to study for one particular test and for the AP as a whole)...

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Unit 5: Molecular Genetics Study Guide

information from DNA to protein -

the DNA genotype is expressed as proteins, which provide the molecular basis for phenotypic traits DNA in the nucleus to RNA and RNA in the cytoplasm to protein Transcription is the synthesis of RNA under the direction of DNA Translation is the synthesis of proteins under the direction of mRNA

chromosomes, genes, alleles, DNA sequences, and mutations -

sequence: a series of nucleotide bases chromosome: single long DNA molecule allele: different versions of the same gene genome: all DNA collectively gene: section of a chromosome the encodes a single polypeptide mutation: random changes in DNA sequence

RNA -

RNA -

uses sugar ribose instead of deoxyribose has U instead of T RNA is usually single-stranded unlike DNA it can be coding or non-coding - mRNA used to bring gene sequences to ribosomes for translation into proteins - ncRNA has many protein functions (acting as enzymes, regulating gene expression, and forming structural molecules)

purine and pyrimidine bases -

pyrimidines: single ring structures (T, C) purines: double ring structures (A, G) general structure of DNA - phosphate group, sugar, nitrogenous base 3 H bonds between G and C 2 H bonds between A and T

DNA and RNA structure/synthesis

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DNA can only replicate in the direction of 5’ to 3’ because of the way each nucleotide is structured - phosphate group, 5 carbon sugar, and a nitrogenous base this means that strands in DNA run in opposite directions and can only build in those directions - DNA and RNA are always built by adding new nucleotides to the 3’ end of the strand

DNA replication -

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the two DNA strands separate each strand is used as a pattern to produce a complementary strand semiconservative: each new DNA helix one old strand with a new strand continuously - this means that the DNA can be built without stopping in between and it means that its being build on the leading strand (from 5’ to 3’) discontinuously - the DNA can only be built by moving the primer backward since the DNA is being built on the lagging strand, (from 3’ to 5’) - pieces are known as Okazaki fragments

RNA primers in DNA replication -

without them, DNA cannot be built once a primer is placed, DNA polymerase comes in and builds the DNA - at the end, the primer is removed and replaced with DNA

functions of the enzymes in DNA -

helicase: unwinds the DNA topoisomerase: makes sure the DNA ahead does not get twisted DNA polymerase: adds nucleotides to the 3’ end of the growing chain and proofreads/corrects improper base pairings DNA ligase: joins small fragments into a continuous chain

DNA damage and repair mechanisms -

nucleotide excision repair - enzymes cut out and replace damaged stretches of DNA (have to be done before the DNA is replicated again or before it is permanent)

DNA transcription and translation -

transcription: produces genetic messages in the form of RNA - initiation: RNA polymerase attaches to the promoter - elongation: RNA grows longer - termination: RNA polymerase reaches a sequence that indicates termination

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translation: the process of ribosomes reading mRNA and producing the polypeptide - involves two types of RNA - rRNA: combines with protein to form a ribosome - tRNA: reads mRNA - occurs on the surface of a ribosome - has two units: small subunit and large subunit - ribosomes have binding sites for mRNAs and tRNAs - process - initiation: establishes where the translation will begin (AUG codon) - elongation: adds amino acids to the polypeptide chain until a STOP codon - termination: same

post-translational modifications -

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a poly-A tail (3’) and nucleotide cap (5’) are added to the ends of mRNA - allow transport, protect from enzymes, help ribosome attach eukaryotic genes contain non-coding sequences (introns) and coding sequences (exons) - transcription copies all introns and exons, but introns are later spliced out before the mRNA can be used by the ribosome alternative splicing: different mRNA sequences can be made from the same gene sequence

genetic code -

three nucleotides (triplet/codon) encode one amino acid - more than one triplet encodes the same amino acid → “redundant” - reduces the chance of mutation having an effect

mutations -

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causes - occur when DNA is copied and the mistake is not fixed (the repairing is not done before it becomes permanent) - continues in further generations - mutagenic chemicals: directly trashes DNA or interferes with replication - carcinogens: prone to mutating oncogenes - radiation: can fuse holes or knock holes in DNA - viruses: insert their DNA directly into the host types - single nucleotide changes - point mutations include insertion, deletion, substitution - silent mutation: the amino acid is not affected by the change - missense: substitution, codes for different amino acid - nonsense: changes normal codon to stop codon - frame shift: nucleotide gets added/deleted, entire code changes (VERY BAD)

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effects - the RNA copy has the wrong instructions → makes the protein incorrectly (could lead to either a malfunctioning protein or an improved protein)

beneficial mutations -

sickle-cell disease protects against malaria light skin color improves survivability into low-light environments by having the ability to make more vitamin D

how do eukaryotic genes differ from prokaryotic genes -

eukaryotic genes contain non-coding sequences (introns) and coding sequences (exons) - transcription copies all introns and exons, but introns are later spliced out before the mRNA can be used by the ribosome...