Biology Test Review 

DNA Introduction

  • Genetics - the study of genes and heredity
  • Trait - inherited characteristics
  • Gene - a segment of DNA that codes for a protein, which codes for a trait
  • Chromosomes - made of DNA, located in the nucleus

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DNA

  • Deoxyribonucleic Acid
  • Called the blueprint of life
  • Monomer: nucleotides
  • Sugar: deoxyribose
  • Location: nucleus only
  • Bases: adenine, guanine, cytosine, thymine
  • Structure discovered by Watson and Crick
  • Essential to all life on earth

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Nucleotide

  • Monomers of DNA and RNA
  • Consists of a phosphate group, sugar and base
  • Sugar for DNA - deoxyribose
  • Sugar for RNA - ribose
  • Bases for DNA - A, C, G, T
  • Bases for RNA - A, C, G, U
  • Purines - double ringed structure, Adenine and Guanine
  • Pyrimidines - single ringed structure, Cytosine, Thymine, and Uracil
  • Base pair rule: Adenine bonds with Thymine, Cytosine bonds with Guanine

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DNA Structure

  • Shape: double helix
  • Double stranded
  • Sides of the DNA ladder made of phosphate and sugar
  • Rungs of the DNA ladder made of nitrogenous bases bonded with hydrogen bonds
  • Adenine bonds with Thymine
  • Cytosine bonds with Guanine

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RNA

  • Ribonucleic Acid
  • Monomer: nucleotides
  • Sugar: ribose
  • Bases: adenine, guanine, cytosine, uracil
  • Location: in and out of nucleus
  • Single stranded
  • Types of RNA
    • mRNA - messenger RNA - gets the message from DNA in the nucleus and brings the codons to the ribosomes in the cytoplasm
    • tRNA - brings the anticodon to the ribosomes and the matching amino acids to the mRNA codons
    • rRNA - makes up the ribosomes - responsible for protein synthesis

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DNA Replication

  • Process by which DNA makes a copy of itself
  • DNA helicase breaks the hydrogen bonds to begin replication
  • DNA polymerase brings the nucleotides to the exposed bases, checks for errors in nucleotide pairing
  • DNA ligase zips the new DNA back together

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Transcription

  • DNA message is converted into an RNA molecule
  • RNA polymerase unzips the DNA molecule and mRNA strand is formed complementary to the DNA bases
  • Occurs in the nucleus
  • Adenine bonds to Uracil in transcription

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Translation

  • mRNA leaves the nucleus containing the instructions for protein synthesis
  • mRNA brings a strand of codons (3 bases) to the ribosome
  • tRNA meets mRNA with the anticodons
  • tRNA brings the amino acid that matched the mRNA codon
  • Occurs on the ribosomes in the cytoplasm

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Mutations

  • Changes in the nucleotide sequence
  • Occurs in somatic cells and gametes
  • Mutations happen regularly, most are neutral, and many are repaired by enzymes
  • Some mutations improve an organism's survival
  • Chromosome mutations
    • Deletion - due to breakage, a piece of a chromosome is lost
    • Inversion - segment breaks off, flips around and reattaches
    • Duplication - when a gene sequence is repeated
    • Translocation - involves two chromosome, part of one chromosome is transferred to another chromosome
    • Nondisjunction - failure of chromosomes to separate during meiosis, occurs in gametes only, gametes may have too many or two few chromosomes

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  • Gene mutations
    • Change in the nucleotide sequence
    • May only involve a single nucleotide
    • Point mutation - change of a single nucleotide, deletion, insertion or substitution of ONE nucleotide in a gene
    • Frameshift mutation - Inserting or deleting one or more nucleotides, changes the reading frame, results in proteins built incorrectly
    • Substitution - one base pairs is replaced by another
    • Insertion - one or more base pairs is added to a sequence
    • Deletion - one or more base pairs is lost from a sequence

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Mutation Results

  • Silent mutation - when a base pair is substituted but the change still codes for the same amino acid
  • Substitution - when a base prairie is substituted and the new codon codes for a different amino acid
    • If the substitution changes the amino acid, it’s called a missense mutation (this change is responsible for new variations of a trait)
    • If the substitution does not change the amino acid, it's called a silent mutation (this change does not result in any amino acid differences)
    • If the substitution changes the amino acid to a stop, it's called a nonsense mutation (this change stops the translation of an mRNA molecule)
  • Premature stop - when a substitution results in the formation of a STOP codon before all of the codons have been read and translated
  • Codon deletion or insertion - a whole new amino acid is added or missing
  • Frame shift - when a deletion or insertion results in a different base pair at the beginning of the next codon, ching the whole sequence of amino acid

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