Chp 3

Cards (77)

  • nucleic acids are large biomolecules that store and transmit hereditary information
  • DNA:
    • carries instructions that code for RNA
    • can self replicate
    • stores and transmits hereditary information
  • RNA:
    • has different forms (rRNA, tRNA, mRNA)
    • read and translate DNA information (tRNA)
  • nucleotides have three basic units:
    • phosphate group
    • five-carbon sugar (deoxyribose in DNA, ribose in RNA)
    • a nitrogenous base (A,G,C,T,U)
  • Purines are nitrogenous bases with two rings in their structure
    • adenine
    • guanine
  • pyrimidines are nitrogenous bases with one ring in their structure
    • thymine
    • uracil
    • cytosine
  • complementary base pairs
    • adenine and thymine/uracil (joined by two weak hydrogen bonds)
    • guanine and cytosine (joined by three hydrogen bonds)
  • DNA is a long, coiled, double-stranded nucleic acid that forms a double helix
  • RNA is single stranded and are shorter than DNA molecules
  • histones are proteins in eukaryotic cells that tightly package DNA into structures called nucleosomes
  • nucleic acids are made up of nucleotides
  • in DNA the 5 prime end is up and the 3 prime end is down and the double strands are antiparallel
  • anticodons pair with mRNA codons
  • genes are region sof DNA that may be translated into a polypeptide or an RNA molecule that can be functional
  • the genetic code is a set of rules that defines how the information in nucleic acids is translated into proteins and functional RNA molecules
  • transcription is the production of single-stranded mRNA from DNA
  • translation is the process where the sequence of an mRNA molecule is used to produce the amino acid sequence of a polypeptide
  • the genetic code is degenerate because more than one codon can code for the same amino acid - the genetic code uses 4 nucleotides while 3 nucleotides code for an amino acid
  • structure of eukaryotic genes
    • promoter region
    • exons
    • introns
  • promoter regions are upstream binding regions where RNA polymerase attaches to the gene
  • exons are coding regions of DNA
  • introns are non-coding regions of DNA
  • RNA polymerase is needed to separate the double helix in a small section of DNA
  • gene expression is the process where the information stored in a gene is used to synthesise a functional gene product (RNA or a protein)
  • triplets are a sequence of 3 nucleotides in genes that corresponds to a specific amino acid in a polypeptide chain
  • universal - the same triplet will code for the same amino acid in almost all organisms
  • ribosomal RNA is a structural component of ribosomes
  • messenger RNA (mRNA) is a single stranded molecule that carries the information from the DNA to the ribosome
  • transfer RNA bring amino acids in the order specified by the mRNA and rRNA to the ribosomes to help build a polypeptide chain
  • Protein synthesis has three phases
    • transcription
    • RNA processing
    • translation
  • Transcription has three phases
    • initiation - RNA polymerase attaches to the promoter and begins unwinding the double helix, this strand is complementary to te non-template strand (coding strand)
    • elongation - moving in a 3' to 5' direction, RNA polymerase catalyses condensation polymerisation of free m RNA nucleotides, DNA triplets are being transcribed into RNA codons
    • termination when RNA polymerase hots the stop codon the mRNA transcript detaches from the RNA polymerase
  • RNA processing has two steps:
    • addition of a 5' cap and a poly-A tail to the 5' and 3' end of the pre-mRNA
    • splicing - introns are removed and exons are spliced together, the mature mRNA moves into the cytoplasm
  • Transcription and RNA processing occurs in the nucleus and translation occurs in the cytoplasm in a ribosome
  • Translation has three stages:
  • Initiation:
    • Ribosomal subunit attaches to the 5' end of the mRNA molecule and moves along until it finds the start codon
    • A loaded tRNA molecule with the anti-codon attaches to the codon
    • A large ribosomal subunit attaches to the tRNA and the small ribosomal subunit
  • Elongation:
    • Another loaded tRNA molecule with an anticodon for the next triplet on the mRNA molecule attaches
    • Amino acids form a hydrogen bond to create a growing polypeptide chain
    • Unloaded tRNA molecule with the anticodon detaches and leaves
  • Termination:
    • Polypeptide chain continues to form until a stop codon is reached
    • The polypeptide chain is released from the ribosome
  • alternative splicing is when different combinations of exons form different proteins when some exons are spliced along with the introns
  • there are three sites for tRNA to bind, aminoacyl site, peptidyl site, exit site
  • gene expression in eukaryotes can be regulated at any stage of the three stages