u3aos1

Cards (58)

  • Nucleic acids
    Information storage molecules present in all living things
  • Nucleic acids
    Determine how an organism functions by coding for proteins
  • Function of nucleic acids
    1. DNA is copied into mRNA
    2. mRNA is read at the ribosome to make a protein
    3. Genes are switched on and off depending on needs of cell
    4. As protein is made it folds depending on order of amino acids
    5. Some proteins are processed and secreted from the cell
  • Nucleotide
    Monomer of a nucleic acid, has 3 components: phosphate, sugar, nitrogenous base
  • Nucleotide
    • In DNA: Thymine, Adenine, Cytosine, Guanine
    • In RNA: Uracil, Adenine, Cytosine, Guanine
  • Polynucleotide strand
    1. Nucleotides are bonded together via phosphodiester bonds
    2. Bases are attracted to other complementary bases via hydrogen bonds
  • Nucleic acids
    • Deoxyribonucleic acid (DNA)
    • Ribonucleic acid (RNA): messenger RNA (mRNA), transfer RNA (tRNA), ribosomal RNA (rRNA)
  • DNA vs RNA
    • DNA is double stranded, RNA is single stranded
    • DNA sugar is deoxyribose, RNA sugar is ribose
    • DNA bases are C, G, T, A, RNA bases are C, G, U, A
  • Nucleic acid structure
    1. Adenine (A) bonds to Thymine (T)
    2. Guanine (G) bonds to Cytosine (C) - complementary base pairing
  • Function of DNA
    • In prokaryotes, DNA is organised into a single circular chromosome
    • Some DNA is also found as small circular pieces of DNA called plasmids
    • In eukaryotes, DNA is organised into linear chromosomes, contained within the nucleus
  • Eukaryotic DNA
    • One chromosome = One DNA molecule (neatly packed)
    • Some DNA is also found as small circular chromosomes in mitochondria and chloroplasts
  • Genome
    The complete sequence of DNA in a single set of an organism's chromosomes
  • Gene
    Sequences of DNA that code for a protein
  • Allele
    Different versions of the same gene
  • Function of nucleic acids
    DNA is confined to the nucleus, so an RNA copy (mRNA) is made to carry the information to the ribosome for protein synthesis
  • Transcription
    The process of copying the coding region of a gene into mobile mRNA
  • Transcription - step by step
    1. Promoter signals start of gene
    2. RNA polymerase binds to promoter and unwinds DNA
    3. Complementary RNA nucleotides are joined to form pre-mRNA
    4. Stop signal releases pre-mRNA
    5. DNA zips back up
  • Introns
    Interruptions in the sequence (non-coding regions), cut out of pre-mRNA
  • Exons
    Coding regions, spliced together
  • Post-transcriptional modifications
    1. Methylated cap added to 5' end
    2. Poly-A tail added to 3' end
    3. Introns cut out
  • Codon
    Set of 3 bases in mRNA that codes for an amino acid
  • Translation
    1. mRNA attaches to ribosome in cytoplasm
    2. Ribosome made of rRNA and proteins
    3. tRNA carries amino acids to ribosome
  • Translation - Initiation
    1. Small ribosomal subunit binds to mRNA and moves to start codon (AUG)
    2. tRNA with appropriate anticodon aligns with start codon
    3. Large ribosomal subunit aligns with tRNA
  • Translation - Elongation
    1. Second tRNA molecule pairs with next codon
    2. Amino acids are added to growing polypeptide chain via peptide bonds
    3. Ribosome moves along mRNA one codon at a time
  • Translation - Termination
    1. Elongation continues until ribosome reaches stop codon
    2. Polypeptide is released and ribosome disassembles
    3. Polypeptide may undergo post-translational modification
  • Amino acids will not start being joined together until an AUG start codon
  • Translation - Elongation
    One codon position and the next complementary tRNA molecule is able to bind, carrying in another amino acid which is added to the growing polypeptide chain
  • Translation - Termination
    1. Elongation continues until the ribosome reaches a stop codon
    2. These codons do not code for any amino acids and instead signal for translation to stop
    3. The polypeptide is released and the ribosome disassembles back into subunits
    4. The polypeptide may undergo post-translational modification prior to becoming a functional protein
    5. Multiple ribosomes can translate a single mRNA sequence simultaneously (forming polysomes)
  • Amino acid sequences
    • AUGGCCGUAUCAGUUUGA
    • GCAAUGGGGCAGUAACUU
  • The human genome contains about 20,000 to 25,000 genes (typical of other mammals) although the total number of proteins in a human cell is estimated to be between 250,000 – one million
  • In the past it was accepted that one gene had a single function – i.e. coded for only one protein
  • Research is showing that one gene can be regulated in different ways so that it can produce more than one protein
  • One gene could produce different proteins at different stages of development
    One gene could produce different proteins in different tissues
  • Alternative splicing of pre-mRNA
    1. One way is through alternative splicing of the pre-mRNA molecules from a single gene
    2. Intron retention can produce different mRNA molecules from the same pre-mRNA, i.e. different numbers of introns are cut out and discarded
    3. Intron jugglingintrons are spliced together differently
  • The monomer (subunit) of a protein is an amino acid
  • Amino acids are joined together during translation by peptide bonds

    In the process a water molecule is released
  • Amino acids
    • There are 20 different amino acids. They all have the same base structure with a different side group (R group)
  • Polar, hydrophilic regions

    Amino acids with these R groups are generally found on the surface of the protein as they are able to interact with the aqueous environment both inside and outside the cell
  • Non-polar, hydrophobic regions
    Amino acids with these R groups are generally found folded within the protein
  • Levels of protein structure
    • Primary structure
    • Secondary structure
    • Tertiary structure
    • Quaternary structure