eLFH - Gene transcription and translation Flashcards
Transcription definition
Process by which sequences of deoxyribonucleic acid templates produce specific messenger ribonucleic acid (mRNA) sequences
Translation definition
Process by which mRNA determines the final amino acid sequence via transfer ribonucleic acid (tRNA) within a ribosome
Process of transcription
Occurs in nucleus
Hydrogen bonds between DNA strands pulled apart as DNA is ‘unzipped’ by RNA polymerase enzyme
This creates a sense strand and anti-sense strand
Complementary RNA nucleotides are added to anti-sense strand to create mRNA via complementary nucleotide base pairing
mRNA processed to produce mature mRNA
Nucleotide categories
Purines
Pyrimidines
Purine nucleotides
Adenine (A)
Guanine (G)
Pyrimidine nucleotides
Cytosine (C)
Thymine (T) / Uracil (U)
Pairings between nucleotides
A <-> T / U
C <-> G
Transcription factors
Proteins that bind to specific DNA sequences
Either activators or repressors of RNA polymerase activity to regulate gene transcription to form mRNA
Translation process
mRNA crosses nucleus membrane into cytoplasm
mRNA reaches ribosome to be decoded
tRNA brings correct amino acid sequence to mRNA on ribosome via complementary base pairing
tRNA binds to P stie, then next tRNA binds to A site
P site amino acid binds to A site amino acid, ribosome shifts down by one codon and first tRNA is released
Process repeats until ribosome reaches stop codon where ribosome dissociates into subunits and releases mRNA and polypeptide chain
Components of 70s ribosome
Smaller 30s ribosome subunit
Larger 50s ribosome subunit
Binding sites on 70s ribosome
2 sites to which tRNA carrying amino acids can bind
P site (peptidyl site)
A site (acceptor site)
Codon definition
Sequence of 3 nucleotide bases which codes for a specific amino acid
Start codon and corresponding amino acid
AUG (if it is the first AUG codon of an mRNA)
Codes for Methionine
Stop codon examples
UAA
UAG
UGA
Direction of mRNA sequence translation from ribosome
5’ end to 3’ end
Anti-codon definition
Corresponding bases on tRNA which are complementary to the codon sequence on mRNA
Binding of amino acid to tRNA
Covalent bond at 3’ end
Enzymes responsible for loading tRNA with its amino acid
Aminoacyl tRNA synthetases
Number of codons
64
Number of amino acids
20
Most amino acids have more than one corresponding codon
Processing of polypeptide chains formed by translation
Polypeptide leaves ribosome
Goes to Golgi apparatus where it is processed and refined
Resultant protein is packaged and forms secretory granules
Proteins secreted from cell via exocytosis
Structure of polypeptides
Primary structure
Secondary structure
Tertiary structure
Quaternary structure (not all proteins have quaternary structure)
Primary structure of polypeptides
Sequence of amino acids formed is the primary structure
Amino acids linked via peptide bonds in a condensation reaction
Secondary structure of polypeptides
Polypeptide chain acquires geometric shape due to specific patterns of hydrogen bonds that form
Create either Alpha helices or Beta pleated sheets
Tertiary structure of polypeptides
Alpha helices or Beat pleated sheets fold to form 3D structures
Caused by various bonding arrangements
Quaternary structure of polypeptides
Occurs when more than one polypeptide join together
Not all proteins have quaternary structures
They form Fibrous or Globular proteins
Example of Globular protein with quaternary structure
Haemoglobin
Structure of Haemoglobin molecule
2 alpha polypeptide chains
2 beta polypeptide chains
Inorganic haem group per polypeptide chain containing Fe2+ ion
Abnormality in Sickle Cell Disease
Genetic mutation
Results in abnormal beta chains in Hb which protrude and hooks into neighbouring beta chain
Makes sickle cell Hb molecules lock together and precipitate out of solution
Crystal shapes are formed which leads to sickle shape of RBC
Types of genetic mutations
Insertion mutation - nucleotide base is inserted
Deletion mutation - nucleotide base is deleted
Substitution mutation - nucleotide base is replaced with another
Insertion and deletion mutations change all subsequent codons in the sequence until stop codon
Type of genetic mutation in sickle cell disease with codon change and amino acid change
Substitution mutation of one codon
GAG (glutamic acid) becomes GTG (valine)
Generic action of Oestrogen and Thyroid hormones
Hormones that affect DNA transcription via intracellular nuclear or cytoplasm receptors
Act as transcription factors
Slower to act than those hormones that affect cell membrane receptors
