Biology - Protein Synthesis

central dogma of biology

the theory that genetic information flows only in one direction, from DNA to RNA to protein

protein synthesis flow chart

dna (transcription) —> premRNA —> mRNA (translation) —> protein —> protein folding

transcription

the process by which a DNA gene is copied onto a messenger (mRNA)

• occurs in the nucleus

translation

the process of which an mRNA message is “read” by the ribosome (RER) and corresponding amino acids are brought to the ribosome by transfer RNA (tRNA)

• occurs in the cytoplasm

mRNA processing before it leaves the nucleus

1. protect the message

   1. a modified guanine is attached to the 5’ end (guanine cap) to protect from digestive enzymes in the cytoplasm

   2. many adenines (As) are added to the 3’ end of the pre-mRNA (poly-A-tail) to act as a “fuse” to ensure the mRNA is not permanent

      1. to not overproduce proteins

2. refine the message

   1. spliceosome (scissor like protein) cuts out introns (non-coding sequences) and leaves behind exons (coding sequences)

3. maximize the message

   1. the spliceosome can cut out exons in creating different proteins from the same gene

      1. "“alternative splicing” to create similar not same proteins

      2. can create hundred thousand proteins from 20k genes

base pair substitutions

1. silent: a mutation occurs for the same amino acid as the original dna

   1. UGU = UGC = cys —> no effect

2. missense: a mutation codes for the wrong amino acid

   1. UGU —> UGG (not equal) can be harmful, can be harmless

3. nonsense: a mutation codes for a premature stop

   1. UGU —> UGA = stop —> very harmful

insertions or deletions of one or more bases

1. frameshift: the entire reading frame is shifted by the addition or deletion of a non-three number of bases (since read in threes)

   1. SERIOUS

   2. ABC|ZDE|F

2. non-frameshift: insertion or deletion of 3 or a multiple of 3 bases

   1. could be serious, could be not serious

   2. ABC|XYZ|DEF

RNA Polymerase

• makes RNA? —> synthesizes RNA

• makes RNA chains complementary to DNA strands