Gene expression

DNA

Double stranded molecule, ATCG, deoxyribose sugar, permanent genetic code in nucleus, base order codes for genes/proteins, template strand is copied.

mRNA

Single stranded molecule, AUCG, ribose sugar, temporary copy of a gene, moves from nucleus to cytoplasm.

tRNA

Made of RNA, carries amino acids to ribosomes, anti codon pairs with mRNA codon, can be reused.

Codons

3 consecutive bases on mRNA

Anticodon

3 consecutive bases on tRNA, complementary to mRNA.

DNA triplets

are transcribed into mRNA codons.

Transcription

occurs in nucleus, it’s product in mRNA.

Transcription: Initiation

RNA polymerase enzyme binds to promotor sequence on DNA and unwinds it.

Transcription: Elongation

RNA polymerase builds mRNA strand by attaching RNA nucleotides to DNA template/anti-sense strand one by one by using complementary base pairing (U replaces T).

Transcription: Termination

RNA polymerase hits termination sequence and both it and mRNA deattach from DNA. Introns are spliced out, leaving exons to be expressed. mRNA is complete, it deattaches and moves out of nucleus pore into cytoplasm. DNA rewinds back up.

Translation

occurs in cytoplasm, uses mRNA to make proteins.

Translation: Initiation

mRNA is in cytoplasm. Ribosome will attach to start codon (AUG) of mRNA, tRNA brings amino acid.

Translation: Elongation

mRNA is read 1 codon at a time. Anticodon on tRNA binds with complementary codon on mRNA in ribosome. Amino acids attached to tRNA molecules sit beside one another. Peptide linkage forms between them. Ribosome moves along mRNA to next codon.

Translation: Termination

Continues until stop codons are reached. Polypeptide is released to be folded and modified by ER.

Mutation

Permanent change in the base sequence of DNA coding for a gene.

Point mutation

Mutation of a single base in gene at one point in DNA.

Substitution mutation

where 1 base in DNA gene sequence is substituted for another.

Insertion mutation (reading frameshift)

1 base in DNA base sequence is inserted.

Deletion mutation (reading frameshift)

1 base in DNA base sequence is deleted.

Substitution mutations

Missense, silent, nonsense.

Missense mutation

Substitution that results in a different amino acid being coded for. Protein may be dysfunctional.

Silent mutation

Point mutation leading to no change in amino acid coded for due to degeneracy of the code when several codons code for the same amino acid.

Nonsense mutation

Point mutation leads to STOP codon instead of an amino acid. Protein is dysfunctional.

Metabolic pathway

is a series of reactions controlled by enzymes where the product of one reaction becomes the substrate for the next reaction.

Precursor

Start of chain

Intermediates

substances being changed

Product

is the final substance.