AP Bio - Unit 6: Gene Expression and BioTechnology (Gene Expression)

Central Dogma of Molecular Biology

**DNA >** *transcription* **> RNA >** *translation* **> Protein**

explanation of the flow of genetic information

RNA Polymerase

makes mRNA from DNA

mRNA

messenger RNA, Hold copy of DNA in RNA form for sequencing outside of the nucleus

mRNA editing steps

1. mRNA has to parts, exons and introns
2. in nucleus, SPLICOSOME COMPLEX makes cuts in mRNA
3. introns are removed and exons are kept, mRNA is now “mature”


1. a “poly-a tail” is added to the 3’ end and a GTP5 cap is added on the 5’ end

poly-a tail function

attached to the 3’ end of mRNA to slow down the destruction of mRNA in the cytoplasm

GTP5 cap funtion

guides mRNA to destination and helps it to leave the nucleus

ribosome function

reads mRNA **5’>3’** in codons (nucleotide triplets)

uses EPA complex (arrival, processing, exit)

Start/Stop codons

Start: AUG (makes amino acid)

Stop: UAA, UAG, UGA (no amino acid)

tRNA

transfer RNA, contain amino acid and anti-codon (matches with mRNA) and helps to build poly-peptide chain. made in nucleolus

Mutation

any change in genes, not always bad

mutation at DNA level: significant impact

mutation at RNA level: minor impact but more likely because of lack of “proofreading”

mutation to somate cells isnt passed on, mutation to germ cells is passed to offspring

causes of mutation

induced (outside factor) or spontaneous (copying error)

induced mutation example

radiation, chemicals, infectious agents

spontaneous mutation examples

DNA copying, alternative splicing

types of mutations

silent, missense, frame shift, nonsense (from least to most impactful)

silent mutation

nucleotide is changed but amino acid product isnt affected

missense mutation

one amino acid in change but the rest remain the same

frame shift mutation

insertion or deletion of nucleotide that shifts the “reading frame” of the ribosome.

nonsense mutation

missense or frame shift mutation that results in a premature stop codon