ap bio unit 6 gene expression and regulation

messenger RNA (mRNA)

single stranded sequence of RNA nucleotides; RNA copy of a gene that carries instructions from nucleus to ribosome

transfer RNA (tRNA)

T-shaped structure made of RNA nucleotides; amino acids are attached on top & anticodons are attached on bottom loop; carry amino acids to ribosomes during translation and transfer them to growing polypeptide chain

ribosomal RNA (rRNA)

sequence of RNA nucleotides that bind to ribosomal proteins to form whole ribosome; assists with translation of mRNA

5’ cap

specially modified guanine nucleotide that’s added to 5’ end of transcript; protects mRNA from degradation in cytoplasm + helps ribosome bind at mRNA start codon to initiate translation

poly A tail / GTP cap

series of A nucleotides added to 3’ end of transcript; aids in nuclear export, protects mRNA from degradation in cytoplasm, helps ribosome bind at mRNA start codon to initiate translation

exons

sequences of mRNA that actually code for part of proteins

introns

sequences of mRNA that exist between exons + allow for alternative splicing

alternative splicing

introns are removed and exons are joined together to form mature mRNA; protein diversity + regulate gene expression

codon

sets of 3 nucleotides; in translation, mRNA is read from 5’ to 3’ in codons; ribosome starts at AUG and ends at stop codon

gene regulation

processes in which organisms control which genes are being expressed; allows differential gene expression in eukaryotes + prokaryotes cells

eukaryotic gene regulation

eukaryotic genes are grouped together + activated by same transcription factors; allows for complementary to be activated at same time

prokaryotic gene regulation

prokaryotes organize genes into transcriptional units (operons)

operons

closely linked genes that produce a single mRNA molecule during transcription; turn genes on and off; components are promoter, operator, genes, regulatory proteins

regulatory sequence

regulate transcription, don’t code for proteins, allow for positive + negative control of transcription, don’t need to be close to the gene

positive regulatory sequences

increase gene expression + proteins that come from the gene (promoter + enhancer sequences)

promoter sequence

sequences upstream (near 5’ end) of transcription start site where RNA polymerase + transcription factors (regulatory proteins) bind to initiate transcription

enhancer sequences

can occur upstream or downstream (5’ or 3’) of a gene; activator protein binds to them; increases amount of mRNA produced

negative regulatory molecules

inhibit gene expression by binding to DNA + blocking transcription (repressor proteins + silencer sequences)

gene regulation importance to homeostasis

fine-tune how much of a protein is made at a given time in responses to changes in environment

eukaryotic transcription location

nucleus (where DNA is stored)

eukaryotic translation location

cytoplasm

prokaryotic transcription and translation location

both cytoplasm

mutations

random changes in DNA sequence; most have no effect on organisms; negative or positive are very rare

reading frame

sequence of nucleotides that code for protein + are “read” by ribosomes; mutations to reading frame sequences can cause a protein to change in structure, preventing protein from functioning

central dogma of bio

DNA (transcription) → RNA (translation) → protein

point mutations

a change in 1 to 3 nucleotides + only affect 1 gene; occur during DNA synthesis in cell cycle

chromosomal mutations

affect big sections of chromosomes + many genes; occurs during meiosis

substitution mutation

point mutation where original nucleotide is replaced by a different nucleotide

silent substitution mutation

change in a single nucleotide that doesn’t result in a change in amino acid sequence

missense substitution mutation

change in a single nucleotide that results in a change in a single amino acid in the sequence

nonsense mutation

change in a single nucleotide that results in a premature stop-codon in mRNA sequence; codons after stop-codon won’t be translated; protein won’t have all of its amino acids so it won’t fold or function properly

frameshift mutation

addition or removal of a single nucleotide changes the reading frame for protein; always negative affect

insertion mutation

insertion of a single nucleotide into DNA sequence; protein won’t fold or function correctly

deletion mutation

deletion of a single nucleotide into DNA sequence; protein won’t fold or function correctly