genes
translation
protein synthesis
eukaryotes regulate gene expression...
before, during, and after transcription and RNA processing
prokaryotic translation
occurs as mRNA is being made by RNA polymerase
Prokaryotes regulate gene expression at....
the transcription level
operon
contains all the genes needed for a singles biochemical pathway
phosphate groups
can act as tags to modify histones and control availability of DNA for transcription
chromatin
refers to how tightly packed the nucleosomes are
lac operon
indicible operon in prokaryotes
euchromatin
areas of DNA that are available for transcription; not tightly packed
lactose
an alternative energy source for bacteria; but bacteria prefer to use glucose for energy
heterochromatin
areas of DNA that are tightly packed and not available for transcription; dark patches in the nucleus
RNA polymerase
required for transcription of eukaryotic genes; require presence of transcription factors to initiate transcription
what has to happen before translation can be initiated
RNA polymerase must wait for specific transcription factors that bound to distal control elements to interact with PIC
what happens when PIC is activated by distal control elements
RNA polymerase begins transcribing the gene; simultaneously, the TBP releases from promoter region
when is lactose absent
lac repressor binds to lac operator and transcription of lac operon is blocked
post-transcriptional regulation (eukaryotes)
immediately after transcription, RNA molecule is known as a pre-mRNA; pre-mRNA must undergo processing in nucleus before it becomes mature mRNA and before it can be exported from nucleus
RNA splicing
first stage of post-transcriptional regulation; pre-mRNA still contains introns, that must be spliced out of RNA; requires proper identification of introns; Errors in splicing could lead to splicing-out an exon that is needed
RNA splicing errors q
can be deleterious to organism or cell; it is possible for them to produce a protein variant - without loss of original protein function; new variants might bestow an adaptive advantage
alternative RNA splicing
some genes can undergo this during post-translational modification, including: exon skipping, mutually exclusive exons, alternative 5' donor sites; alternative 3' donor sites, and intron retention; leads to possibility of one gene to multiple gene products
when is lactose present
lac repressor protein binds to lactose, which causes it to change shape so that lac operon is turned on and transcription occurs at low rate until cAMP/CAP complex binds to it
transcription in eukaryotes
1. Initiation: formation of pre initiation complex; interaction of specific transcription factors with general transcription factors and RNA polymerase II
2. Elongation: Production of pre-mRNA and RNA polymerase II
3. Termination: release of pre-mRNA and RNA polymerase II upon reaching termination sequences in gene
forming the pre-initiation complex (PIC)
TATA-binding protein (TBP) binds to TATA box; Binding of TBP causes transcription factor IID (TFIID) complex to be recruited to promoter region; This causes host of general transcription factors (TF's) to be recruited to promoter region; When all general transcription factors are bound to promoter region, RNA polymerase is recruited and binds; when all general transcription factors and RNA polymerase are bound to promoter region, PIC is formed
gene production
1. RNAs: mRNA, tRNA, rRNA, other RNAs
2. polymers of amino acids:
peptides-generally refer to small (short) polymers of amino acids
polypeptides- Generally refers to longer (larger) polymers of amino acids. Often used when talking about protein subunits
protein- refers to functional and mature gene product, it may be made of single strand of amino acids, or it may have multiple peptide subunits
basics of gene expression in prokaryotes
lack nucleus; DNA found in cytoplasm; transcription and translation occur at the same time; gene expression is regulated at transcription; genes organized in operons; have circular chromosomes made of double stranded DNA
basics of expression in eukaryotes
have nucleus; DNA confined to nucleus, mitochondria, plastids; have multiple linear chromosome; temporal and spatial separation of transcription and translation; regulated at multiple levels