Unit 5: Lesson 7 Flashcards
apoptosis
- programmed cell death
- cell shrinks, cell parts are packaged into vesicles which are engulfed and digested by scavenger cells
Apoptosis in embryonic development; C.elegans
-a death cell inactivates Ced-9 allowing Ced-4 and Ced-3 to activate, leading to activation of other proteases and nucleases (enzymes that cause the changes seen in apoptosis)
Initiating Apoptosis
- mitochondrial proteins triggered to from pores which cause leakage and release of apoptosis promoting proteins
- death ligand binds to surface receptor, leading to activation of capases (enzymes which carry out apoptosis)
- damaged nucleus or misfolded ER can also send death signal
Apoptosis is essential for:
normal development of vertebral nervous systems, operation of immune system, normal morphogenesis
histone acetylation
neutralizes histones so they do not bind to neighbors. Results in looser structure and easier access to genes
-enzymes involved may also bind to and recruit components of transcription machinery
histone methylation
- promotes condensation of chromosomes
- phosphate next to methyl causes loosening
epigenetic inheritance
inheritance of traits transmitted by mechanisms not directly involving the nucleotide sequence
Eukaryotic Gene transcription
- transcription initiation complex (proteins, RNA polymerase II) assembles on promoter
- RNA polymerase II synthesizes pre-RNA
- RNA processing: adds 5’ cap and 3’ tail, introns removed
General transcription factors
bind to DNA or other proteins, forming an initiation complex that produces a low level of transcription
Specific Transcription factors
- can greatly increase or decrease rate of gene expression by binding to the distal control elements of the enhancer
- can also recruit proteins that acetylate or deacetylate histones
activators
- Bind to control element
- DNA bends bringing activators closer to the promoter
- bind to mediator proteins and general transcription factors, helping form a transcription initiation complex on promoter
repressors
-can bind to control element or block binding of activators to proteins that let activators bind to DNA
Coordinately controlled genes
- dispersed but have a specific combination of control elements
- a chemical signal produces/activates a particular transcription activator or repressor
alternative RNA splicing
-depends on regulatory proteins that bind to regulatory sequences, which choose which segments are treated as exons and which as introns
mRNA degredation
lifespan of mRNA in cytoplasm (controlled by untranslated nucleotide sequences) plays a role in pattern of protein synthesis
- if short can change quickly
Initiation of translation
- regulatory proteins may bind to untranslated region of ends, preventing ribosome attachment
- in eggs, poly-A tails may be too short, but at the appropriate time Adenine nucleotides are added
- activation or inactivation of required protein factors can regulate translation of all mRNA’s simultaneously