Gene Regulation and Protein Synthesis Flashcards
Central Dogma
Flow of genetic information from DNA towards protein
Location of Gene expression in Prokaryotes and Eukaryotes
Prokaryotes - within cytoplasm
Eukaryotes - from nucleus to cytoplasm
Codon-Anticodon Base Pairing
tRNA anticodons form base pairs with mRNA codons
3 nucleotides - triplet
Reading frames
How a nucleotide sequence is divided up.
Can be read in different ways, hence giving different amino acids
Depends on translation start site
Translation Components (7)
Amino acids
tRNAs
Aminoacyl-tRNA-synthetases
Protein factors
Energy source - ATP/GTP
Ribosome (large and small subunits)
mRNA
Aminoacyl-tRNA synthetases
Bind amino acids to specific tRNA using ATP
Ribosomes - Subunits, Binding sites
4 rRNA molecules and protein components
3 binding sites (EPA)
Initiation - Translation
Requires initiation factors
GTP hydrolysed
Small ribosomal subunit binds to 5’ mRNA end
Start codon - methionine
Large subunit joins assembly and initiator tRNA is located in P site
Elongation - Translation
Elongation factor (EF-1a) brings next aminoacyl-tRNA to the A site
GTP hydrolysed, EF released from tRNA
Second elongation factor regenerates EF-1a
Termination - Translation
Stop codon (UAA, UAG, UGA
No aminoacyl-tRNA base pairs with stop codon
Release factor binds stop codon
FInished protein cleaved off tRNA
Dissociation of RNA molecules (3)
Peptide bond formation and translocation
Peptidyl transferase catalyses peptide bond formation between amino acids in P and A sites
EF-2 moves ribosome along mRNA
Empty tRNA moves to E site
tRNA with growing peptide moves from A to P site
A site is free
Polysome
Multiple regions of translation
Types of Mutations (5)
Point mutation - change single base
Missense mutation - change in amino acid sequence, change function
Nonsense mutation - new termination codon, change protein length
Silent mutation - no change in amino acid sequence, due to degeneracy, no effect on function
Frameshift mutation - addition/deletion of single base, change reading frame
Chromosomal Mutations (4)
Deletions
Duplications
Inversions
Translocations
What happens with the finished protein? (3)
Targeting
Modification
Degradation
Free and Bound Ribosomes
Free Ribosome - cytosol, proteins destined for cytosol, nucleus, mitochondria, translocated post-transitionally
Bound RIbosomes - rough ER, proteins destined for membrane, ER, Golgi, secretion, translocated co-translationally
Post-Translational Modifications
Phosphorylation
Acetylation
Methylation
Glycosylation
Disulphide bridges
Ubiquitinylation
BREAK
RNA
Single stranded
Stem loops sometimes
3 classes - rRNA, tRNA, mRNA
tRNA
Adapters between nucleic acid code and amino acid code
Anticodon
Attach to 3’ end
Cloverleaf structure
mRNA
tRNA
Transcription
RNA polymerase binding
DNA chain separation
Transcription initiation
Elongation
Termination
Promoters
RNA Polymerase II specific promoter
Transcription = +1
TATA box = -25
TATA box binding protein
Recognises TATA box
Complex with TFIID (general TF)
Introduces kink into DNA - determines transcriptional start and direction
Initiation - Transcription
Additional general TFs
Ordered - TFIID/TBP –> TFIIB –> TFIIF + RNA Pol I –> TFIIE + TFIIH
RNA Pol II & TFIIF extend transcript on their own
TFIID remains at pronoter
Elongation - Transcription
Transcription bubble - one direction
DNA unwound and rewound behind RNA Pol II
5’ to 3’
Complementary to template
Termination - Transcription
Newly synthesised RNA makes stem-loop structure - followed by Us
RNA cleavage
Specific Regulation of Transcription
Specific TFs –> DNA-binding proteins (2 functional domains)
Enhancers & Silencers - long stretches of DNA between binding site and transcription complex
Coordinated Gene Expression
Specific stimuli
Regulatory protein
Bind to Response elements of multiple genes
Produce different proteins
Steroid Receptors
Family of TFs
Domains - DNA-binding and ligand-binding
Ligand binding –> Move to nucleus –> Bind to SREs
Glucocorticoid Receptor
Steroids transported in blood
Free steroids bind to steroid receptor –> Receptor translocates to nucleus –> Binds to response elements –> Coordination regulation
Exons and Introns
Exons = Coding Regions
Introns = Non-coding Regions
Transcribed together
Introns removed (splicing)
Ends of mRNAs
5’cap
Poly(A) tail
