Tumour suppressor protein phosphorylated by CDK enzyme
E2F
Transcription factor stimulated by phosphorylation of Rb
Cyclin D1 overexpression
Shortens G1 and premature entry into S phase
Cyclin overexpression in tumours
Deregulates cell cycle
Cyclin dependent kinases (CDKs)
Catalytic subunits of cyclin/CDK complexes, have a common cyclin-binding domain
Cell ultrastructure includes nucleus, endoplasmic reticulum, mitochondria, Golgi network
Gene transcription
The process of copying the genetic information from DNA into RNA
Gene
A complex molecule associated with the chromosomes and acting as a unit or in various biochemically determined combinations in the transmission of specific hereditary characteristics
Genome
The entire complement of double stranded DNA within a cell
10% of DNA in mammals encodes the genome
Includes genes, repeating sequences, and "junk DNA"
3 billion base pairs in human genome
30,000 genes
Measure of gene expression
The appearance of a protein in a cell (expression)
The transfer of information housed within the genetic material to the machinery responsible for protein synthesis
Skeletal muscle is composed of elongated, multinucleate myocytes that contract upon electrical stimulation
The collective functionality of a set of proteins expressed in skeletal muscle cells does not mean those proteins are only expressed in those cells, as many are also expressed in many other cell types
Some proteins are unique to skeletal myocytes
DNA/RNA
Consists of adenine, thymine (uracil), cytosine, and guanine
Encodes an amino acid as a triplet of nucleotides (codon)
Start codon
AUG (methionine), initiates protein synthesis
Stop codons
UAA (ATT), UGA (ACT), UAG (ATC), cause protein chain to terminate protein synthesis
Eukaryotic gene transcription
Occurs in the nucleus
Synthesis of a single strand of RNA, a copy of the information stored in double stranded DNA
RNA synthesis is catalysed by RNA polymerase
Only one strand of DNA is used to make RNA
Types of RNA
Ribosomal RNA (rRNA)
Messenger RNA (mRNA)
Transfer RNA (tRNA)
mRNA
Carries information that encodes a protein sequence from DNA to the ribosome
Information stored as discrete "words" made of three nucleotides (codons)
Links the genome to protein synthesis machinery
Typical gene structure
Consists of the open reading frame (ORF) composed of introns and exons
ORF is contained between the start codon and stop codon
mRNA processing
1. Capped at the 5' end by 7-methylguanosine added by guanylyl transferase to protect against nuclease enzymes and enable CAP directed translation
2. Poly A tail added to the 3' end by poly (A) polymerase to prevent RNA degradation
RNA splicing
1. Removal of introns and ligation of exons by small nuclear ribonucleoproteins (snRNPs) and the spliceosome
2. Not an exact process
DNA/gene contains introns and exons, and the mRNA transcript is made up of introns and exons
The primary pre-RNA transcript undergoes mRNA processing and RNA splicing
Types of ligands
acetylcholine
adrenaline
insulin
growth hormone
acetylcholine ligand
adrenaline ligand
insulin ligand
growth hormone ligand
G-protein coupled receptor (GPCR)
Heterotrimeric G-protein composed of α, β & γ subunits that are connected to intracellular transduction system through a G-protein
GTP bound α subunit dissociates from β/γ subunits and interacts with secondary messenger system when ligand binds to receptor
Aderylate cyclase (second messenger system)
Communicating the interaction between a ligand and it's receptor to produce a cellular effect
Drug binds to receptor and activates G protein system to stimulate/inhibit effector system
If stimulated, effector system produces second messenger (cAMP)
Second messenger activates enzyme that changes the target protein
Progression through cell cycle:
Cyclin D/CDK4,6 control Rb phosphorylation
Cyclin E CDK2 controls Gl to S transition
Cyclin A/CDK2 controls S phase progression
Cyclin B/CDK1 controls G2 to M transition
Progression through G1:
Regulated by CDK4, CDK6 and CDK2
CDK4 in complex with cyclin D controls phosphorylation of Rb family of proteins
Further phosphorylation of Rb protein is mediated by CDK6 + cyclin D complex and finally by CDK2 + cyclin E complex
Transit of cells from G1 into S phase:
Regulated by CDK2 + cyclin E complex
Activity of CDK2 + cyclin E complex is needed for the duplication of centrosomes
Progression through S phase:
Regulated by CDK2 + cyclin A complex
CDK2 + cyclin A phosphorylates many proteins needed for transcription, DNA replication and repair
Also phosphorylates proteins needed to complete S phase and entry of cells into G2 phase
Progression through G2:
Cyclin A is degraded as cyclin B is actively synthesised
ProgressionG2 -> M phase transition:
Regulated by CDK1 + cyclin B complex
CDK1 + cyclin B complexes form during mid-to-late G2
Involved in centrosomes during prophase, causes centrosome separation, and is involved in chromosome condensation
Gene transcription
The process of copying the genetic information from DNA into RNA
Gene
A complex molecule associated with the chromosomes and acting as a unit or in various biochemically determined combinations in the transmission of specific hereditary characteristics