| Quorum sensing - Detection of an autoinducer | Detects production of eg. toxin or signal molecules. The greater the cell density, the more abundant the signal. There is a threshold in which cells have to respond. |
| Quorum sensing and virulence in Staphylococcus aureus | Arg is a two component regulatory system based around an operon with 2 promoters. Constitutively expresses AgrA (Response protein, activates P3 producing RNAIII), B (transmembrane protein, secretes mature AIP), C (AIP receptor, binds AIP then phosphorylates AgrA) and D (Autoinducing peptide (AIP)). At low cell density concentration of AIP is low
AgrC inactive so no phosphorylation of AgrA to activate P3 and produce RNAIII. |
| What are biofilms? | Structured clusters of cells, enclosed in a self-produced polymer matrix and attached to a surface:
Cells and tissues solid surfaces. Estimated that 80% all microbial biomass is in biofilms. Enable pathogens survival in the environment and in hosts |
| RNA III | Regulatory rna for many genes. Represses adhesion. Induces elements to drive invasion. Encodes mrna to hld, forms secondary and tertiary structure. 14 hairpin bends and a globular shape bring 3 to 5 ends close. Binds to hlaAmRNA at the shine-delgano region. |
| Common characteristics of biofilms | Cells enclosed in polymer matrix of exopolysaccharides, proteins and nucleic acid. Formation initiated by extracellular signals present in the environment. Biofilm protects bacteria against the host immune response, desiccation and biocides. |
| How do biofilms form? Five stages | 1. Initial attachment – flagella, type I pili
2. Irreversible attachment – LPS, Type IV pili
3. Maturation I – mirocolonies, produce aliginate, repress flagella
4. Maturation II – Quorum sensing
5. Dispersion – release planktonic cells |
| Sequence content | As genome gets larger 14MB to 3.2GB, the non-coding region increases proportionally. Gene-dense regions (1 in 20kb), gene-poor regions (1 in 200kb). |
| Composition of Human Genome | Transposons, LINEs, SINEs, Introns, non-rep. DNA. |
| Function of Chromatin | Package DNA, Regulate gene expression, Prevent DNA from being damaged, regulate gene expression, Reinforce macromolecule structure for mitosis |
| DNA Packaging | Heterochromatin has condensed chromatin structure and is inactive for transcription.
Euchromatin has loose chromatin structure and active for transcription.
Chromosomes interact with the nuclear lamina and occupy specific areas of the nucleus. |
| Histones and their assembly | Small (10 – 13kD), basic and highly conserved. Form a solenoid (supercoiled) structure with DNA wound around core of histone protein. Nucleosome contains twomolecules of H2A, H2B, H3 and
H4, plus one of H1. Assembly: The “handshake” interaction between H3-H4 tetramer and 2x H2A-H2B dimers. Histones are modified at their “tails”: Acetylated, Methylated, Phosphorylated or Ubiquitylated. |
| Steps at which eukaryotic transcription can be controlled | Histone modification Acetylation, methylation. Transcriptional control, RNA polymerase, Transcription factors. RNA processing control, RNA transport and Localisation control. |
| Origins of replication | 1. ORC detects the origin.
2. Binds and recruits Cdc6 and Cdt1 Steps 1-3 are G1 phase
3. They recruit Mcm helicase
4. Cdc6 gets phosphorylated and degraded. Steps 4-6 are S Phase
5. Phosphorylation of ORC
6. DNA replication
7. Normal with duplication Step 7 is G2,M phase |
| Organisation of human centromere | Fundamental importance in chromosome partitioning, site of kinetochore assembly. Contain nucleosomes with variant histone protein. Assembled on long regions of highly repetitive DNA. Structures: Cohesin, links the two sisters together, microtubules, kinetochore plates, chromatin with H3 but de-methylated at lysine 4, chromatin with H3 histone. |
| Telomere sequences are repetitive | Vary in size and repeat number. Vertebrate sequence is TTAGGG, repeated over several kb
Yeast telomeres are several hundred bps. |
