Section 1 Cells Flashcards
Define SNPs
Single nucleotide polymporphisms
A form of DNA variation
Always biallelic
What portion of SNPs occurs in the coding regions?
1%
What is linkage disequilibrium in the context of SNPs?
Neutral SNPs are coinherited with a disease-associated polymorphism as a result of proximity
Is the effect of SNPs on disease susceptibility weak or strong?
Weak
Define CNVs
Copy number variations
Form of DNA variation consisting of large contiguous stretches of DNA
What portion of CNVs is in the coding regions?
50%
Do CNVs underlie a large portion of phenotypic diversity?
Likely, 50% of CNVs are in coding regions
Define histones
Central core structure of highly conserved low molecular weight proteins around which DNA wraps to form nucleosomes
Define nucleosomes
DNA segments wrapped around histones
How long are DNA segments in a nucleosome?
147bp
How does chromatic structure regulate gene activity?
Densely packed heterochromatic is not available for transcription
Dispersed euchromatic is available for transcription
What is the effect of histone methylation?
Methylation of histone lysine residues can lead to transcription activation of repression, depending on which histone residue is marked
What part of histones can be methylated?
Lysines and arginines
What is the effect of histone acetylation?
Increased transcription
How does histone acetylation occur?
Histone acetyltransferases (HATs) acetylate lysine residues, which opens chromatin
What is the effect of histone deacetylases (HDACs)?
Reversal of histone acetylation
What is the effect of histone phosphorylation?
DNA may be opened for transcription or condensed depending on which serine residue is phosphorylated
What part of histones gets phosphorylates?
Setine residues
What is the effect of DNA methylation?
Typically transcriptional silencing
What is the role of chromatic organising factors?
Bind to non-coding regions and control long-range looping of DNA, regulating the spacial relationships between enhancers and promoters.
What is the structure of histones?
Octamers of histone proteins, the subunits are positively charged
Are microRNA and lncRNA transcribed or translated?
Transcribed by not translated
What is the role of microRNA?
Post-transcriptional silencing of gene expression
Does each microRNA regulate one or multiple protein-coding genes?
Multiple
How is microRNA produced?
miRNA genes are first transcribed into a primary transcript. The pri-miRNA is then processed into progressively smaller segments, for example, trimmed by Dicer
How does miRNA work?
miRNA is associated with RISC. When miRNA binds to target mRNA, RISC either induced mRNA cleavage or represses translation to post-transcriptionally silence mRNA.
What is the overall effect of miRNA, Dicer and RISK on gene expression?
Post-transcriptional gene silencing
What is the role of lncRNA?
Modulation via a variety of mechanisms
Give an example of how lncRNA modulates gene expression
Bind to chromatin to restrict RMA polymerase reaching coding genes
Help ribosone binds and gene activation
Promote chromatic modification
Assemble protein complexes to alter chromatin structure
What is XIST?
As example of lncRNA that silences the X chromosone in females.
List three different sites of molecule breakdown within the cell
Proteasome, lysosome and peroxizome
What is the function of a proteasome?
Breakdown of denatured or tagged cytosolic proteins
Give an example of proteasome function
Proteases in antigen presenting cells produce peptides displayed on MHC molecules
What is the function of a lysosome?
Contain degrading enzymes for digestion of a wide range of molecules (proteins, polysaccharides, lipids, nucleic acids)
Intracellular organelle breakdown (autophagy)
Killing and catalysis of phagocytosed microbes
What is the function of peroxisomes?
Contain catalase, peroxidase, oxidative enzymes
Breakdown of very long-chain fatty acis
Generating hydrogen peroxide
Which cellular structure allows movements of structures within the cell and the cell itself?
Cytoskeleton
What is the cytoskeleton made up of?
Actin (microfilaments)
Keratin (intermediate filaments)
Microtubules
On which surface of the plasma membrane is phosphatidylinositol located?
Both
On which surface of the plasma membrane is phosphatidylserine located?
Inner surface
Can be flipped to outer surface to become an “eat me” signal
On which surface of the plasma membrane are glycolipids and sphignomyelin located?
Extracellular
How can components of the membrane be confined to discrete domains?
Localisation to lipid rafts or intercellular protein-protein interactions (e.g. tight-junctions)
What is a common function of actin filaments?
With actin nucleating, binding and regulatory proteins, control cell shape and movement
Muscle contraction
What is a common function of intermediate filaments?
Tensile strength
What is a clinical application of intermediate filaments?
Have tissue-specific patterns of expression (useful for cancer indentification)
What is a common function of microtubules?
Lines for molecular motor proteins (kinesins and dyneins) to move components
Sister chromatid separation in mitosis
Form the core of primary cilia, motile cilia (bronchial epithelium), or flagella (sperm)
List the three basic types of cell-cell junctions
Tight/occluding junctions
Anchoring junctions (adherins junctions and desmosomes)
Communicating junctions
What is the clinical significance of Adherins junctions (type of anchoring junctions)?
Loss of E-canherin explains the discohesive invasion pattern of some gastric cancers and breast carcinomas
Which cells have higher concentrations of SER or in which cells SER have an important function?
Cells that synthesise steroid hormones (gonads, adrenals), catabolise lipid-soluble molecules (hepatocytes) or store calcium (sarcoplasmic reticulum in muscle cells)
What are the functions of mitochondria?
ATP generation
Intermediate metabolism
Regulation of apoptosis
List the four types of cell signalling
Paracrine
Autocrine
Synaptic
Endocrine
How can endothelial cells regulate regulate vasomotor tone?
NO produced by endothelial cells diffuses into smooth muscle cells to reach an intracellular receptor.
Activates cGMP, which causes smooth muscle relaxation.
