Biochem: Cellular and molecular biology Flashcards
What 2 types of cells exist and what are they?
Prokaryotic cells - no nucleus, such as bacteria
Eukaryotic cells - complex structure including nucleus
Where is a cells ribosomal RNA synthesised?
Nucleolus within the nucleus of a cell.
What is the difference between rough and smooth endoplasmic reticulum?
Rough endoplasmic reticulum has ribosomes attached to its outer surface.
What is synthesised at the smooth endoplasmic reticulum?
Fatty acids and phopholipids
Which cells is smooth endoplasmic reticulum abundant? What is its function?
Liver cells
Modify and detoxify molecules such as pesticides and carcinogens.
What is synthesised at the rough endoplasmic reticulum? Which cells are they abdudnant in?
Proteins, either for cell function (organelle or membrane proteins) or secretory proteins.
Cells that secrete large amount of proteins such as plasma cells secreting antibodies or pancreatic acinar cells secreting digestive enzymes.
What happens to secretory proteins after synthesis at the rough endoplasmic reticulum?
Secretory proteins transported in vesicles and transported to golgi complex.
They are modified at golgi complex then transport in second set of vesicles.
How is mitochondrial DNA inherited?
Maternal
How do lysosomes function.
Lysosomes contain destructive enzymes within a single membrane (pH4.8). Materials brought in by endocytosis or phagocytosis.
How do peroxisomes function
Contain oxidases that oxidase organic substances which generate toxic hydrogen peroxide.
Main organelle for oxidising fatty acids.
What is endocrine signalling?
Release of hormones from endocrine glands, the hormones are then carried in the bloodstream to a distant target site.
What is paracrine signalling?
Signalling molecule produced by a cell acts only on cells very close to it. Neurotransmitters work by paracrine signalling.
What are the 4 types of cell signalling?
Endocrine
Paracrine
Autocrine
Cell signalling via membrane attached protein
Where are eicosanoids made? What are they composed of?
Plasma membrane of all mammalian tissue
20-Carbon fatty acid chains (arachidonic acid)
What are the 4 types of eicosanoids?
Prostaglandins
Prostacyclins
Thromboxanes
Leucotrienes
Prostaglandins, Prostacyclins, Thromboxanes (collectively known as prostanoids) are catalysed by which enzyme?
Cyclooxygenase (COX)
Where are COX 1 and COX 2 expressed?
COX 1 is found in tissues that produce prostaglandins constantly such as stomach mucosa
COX 2 is only expressed at sites of inflammation so is inducible
How do NSAIDs work
Block the first oxidation step of arachidonai acid that is catalysed by COX, newer NSAIDs or more selective for COX-2 (competitive inhibitor)
How does aspirin work
Inhibits both COX-1 and COX-2, permanently acetylating the active site. At low doses it can inhibit thromboxane synthesis, used in the management of PET.
How does nitrous oxide enter a cell?
So small passes straight into the cell
What are the 3 forms of NO synthase that produced NO?
Endothelial NO Synthase
Induciable NO synthase
Brain NO Synthase
Endothelial cells on blood vessels release NO in response to what?
What does the release of NO cause?
Shear stress, agents such as acetylcholine
Diffuses into underlying smooth muscle, reacts with iron to produce cGMP, causing muscle relaxation
Related to this why does BP in pregnancy fall?
Vasodilation mediated to an increase in NO.
What is the expression of iNOS induced by?
Inflammatory signals from bacterial cell wall products, activated macrophages and neutrophils.
NO helps to kill invading microorganisms
Describe the concentrations of calcium within cells and why this is important in cell signalling?
Cells maintain low intracellular concentrations of calcium compared to extraceullar or within the endoplasmic reticulum. Extracellular signals open Ca channels, increasing the conc of intracellular calcium and active calcium responsive proteins in the cell.
What is the purpose of oxidative phosphorylation and where does it occur?
Produce ATP
In mitochondria
What is cAMP (cyclic adenosine monophosphate) synthesis from?
By which enzyme is it synthesised & where?
What is it destroyed by?
ATP
Adenylate Cyclase bound in the plasma membrane
cAMP phosphodiesterase
How does cAMP change the activity of different enzymes?
Phosphorylation
Dephosphorylation mediated by cAMP depended protein kinases.
Cellular response to cAMP changes depending on the cell type. What is its affect in ovarian cells?
Formation of estradiol and progesterone
How does sildenafil work?
Enhances vasodilatory effects of cGMP by inhibiting phosphodiesterase 5 (which breaks down cGMP
What are the main 4 classes of cell-surface receptors?
G-protein-coupled-receptors
Ion channel receptors
Tyrosine-kinase-linked receptors
Receptors with intrinsic enzyme activity
How do Gs protein and protein Gi affect adenylate cyclase.
Gs activate it.
Gi inhibit it.
What enzyme does Gq activate?
Phospholipase C, which in turns triggers the productions of a second messenger such as IP3 or diacylglycerol
What is the affect of a ligand binding to a tyrosine kinase linked receptor
The ligand binding results in the formation of a receptor from 2 monomeric receptors. The end in the cytoplasm then activates tyrosine kinase which then phosporylates tyrosine residues.
Name major classes of cell adhesion molecules (enable cells to adhere to each other and to the extracellular matrix)
Cadherins
Immunglobulins
Selectins
Integrins
What ligand does selectin bind to?
Carbohydrate residues on the cell surface (relatively weak)
What are the 4 major classes of cell junctions?
Adhering junctions
- Tight junctions,
- Adheres junctions + desmosomes
- Hemidesmosomes,
Communicating junctions
4. Gap junctions.
How do gap junctions function
Mirrored protein units located in plasma membrane, allow passage of small signalling molecules, Ca2+ and cAMP but not large molecules such as proteins. Important within myometrium in labour.
In the cell cycle when is DNA duplicated?
S phase (synthesis phase)
At which stage is the genome halved?
Mitosis
What occurs in prophase of mitosis
Chromsomes condense
What occurs in metaphase of mitosis
Sister chromatids produced by DNA replicated during the s phase become aligned in the centre of the cell
What occurs in anaphase of mitosis
sister chromatids separate and move to opposite poles along mitotic spindles
What occurs in telophase of mitosis
nuclear envelope break downs and reforms around the segregated chromosomes.
What occurs in cytokinesis of mitosis
Final physical breakdown of the cytoplasm to yield 2 daughter cells
At which stage does G1 and G2 occur allowing for cell growth and monitoring
G1 between Mitosis and Synthesis
G2 between S and M
At which stages are DNA damage checkpoints.
What happens if damage is detected
Before/after S phase
Cyclin-depedant kinase 2 (CDK2) is inhibited & progression through the cell cycle is stopped.
If DNA damage is not reparable the cell undergoes DNA apoptosis
Carciomas are serviced from…
endoderm and ectoderm
Sarcomas are derived from…
Mesoderm Leukemias are a class of sarcoma
What type of proteins involved in normal cell growth that can lead to cancer is mutated?
Growth factors (or their receptor/signal trsdunction protein/transciption factors) - usually dominant
Cycle cycle proteins - tend to be recessive (e.g. p53)
Virus encoated proteins
Describe how HPV uses oncogenes to establish benign tumours of epilthial cells (warts).
HPV enters epiethial cells by abrasion, the viral DNA is transported to the cell DNA where it transcripts to oncogenes E6/E7 which suppresses tumour suppressor genes (p53 & pRb) leading to differentiation.
What is the benefit of blocking VEGF in the treatment of cancer?
Tumours growing large than 2mm need there own bloods supply (angiogenesis), growth factors such as VEGF stimulate angiogenesis.
What are the 3 types of RNA
Messenger RNA (carries message from DNA to specify correct order of amino acids during protein synthesis) Transfer RNA (Interprets mRNA, each amino acid has its own tRNA) Ribosomal RNA
What makes up a nucleotide
Nitrogen containing base (purine and pyrimidine)
5 carbon sugar (pentose)
Phosphate group
What re the 4 bases in DNA? How do they differ in RNA?
Purine: Adenine Guanine
Pyramidine: Thymine and cytosine
RNA: Uracil replaces thymine
How does the pentose sugar differ between DNA and RNA
DNA: Deoxyribose
RNA Ribose
In DNA’s double helix which base also bind to
i) Adenine
ii) Cytosine
Adenine and thymine = 2 weak hydrogen bonds
Cytosine and Guanine = 3 week hydrogen bonds
Summarise DNA synthesis
Helicases break the hydrogen bonds, leading and lagging strand of DNA. Leading strand DNA polymerase continuously adds completentary nucleotides. Lagging strand add in segments (okazaki fragments) added together by DNA ligase.
Summarise RNA synthesis
RNA polymerase binds to promotor region, transcripts in 5-3prime direction. Uracil replaces thymine. Only 1 strand copied.
What is splicing
After transcription to mRNA, non-coding introns are removed, leaving only introns. Includes alternative slicing (removes some introns, so different mRNA variants from same gene)
What is a codon?
Within mRNA, triplet of nucleotides which code for an amino acid. Many different codons may specify the same amino acid.
Describe protein synthesis (translation) & where does it occur
Multiple ribosomes move along mRNA, tRNA deciphers code - correct tRNA for specific codon attaches with amino acid on following side. Forms chain of amino acids.
What are the 2 geometric arrangements of secondary structure of proteins
Alpha helix
Beta sheet
stabilised by hydrogen bonds
Then folded into tertiary structure, then formed into quaternary sub units.
What does each of the following test for?
Southern blotting
Northern blotting
Western blotting
Southern blotting - DNA
Northern blotting - RNA
Western blotting - Proteins
What does polymerase chain reaction achieve
Significantly increases the amount of DNA or RNA
What is post translational modification?
After translation of a protein, the quaternary structure can be further edited with add-on of acetyl group, phosphate group or carbohydrate group.
