module 2 Flashcards
chracterisitcs of the genetic code
Degenerate: many codons can code for the same amino acid
Stop codons terminate protein synthesis
Start codon also codes for methionine
outline the steps of transcription
- Initiation:
Sigma factors on RNA polymerase binds onto the promoter sequence located upstream of the initiation site
RNA begins to unwind the double helix - Elongation
-Sigma factor releases
Moving along in a 5’ to 3’ direction, RNA polymerase synthesises a new strand using complementary free floating nucleotides whilst unwinding it - Termination
At the termination site, RNA polymerase and the mRNA strand are released
Outline steps of translation
Translation step 1: Initiation
Recognition site on mRNA binds to small subunit
methionine -charged tRNA binds to AUG start codon
Large subunit joins initiation complex
Translation step 2: elongation
Codon recognition: anitcodon of incoming tRNA binds to codon at A site
Peptide bond formation:
Elongation: free tRNA moves to E site and is then released as the ribosomes shifts by one codon
Repeats
Translation step 3: termination
Release factor binds to complex when stop condon enters A site
Causes the release of polypeptide from the tRNA in the P site
Remain components separate (mRNA and ribosomial subunits)
Pre-translation
Pre-mRNA matures to mRNA in the nucleus, involving 5’-capping, poly-A tail, intron splicing
mRNA migrates to cytoplasm for translation to polypeptide
Signal sequences determine where protein is targeted (cytoplasm, rough endoplasmic reticulum, organelles)
Different types if energy in biological systems
- Electrical – separation of charges
Electrical gradients across cell membranes help drive the movement of ions - Chemical – stored in chemical bonds
Energy stored in covalent bonds released during hydrolysis of organic molecules - Light – electromagnetic radiation stored as photons
Light energy is captured by pigments in the eye or in plant photosynthesis - Mechanical – energy of motion
Mechanical energy is produced in muscle movements - Heat – transfer due to temperature difference
Heat can be released in biochemical reactions and alter body temperature
Metabolism
sum total of all the chemical reactions occurring in a biological system at a given time
Metabolic reactions involve energy changes.
What is free energy and how does it relate to exergonic and endogonic reactions
Gibb’s Free Energy (G) = amount of energy available to do work
∆Greaction = Gproducts – Greactants
∆G < 0 — free energy is released in the reaction = exergonic
∆G > 0 — free energy is required for the reaction = endergonic
describe catabolic and anabolic reaction
Catabolic reactions break down larger, more complex molecules into smaller ones and often release energy
Anabolic reactions link smaller molecules to form larger, more complex molecules and require an input of energy.
Activation energy
Catalysts: increase rate of chemical reactions
Active site and substrate reaction
Reduce activation energy
Easier path
Does not change free energy
Affect orientation of substrate , physical strain/conformational changes
How does ATP store energy
Potential chemical energy stored in the bonds between phosphate groups
Negative charge of phosphate group would repel each other
separation (hydrolysis) is spontaneous reactions, releasing free energy and adp (exergonic)
phosporalation of ADP forms ATP (endergonic)
Redox reactions and role of electron carriers in the cell
more reduced = more free energy
photosynthesis
Co2 + H2O —> O2 + C5H12O6
Steps of the light reaction stage
- Light energy in the form of photons is absorbed chlorophyll molecules in photosystem 2 causing it to go into an excited state
- Energy is passed to chlorophyll molecules in the reaction centre which then donates the electron to a primary electron acceptor
- Having lost an electron, chlorophyll molecules receive electrons from the dissociation of hydrogen ions and oxygen of water
- Excited electrons pass through a series of proteins in the membrane (Plastoquinone, cytochrome, plastocyanin) which causes it to gradually lose energy as it is being used to pump hydrogen ions across the membrane into the stroma/thylakoid lumen which creates a proton gradient
- Electrons move to photosystem 1 and passes to chlorophyll inside reaction centre
- Photons from light excite electrons allowing it to transfer to the electron acceptor, forming high energy electron
- Electrons pass through NADP reductase and in the process reduced NADP+ to NADPH
- Accumulation of hydrogen protons in the thylakoid lumen forms a proton gradient which allows ATP synthase to generate ATP from ADP
Carbon fixation - light independent
Microbiomes
The different microorganisms in an organism
example
What is the holobiont concept
Holobiont: symbiotic ecological unit usually between a host and microbiota
outlines how our symbiotic relationship is impacted by the environment
importance of a fibre-rich diet
microbiome in the colon converts fibre into short fatty acid chains via microbial fermentaion
Mucus layer of colon is eroded causing barrier dysfunction as they cannot form a proper structural arrangement with the host’s gut
Results in breaking down the interface of the colon causing disease.
List the 4 different chemical signals and their affect
- Autocrine signals affect the cells that made them - bind to receptors that made them
- Juxtacrine signal affect only adjacent cells - binds to adjacent cells
3, Paracrine signals affect nearby cells - Circircalitng signals: (horomones) are transported by the circulatory systems and bind to receptors in distant cells
Requirements to respond to a signal
A cell must have a specific receptor to detect signal
A signal transduction pathway is the sequence of event that lead to the response
Responses may involve enzymes and transcription factors that are either activated or inactivated to have the desired response
Process of a signal transduction pathway
- Signal arrives at a target cell
- The signal molecule binds to a receptor protein in the cell surface or inside the cytoplasm
- Signal binding initiates the conformational change of the receptor and exposes the active site
- Activated receptor activates a signal transduction pathway which induced cellular changes
2 types of receptors based on its location
Intracellular receptors:
inside the cell interacting with physical or chemical signals
Usually respond to non polar signals as it can diffuse directly across the lipid bilayer of the cell membrane to encounter its receptor in the cytoplasm or nucleus
Membrane receptors:
large or polar ligand bind to cell membrane receptors
Respond to polar signals flowing outside the cells and cannot diffuse through the cell membrane and is embedded in the membrane
3 types of receptors based on their mechanisms
Ion channel receptors: allows ions to enter or leave the cell
Acetylcholine binds to 2 of the 5 AChR subunits causing the channel to chage shape and open
Channel is lined with negatively charged amino acids, allowing Na+ to flow intot he cell
NA+ buildup in cells initiates events that lead to muscle contraction
Protein kinase receptors: phosphorylate themselves
Insulin binds to a subunits of the insulin receptor
Conformation change in the b subunit occurs, transmitting a signal to the cytoplasm that the insulin is present
Signal activates the receptor’s protein kinase domain in the cytoplasm
Phosphorylates insulin-response substrates, triggering a cascade of chemical response inside the cell
G protein-coupled receptors: work via an intermediary
Hormone binding to receptor activates the G protein - GTP replaces GDP
Activated g protein subunit activates effector protein that causes changes in cell function
What can a cell do in response to a signal
Open an ion channel
Change enzyme activity
Differential gene expression
How do adjacent cells in animal and plant cells communicate
Plant cells
Through plasmodesmata
Plasmodesmata: reasonably large membrane lined channel through which molecules can pass
Animals cells
Gap junctions form a narrow channel through which ions can pass
