Questions Flashcards
What are the three foundations of biology?
Evolution through natural selection, unity of biochemical processes, and cell biology.
What features are unique to prokaryotes?
Always microscopic Always unicellular No nucleus One circular chromosome Bacteria have no histones Bacteria have a peptidoglycan cell wall Smaller Ribosomes
What features are unique to eukaryotes?
A division of labour in the cytoplasm
Nucleus and histones on DNA
An endomembrane system
A cytoskeleton
What are the major functions of intracellular membranes?
Provide a surface for biochemical reactions
Establish a number of compartments to prevent mixing
Provide transport of materials within cell or out of cell
What are the major elements of the cytoskeleton and their functions?
- Actin filaments interact with myosin motors. They contribute to muscle contractions and cytoplasmic streaming
- Microtubules interact with kinesin or dynein motors. Can form protofilaments that form flagellum (moved by dynein) or transport system for kinesin to carry molecules.
- Intermediate filaments are predominantly static
What are the various ways molecules can cross membranes?
- Diffusion
- Osmosis - special case of diffusion, facilitated by aquaporins
- facilitated diffusion is diffusion facilitated by transport proteins (carrier or channel)
- Active transport (often coupled transport)
- Phagocytosis/Pinocytosis
What are some of the ways an enzyme can reduce the EA of a reaction?
- Enzyme can help substrate reach activation energy
- Enzyme brings pieces together in the right orientation
- Enzyme strains the substrate
- Enzyme adds charges to substrate
What is the role of ATP in energy harvesting/expending reactions
Energy released from an exergonic used to phosphorylate ADP to ATP, which is then dephosphorylated to drive an endergonic reaction.
What are the key differences between cellular respiration and fermentation?
Cellular Respiration: - complete oxidation - aerobic - waste products: water and CO2 - Net energy trapped: 32 ATP Fermentation: - Incomplete oxidation - Anaerobic - waste products: organic compound and CO2 - Net energy trapped: 2 ATP
What are the overall products of Aerobic Respiration?
Each Glucose yields 6 CO2, 10 NADH + H+, 2 FADH, 4 ATP
What is the function of the Electron Transport Chain?
Electrons given up from reduced NADH are passed along the chain and used to reduce Oxygen, which then reacts with 2 H+ to form water. The proteins of the chain take some energy from the spin of the electron to pump protons from the mitochondrial matrix to the inner membrane space and create an electrical gradient. This gradient is harvested by ATP synthase which allows the protons back through and uses that energy to phosphorylate ATP
What is the structure of ATP synthase?
ATP synthase is partially in and out of the inner mitochondrial membrane and has a rotating shaft. The protons cause the shaft to rotate while diffusing down, this powers the ‘forge’
ADP comes in with a phosphate and is given a whack, which initiates a covalent bond and creates ATP
What is the evidence for the theory of endosymbiosis with mitochondria and chloroplasts?
- appear morphologically similar to bacteria
- surrounded by an outer membrane similar to the cell membrane while inner membrane invaginates to form lamellae or cristae. Derive from Gram negative bacteria
- semi autonomous, own genome (circular chromosome and small ribosomes)
- own machinery for synthesising proteins
- metabolism like existing prokaryotic organisms (cyanobacteria and purple bacteria)
- some chloroplasts still have a peptidoglycan cell wall between membranes
What happens during interphase?
G1: each chromosome is a single, unreplicated DNA molecule with associated proteins. To move to the next stage, a checkpoint must be passed (DNA damage)
S: DNA replication. Each chromosome is duplicated to become two sister chromatids that remain joined until meiosis. The cell checks for incomplete replication or DNA damage
G2: The cell makes preparations for mitosis, such as synthesising and assembling structures. Checkpoint for DNA damage.
What happens during Prophase?
The chromosome continues to coil and super coil, making it more and more compact and condensing into visible chromosomes. The chromosomes consist of identical, paired sister chromatids formed in S phase. The centrosomes start to develop the spindle and move to opposite poles.
What happens during Prometaphase?
The nuclear envelope breaks down. Kinetechore microtubules appear and connect the kinetochores with the centromeres.
What happens during Metaphase?
The centromeres become aligned in a plane at the cells equator. The cell checks that all kinetochores are attached.
What happens during Anaphase?
The paired sister chromatids separate, and the new daughter chromosomes begin to move toward the poles.
What happens in Telophase?
The spindle breaks down, the separated chromosomes reach the poles, nucleoli and nuclear envelopes reform and the cell divides by cytokinesis.
How is cell division regulated?
Regulation and checkpoints rely on activity of cyclin-dependent kinases, which need to be activated by binding to a cyclin. Different combinations exist for various checkpoints, different cyclins are produced at different points in the cycle and can be inhibited if there is damage.
What is different in Meiosis to Mitosis?
Meiosis I - homologs pair and exchange genetic material, separation in anaphase I does not separate chromatids, only homologous pairs
Meiosis II - mostly like mitosis but with no DNA replication, results in 4 genetically distinct daughter cells.
Where might you find squamous cells?
Epithelial tissue cell type. Squamous cells are thin, and are typically found in layers (stratified). They are found in the skin.
Where might you find columnar cells?
Epithelial tissue cell type. Columnar cells are tightly packed and have tight junctions. They can have cilia and are often polarised. They are often found in tubules.
Where might you find cuboidal cells?
Epithelial tissue cell type. Cuboidal cells are tightly packed with tight junctions. These can also be found in tubules or in glands, or lining organs like the ovary.
What makes up cartilage?
Cartilage is rich in collagen and elastin, which makes cartilage firm and flexible.
What makes up bone?
Collagen fibres are hardened by calcium phosphate to provide a strong, rigid connective tissue.
What makes up adipose tissue?
Adipose cells form loose connective tissues that provides a barrier to heat loss.
What actions can the body take to reduce body temperature?
Evaporation, blood flow to skin, decreased metabolism.
What actions can the body take to increase body temperature?
Reduce blood flow to skin, increase metabolic rate.
What is the basic outline of a signal transduction pathway?
A signalling molecule binds to a receptor, causing a conformational change that may expose an active site. The receptor protein then conveys the message to the cell. This may be done by activating proteins or initiating a cascade of reactions. This will cause a response in the cell which could be short term (e.g. increase in enzyme activity), or long term (e.g. altered DNA transcription).
What determines the location of a signal’s receptor?
The ability of the signal molecule to cross the phospholipid membrane.
E.g. cortisol has an intracellular receptor as it is a steroid, and is thus lipid soluble.
Thyroxine and Oestrogen receptors are found in the nucleus.
Acetylcholine is not lipid soluble and so has a membrane bound receptor.
Explain the action of a Gated Ion Channel Receptor.
This is direct transduction.
Binding of a signal causes a conformational change in the receptor such that the channel in the protein is open and ions can enter.
E.g. Acetylcholine binds to Sodium channels and allows them to enter, which may lead to contraction or an action potential.
Explain the action of a Protein Kinase Receptor.
This is indirect transduction via a second messenger.
The alpha subunit binds the signal, which causes the beta-subunit to change shape. This in turn activates the receptor’s protein kinase domain in the cytoplasm, which phosphorylates the response substrate, leading to a cellular response.
E.g. Insulin receptors.
Explain the action of a G-Protein linked receptor.
When a signal binds to the receptor, a conformational change occurs which makes it possible for the G-protein to interact with the receptor, which phosphorylates GDP to GTP and activates the G-Protein. The G-protein subunit containing GTP is now able to move through the membrane and bind to an effector molecule, which initiates a cascade of reactions leading to a cellular response. The GTP is hydrolysed back to GDP.
E.g. Epinephrine binding to an epinephrine receptor leads to activation of Adenylyl Cyclase, which causes a cascade of reactions leading to increased glucose release and the prevention of glycogen production from glucose.
What are the characteristics of peptide/protein hormones?
Major group of hormones
Water soluble so are easily transported in the blood.
Not membrane soluble - receptors in membrane.
Packaged within vesicles in cells and secreted by exocytosis.
E.g. insulin.
What are the characteristics of steroid hormones?
Synthesised from steroid cholesterol
Lipid soluble so can pass through cell-membranes - internal receptors.
Diffuse out of cells and are bound to carrier molecules in the blood.
E.g. testosterone.
What are the characteristics of Amine proteins?
Mostly synthesised from tyrosine
can be water or lipid soluble so mode of action differs
E.g. Epinephrine, Thyroxine.
What hormones are secreted by the Anterior Pituitary and what do they do?
- Thyrotropin Stimulating Hormone (TSH) - targets thyroid gland and causes Thyroxine release.
- ACTH - targets adrenal gland and causes Cortisol release
- Follicle Stimulating Hormone (FSH) - stimulates oocyte maturation and release in ovary, supports function of sertoli cells in the testis
- Growth Hormone (GH) - stimulates protein synthesis and growth in most cells, stimulates milk production in breast cells.
What hormones are secreted by the Posterior Pituitary and what do they do?
Releases Neurohormones that are secreted into blood by neurons that originate in the hypothalamus Oxytocin - stimulates contractions in uterus. Antidiuretic Hormone (ADH) - regulates water uptake in kidneys.
What is the structure and function of the Adrenal Gland?
Has an outer cortex and an inner medulla.
The outer cortex secretes cortisol and aldosterone.
The inner medulla secretes epinephrine and norepinephrine.
What is the Fight or Flight Response?
Release of Epinephrine and Norepinephrine in response to stressful situations. Rapid release as the adrenal medulla is controlled by the nervous system.
Targets the circulatory system, muscles, liver and fat cells.
Causes heart to beat faster, blood pressure increase, blood flow diverted to muscles, liver cells break down glycogen and secrete glucose, fat cells release fatty acids.
How does hormone release in the Anterior pituitary work?
Controlled by the hypothalamus.
Neurohormones in the hypothalamus have terminals on blood vessels in the stalk, these neurons secrete releasing neurohormones that travel via the portal blood vessels to the anterior pituitary where they act on cells to stimulate the release of hormones into the blood. Thus the anterior pituitary is an endocrine gland.
How are hormones from the pituitary regulated?
The External or Internal signal can stimulate or inhibit the hypothalamus.
Hypothalamic neurons secrete releasing hormones that stimulate anterior pituitary cells to release tropic hormones. These tropic hormones inhibit the hypothalamus, but also stimulate an endocrine gland to produce a hormone.
This hormone causes a cell response, but also negatively feeds back to they hypothalamus and to the pituitary.
What is thyroxine?
A lipid soluble hormone secreted by the thyroid that binds to nuclear receptors in most body cells and activates transcription of enzymes involved in metabolic pathways. This causes an increase in metabolic rate, often in response to temperature changes.
Thyroxine is crucial for development and growth.
How is thyroxine synthesised and secreted?
- A follicle cell in the thyroid takes up iodine from the blood.
- The cell synthesises thyroglobulin from tyrosine.
- Thyroglobulin is secreted into the follicle lumen and iodinated.
- Iodinated thyroglobulin is taken up by the follicle cell by endocytosis.
- Lysozymes break up thyroglobulin into T3 and T4
- T3 and T4 are secreted into the blood.
This process is stimulated by Thyroid Stimulating Hormone (TSH), which is regulated in the same was as other anterior pituitary tropic hormones via negative feedback.
What is hyperthyroidism?
A disease of the thyroid gland characterised by very high levels of thyroxine. Autoimmune (Grave’s Disease), an antibody binds to the TSH receptor in follicle cells of thyroid, causing high levels of Thyroxine, but low levels of TSH - negative feedback ineffectual.
Symptoms: High MR, feeling hot, enlarged thyroid gland, weight loss.
What is hypothyroidism?
A disease of the thyroid gland characterised by very low levels of Thyroxine.
Can be autoimmune (Hashimoto’s Disease) or be caused by low dietary iodine, meaning the follicle cells fail to make thyroxine.
No negative feedback of TSH, so thyroid continues to make thyroglobulin, but poorly iodinated.
Symptoms: enlarged thyroid, low cell metabolism, intolerance to cold, physical and mental lethargy.
What is the autonomic nervous system?
An important part of the peripheral nervous system controlling involuntary activity.
Parasympathetic = rest and digest
Sympathetic = Fight or flight
How are action potentials communicated between cells?
When the action potential is received by the axon terminal, it stimulates the influx of Ca2+, which stimulates the release of vesicles filled with neurotransmitters into the synaptic cleft by endocytosis.
These neurotransmitters bind to receptors on the postsynaptic cell and initiate a response
What is the Limbic System?
Portion of the central nervous system responsible for instincts, long term memory formation and physiological drives such as hunger, thirst, pleasure and pain.
Amygdala: fear and fear memory
Hippocampus: transfers short term memories to long term memories.
What parts of the brain are responsible for language?
Language abilities usually localised to the left hemisphere.
Broca’s area (Frontal lobe) is essential for speech, movements required to produce speech.
- damage will result in loss of ability to produce language, broken speech, but patient is aware and can understand language
Wernicke’s are (Parietal and Temporal Lobe) is essential for understanding speech and use of correct words, more sensory than motor aspects, commands to speak formed here
- damage will result in inability to understand language, can’t choose the right words or express thoughts, patient is not aware, can speak clearly but doesn’t make sense.
Normal language depends on the flow of information among various areas of the brain.
In what ways does sleep help learning and memory?
Helps you to focus well during waking hours and forms neural connections to store newly acquired information while you sleep.
What is the typical timeline of an immune response?
0-4 hours: infection recognised by phagocytes and soluble components of the innate immune system, reliance on barriers (1st line)
4-96 hours: Recruitment of effector cells of the innate response (induced response, 2nd line)
96+ hours: Transport of antigen to lymphoid organs for recognition by T and B cells and proliferation of these cells (3rd line)
Removal of infectious agent
What are the characteristics of the innate immune response?
Non specific
Typically very rapid
Involves recognising components that are common to many pathogens
1st line of defense mostly barrier based: skin, mucus, cilia, chemicals, acids etc
2nd line involves cells and other molecules: phagocytes, the complement, interferons, inflammation, fever, mast cells
What are the characteristics of the adaptive immune response?
Ability to distinguish between self and non self
Typically slow to develop and usually long lasting
Involves recognising components that are specific to each particular pathogen
Involves action of lymphocytes
Cellular and Hummoral responses.
Four key features: specificity, ability to distinguish self from non-self, diversity and immunological memory
What is the role of Macrophages in the immune system?
Macrophages are phagocytic and have function in both the innate and adaptive immune systems. Their role is to engulf and digest pathogens, cellular debris and infected cells.
Macrophages are often found stationed in areas where infection is likely to occur (special names)
- some like to circulate in blood and lymphatic vessels
- some can move through the blood vessels to the site of damage
- Phagocytes use defensins and other factors to kill pathogen after engulfing
What are the three phases of a defensive response?
Recognition: organism must discriminate between self and non-self
Activation: mobilisation of cells and molecules to fight invader
Effector: mobilised cells and molecules destroy invader.
How does inflammation occur?
Injury causes histamine release from mast cells, which are attracted to the area of injury. Histamine causes vessels to dilate and become leaky. Complement proteins move from blood to infected area and bind to and engulf pathogens. This attracts phagocytes/macrophages, which move from the blood to the infected area and bind and engulf pathogens.
Blood plasma also moves into infected area causing oedema.Platelets from blood release growth factors, which stimulates dermis cells to divide and heal the wound.
Pain is due to increased pressure of swelling and prostaglandins released from mast cells which increase the sensitivity of pain receptors
