Sunday, December 13, 2009
Wednesday, December 9, 2009
Meiosis and Sexual Life Cycles
What is meiosis?
--> cell division that produces reproductive cells in sexually reproducing organisms (the nucleus divides into four hapoloid cells/nuclei)
What are the stages of meiosis?
meiosis I: prophase I, metaphase I, anaphase I, telophase I and cytokinesis (division of the cytoplasm)
meiosis II: prophase II, metaphase II, anaphase II, telophase II and cytokinesis
What are the differences between mitosis and meiosis?
Basically, meiosis reduces the number of chromosome sets from two (diploid) to one (haploid), whereas mitosis conserves the number of chromosome sets. Therefore, meiosis produces cells that differ genetically from their parent cell and from each other, whereas mitosis produces daughter cells that are genetically identical to their parent cell and to each other.
Facts:
- We inherit one set of chromosomes from our mother and one from our father
- In sexual reproduction, a single parent produces genetically identical offspring by mitosis
- Normal human somatic cells have 46 diploid chromosomes.
- The two cell divisions of meiosis produce 4 haploid daughter cells.
- Mutations are the original source for genetic variation.
JK Key terms:
Heredity (inheritance) = transmission of traits from one generation to next
Genetics = the scientific study of heredity
Clone = a group of genetically identical individuals
Gametes = reproductive cells
Somatic cells = any cell other than those involved in gamete formation
Karyotype = display of paired chromosomes (map of chromosomes)
Sex chromosomes = x and y, determine the sex
Autosomes = other chromosomes
Diploid cell= any cell with two chromosome sets (2n)
Haploid cell= any cell with a single chromosome set (n)
Summary:
A cell undergoing meiosis will divide two times; the first division is meiosis 1 and the second is meiosis 2. The phases have the same names as those of mitosis. A number indicates the division number (1st or 2nd):
meiosis 1: prophase 1, metaphase 1, anaphase 1, and telophase 1
meiosis 2: prophase 2, metaphase 2, anaphase 2, and telophase 2
In the first meiotic division, the number of cells is doubled but the number of chromosomes is not. This results in 1/2 as many chromosomes per cell.
The second meiotic division is like mitosis; the number of chromosomes does not get reduced.
The Cell Cycle
What are the results of cell division? + example
--> genetically identical daughter cells
--> example: hydra(budding)
What are the phases of the cell cycle?
--> Mitotic (M) phase usually includes mitosis and cytokinesis
--> interphase (G1 - first gap, S - synthesis, G2 - second gap)
Mitosis is usually broken down to 5 stages:
prophase, prometaphase, metaphase, anaphase, telophase
What is a checkpoint of the cell cycle?
It is a control point where stop and go-ahead signals can regulate the cycle.
Facts:
- Cells duplicate their genetic material before they divide.
- DNA is partitioned among chromosomes.
- Eukaryotic cell division consists of mitosis and cytokinesis.
- Animal cells carry out cytokinesis by cleavage, and plant cells from a cell plate.
- Cancer cells elude normal regulation and divide out of control, forming tumors.
Key terms:
genome = genetic information
chromosome = package of DNA
somatic cells = all body cells except the reproductive cells
gametes = reproductive cells
chromatin = a complex of DNA
sister chromatids = two chromatids containing the same DNA molecule
centromere = a region where 2 sister chromatids are attached
meiosis = cell division
cytokinesis = division of the cytoplasm
MPF = maturation-promoting factor, a protein complex required for a cell to progress from late interphase to mitosis (cyclin and a protein kinase when active)
growth factor = a protein released by certain cells that stimulates other cells to divide
mitosis phases
We have already discussed how the two main events of cellular reproduction are the copying of cellular components and the cleavage of the cell. These two events, copying and cleaving, represent the two larger phases of the cell cycle, interphase and Mitosis. Mitosis is the part of the cell cycle when the cell prepares for and completes cell division. During interphase, appropriate cellular components are copied. Interphase is also a time of checkpoints to make sure that the cell is ready to proceed into mitosis. Both of these two phases have further sub-divisions. Since the cell cycle is a "cycle" it has no distinct beginning or ending. Cells are continually entering and exiting the various phases of the cycle.
Cell Communication
cell junctions
[both animals and plants have cell junctions that allow muscles to pass readily between adjacent cells without crossing plasma membrane]
Explain the evolution of cell signaling!
Signaling in microbes has much in common with processes in multicellular mechanisms, suggesting an early origin of signaling mechanisms. Bacterial cells can sense the local density of bacterial cells by binding molecules secreted by other cells. In some cases, such signals lead to aggregation of these cells into biofilms.
What are three stages of cell signaling?
1. reception
2. transduction
3. response
What is apoptosis?
Apoptosis is a type of programmed cell death in which cell components are disposed of in an orderly fashion, without damage to neighboring cells.
Facts:
- In local signaling, animal cells may communicate by direct contact or by secreting local regulators, such as growth factors or neurotransmitters.
- The binding between signaling (ligand) and receptor is highly specific.
- Intracellular receptors are cytoplasmic or nuclear proteins.
- The behavior of testosterone is representative of steroid hormones.
- Most water-soluble molecules bind to specific sites on receptor proteins embedded in the cell’s plasma membrane.
Key terms:
Signal transduction pathway = series of steps when a signal on a cell’s surface is converted to a specific cellular response
Local regulators = influence cells in the vicinity
Hormones = chemicals for long-distance signaling
Ligand = a molecule that binds specifically to another molecule, usually a larger one
Cyclic AMP/ cAMP = cyclic adenosine monophosphate, a ring-shaped molecule made from ATP that is common intracellular signaling molecule (second messenger)
Receptor tyrosine kinase proteins = inactive monomers
Protein kinase = an enzyme that transfers phosphate groups from ATP to a protein
Adenylyl cyclase = an enzyme embedded in the plasma membrane; converts ATP to camp in response to extracellular signals
Scaffolding proteins = large relay proteins to which several other relay proteins are simultaneously attached
Apoptosis = a program of controlled cell suicide
Summary:
Signaling in microbes has much in common with processes in multicellular organisms, with processes in multicellular organisms, suggesting an early origin of signaling mechanisms. In local signaling, animal cells may communicate by direct contact or by secreting local regulators, such as growth factors or neurotransmitters. For signaling over long distances, both animals and plants use hormones. Earl Sutherland discovered how the hormone epinephrine acts on cells: the signal is transmitted by successive shape changes in the receptor and relay molecules.
The binding between a ligand and receptor is highly specific. The change of the receptor is often the initial transduction of the signal. A G protein-coupled receptor is a membrane receptor that works with the help of a cytoplasmic G protein. Ligand binding activates the receptor, which then activates a specific G protein, which activates another, propagating the signal along a signal transduction pathway. Another receptor in the plasma membrane is tryosine kinase. Specific signaling molecules cause ligand-gated ion channels in a membrane to open or close, regulating the flow of specific ions. Intracellular receptors are cytoplasmic or nuclear proteins.
Cascades of molecular interactions relay signals from receptors to target molecules in the cell.
Cell signaling leads to regulation of transcription or cytoplasmic activities.
Apoptosis is a type of programmed cell death in which cell components are disposed of in an orderly fashion, without damage to neighboring cells.
(video!)
Photosynthesis
What is photosynthesis? Give the equation!
photosynthesis equation
What is an autotroph?
Autotrophs are "self-feeders".
How does Ps relate to fall leaf colors?
Plants change their leaves color in the fall. Most leaves include the chlorophyll (green), xathophyll (yellow) and carotene (orange) pigments, but chlorophyll is much than the others. It covers other two. During fall, the strength of light is weaker and the temperature drops, too. Plants/leaves adopt to it by breaking down chlorophyll. N and Mg (building chlorophyll) are salvaged and moved into the stem for next year. Now other, accessory pigments are reflected the most and give leaves diverse “fall” colors.
Facts:
- Photosynthesis converts light energy to chemical energy of food!
- The light reactions convert solar energyto the chemical energy of ATP and NADPH.
- The Calvin Cycle uses ATP and NADPH to convert carbon dioxide to sugar.
- Alternative mechanisms of carbon fixation have evolved in hot, arid climates.
- All green parts of plants have chloroplasts.
Key terms:
Autotrophs – self feeders
Heterotrophs – obtain their organic material by the second major mode of nutrition, unable to make their own food
Chlorophyll – the green pigment within chloroplasts
Mesophyll – the tissue in the interior of the leaf
Stroma – the dense fluid within the chloroplasts
Thylakoids – interconnected membranous sacs
Grana – thylakoid coumn
Photophosphorylation – adition of a phosphate group to ADP
Carbon fixation – initial incorporation of carbon into organic compounds
Wavelength – the distance between the crest of electromagnetic waves
Summary:
Photosynthesis is a process in which light energy is converted to chemical energy and used to produce organic compounds. In plants, photosynthesis occurs within the chloroplasts. Photosynthesis consists of2 stages, the light and the dark reactions. The light reactions convert light into energy (ATP, NADPH) and the dark reactions use energy and carbon dioxide to produce sugar.
Extra: light dependant reaction of photosynthesis video!
Cellular Respiration [Harvesting Chemical Energy]
What is cellular respiration and its equation?
It is the process of releasing energy from food.
Equation: C6H12O6 + 6O2 --> 6CO2 + 6 H2O
(The energy is released from the bonds)
Name the 3 main stages of cell respiration and explain briefly
1) glycolysis
purpose: To split glucose and produce NADH and ATP
a) Energy investment phase --> G3P (glycerolaldahyde, 3C sugar)
b) Energy harvest (payoff) phase --> pyruvate
--> doesn't require O2
location: mitochondria matrix
acetyl CoA --> acetyl coenzime A; the entry compound for the krebs cycle in celll respiration, formed from a fragment pyruvate attached to a coenzime
oxidative phosphorylation (electron transport chain)
purpose: converting NADH and FADH2 into ATP
ETC --> mitochondrial inner membrane (control of the energy transport)
requirements: NADH or FADH2, ADP, O2
ATP synthase is a general term for an enzyme that can synthesize adenosine triphosphate (ATP) from adenosine diphosphate (ADP) and inorganic phosphate by using some form of energy. This energy is often in the form of protons moving down an electrochemical gradient, such as from the lumen into the stroma of chloroplasts or from the inter-membrane space into the matrix inmitochondria. The overall reaction sequence is:
- ADP + Pi → ATP
- The energy stored in the organic molecules of food ultimately comes from the sun.
- To keep working, a cell must regenerate ATP.
- The electron transport chain is a collection of molecules embedded in the inner membrane of the mitochondria in eukaryotic cells.
- In prokaryotic cells, the krebs cycle occurs in the cytosol.
- At the end of electron transport chain, electrons are passed to oxygen, reducing it to water.
Key terms:
Aerobic respiration – the most relevant and efficient catabolic pathway
Anaerobic – no O2
Cellular respiration – both aerobic and anaerobic processes
Oxidation – loss of electrons and energy
Oxidizing agent – the electron acceptor
Reduction – gain of electrons and energy
Reducing agent – the electron donor
NAD+ - electron carrier/acceptor, oxidizing agent in glycolisis
Chemiosmosis – energy-coupling mechanism
Fermentation – a way of harvesting chemical energy without using either oxygen or any ETC (no cell respiration)
Summary:
Cellular respiration allows organisms to use (release) energy stored in thechemical bonds of glucose. The energy in glucose is used to produce ATP. Cells use ATP to supply their energy needs. Cellular respiration is therefore a process in which the energy in glucose is transformed to ATP.
In respiration, glucose is oxidized and thus releases energy. Oxygen is reduced to form water. The carbon atoms of the sugar molecule are released as carbon dioxide.
The complete breakdown of glucose to carbon dioxide and water requires three major steps:
1)glycolysis; 2) krebs cycle; 3) oxidative phosphorylation
Glycolysis produces two ATP. Thirty-four more ATP are produced by aerobic pathways if oxygen is present.
Extra: Glucose Breakdown: RAP!
Wednesday, October 14, 2009
An Introduction to Metabolism
What is metabolism?
Metabolism is the collection of chemical reac
tions that occur in an organism.
What is energy and which are the forms of energy?
Energy is capacity to cause change.
Kinetic energy = Energy of action or motion
Potential energy = stored energy or capacity to do work
Energy of activation = Energy needed to convert potential energy into kinetic energy
How can regulation of enzyme help control metabolism?
Enzymes speed up metabolic reactions by lowe
ring energy barriers.
They are biological catalysts that cause the rate of a chemical reaction to increase.
Facts:
- Every chemical reaction between molecules involves both bond breaking and bond forming.
- The quantity of energy in the universe is constant, but quality is not.
- Energy released from ATP drives anabolic reactions.
- Energy from catabolic reactions "recharges" ATP.
- Each chemical reaction in the cell requires its own enzyme.
Key words:
Metabolism = the totality of an organism’s chemical reactions
Energy = the ability to do work
Kinetic energy = energy of motion / action
Potential energy = tored energy or capacity to do work
Energy of activation = Energy needed to convert potential energy into kinetic energy
Entropy = measure of disorder
Free energy = portion of a system’s energy that can perform work when temperature and pressure are uniform throughout the system, as in a living cell
Exergonic reaction = release of free energy
Endergonic reaction = absorbs free energy
Energy coupling = a key feature in the way cells manage their energy resources to do work (chemical, transport, mechanical)
Phosphorylated = the recipient of the phosphate group
Summary:
Energy, the ability to do work can be kinetic, potential or activation energy. The laws of energy transformation say that it cannot be cr
eated or destroyed, only transfered and transformed. The second law states that spontaneous changes, those requiring no outside input of energy, increase the entropy (disorder) of the universe.
Free energy is the energy that can preform work when temperature and pressure are uniform throughout the system, as in a living cell. We can think of free energy as a measure of systems' instability - its tendency to change to a more stabile systems. The term that describes maximum stability is equilibrium.
Based on free energy changes, chemical reactions c
an be classified as either exergonic (energy released) or endergonic (energy absorbed).
ATP powers cellular work by coupling exergonic reactions to endergonic reactions.
Enzymes speed up metabolic reactions by lowering energy barriers. Their regulation helps control metabolism. An enzyme catalyzes a reaction by lowering the activation energy barrier, enabling the reactant molecules to absorb enough energy to reach the transition state even at moderate temperatures.
(diffusion, the relationship of free energy to work capacity, stability and spontaneous change)
Extra:
how ATP works (video)
Monday, October 12, 2009
Membrane Structure and Function
What is a plasma membrane and how is it composed?
It is membrane at the boundary of every cell, composed of a phospholipid bilayer and proteins.
What is meant by fluid-mosaic model of a membrane?
In 1972, S.J.Singer and G. Nicolson proposed that membrane proteins are dispersed, individually inserted into the phospholipid bilayer with their hydrophilic regions protruding. This molecular arrangement would maximixe contact of hydrophilic regions of proteins and phospholipis with water in the cytosol and extracellular fluid, while providing their hydrophobic parts with a nonaqueous environment. In this fluid-mosaic model, the membrane is a mosaic of protein molecules bobbing in a fluid bilayer of phospholipids.
What are protein functions in the membrane?
- Transport
- Enzymatic activity
- Receptor sites for signals
- Cell adhesion
- Cell-cell recognition
- Attachment to the cytoskeleton
Facts:
- A membrane is held together primarily by hydrophobic interactions (much weaker than covalent bonds).
- More than 50 kinds of proteins have been found so far in the plasma membrane of red blood cells.
- The Davson-Danielli sandwich model of the membrane has been replaced by the fluid mosaic model, in which amphipathic proteins are embedded in the phospholipid bilayer.
- Short chains of sugars are linked to proteins and lipids on the exteror side of the plasma membrane, where they interact with surface molecules of other cells
- One solute’s “downhill” diffusion drives the other’s “uphill“ transport
Key terms:
Integral proteins = transmembrane protein eith hydrophobic regions that extend into and often completely span the hydrophobic interior of the membrane and with hydrophilic regions in contact with the aqueous solution on either side of the membrane
Peripheral proteins = proteins loosely bounded to the surface of a membrane or to part of an integral protein and not embedded in the lipid bilayer
Glycolipids = molecules formed of membrane carbohydrates covalently bonded to lipids
Glycoproteins = membrane carbohydrates + proteins
Aquaporins = channel proteins (facilitate the passage of water molecules through the membrane)
Diffusion = the movement of molecules of any substance so they spread out evenly into the available space (passive transport)
Osmosis = the diffusion of water
Facilitated diffusion = the spontaneous passage of molecules or ions across a membrane with the assistance of specific transmembrane transport proteins
Passive transport = no energy required / invested
Active transport = energy required
Summary:
The Davison Danielli sandwich model of the cell membrane (1935) has been replaced by the fluid mosaic model, in which amphipathic proteins are embedded in the phospholipid bylayer. Proposed by Singer and Nicolson in 1972.
The plasma membrane controls the processes of the exchange of molecules and ions of the cell with its surrounding.
Besides enzymatic activity, receptor sites for signals, cell adhesion, cell-cell recognition and attachment to the cytoskeleton, the protein function in the membrane is transport, but the question is how do materials get across the cell membrane?! ... There are two ways of transport and these are passive and active. Passive (diffusion, osmosis, facilitated diffusion) does not require cellular energy. The way of movement of the atoms and ions is from higher to lower concentration until the equilibrium is reached. Active transport (Carrier-Mediated, endocytosis, exocytosis), unlike passive, requires cellular energy (ATP).
Extra:
osmosis (video)
Sunday, October 11, 2009
A Tour of the Cell
What is a cell?
The cell is the fundamen
tal unit of life (for biology, as the atom is fundamental for chemistry). All organisms are made of cells --> basic units of structure and function. Each action of an organism begins at the cellular level.
What do biologists use to study cells?
To study cells, biologists use microscopes and the tools of biochemistry.
- light microscopes (LM) - uses visible light to illuminate the objects
- electron microscopes (EM) - uses beams of electrons instead of light
.. scanning electron microscope (EEM)- surface view
.. transmission electron microscope (TEM) - look inside
What is the difference bet
ween animal and plant cell?
- Plant cells have cell walls, a central vacuole, plasmodesmata and chloroplasts (animal cell x).
- Animal cells have Lysosomes, Centrosomes with centrioles and flagella (sometimes present in plan
t sperm)
Facts:
- The cell is fundamental to the living systems of biology as the atom is to chemistry.
- The light microscope offers
advantages in studying living cells (methods used in electron microscopy kill the cells).
- Larger organism do not generally have larger cells than smaller organisms - simply more cells.
- Improvements in microscopy that affect the parameters of magnification, resolution, and contrast have catalyzed progress in the study of cell structure.
- All cells are bounded by a plasma membrane.
Key terms:
cell = basic functional unit of all living things
lipid bilayer = double phospholipid membrane --> outer hydrophilic heads and hydrophobic tails pointing towards inside
organelles = bodies within the cytoplasm that serve to physically separate the various metabolic reactions that occur within the cells
nucleus = "brain" of the cell
ribosome = consisting of RNA
endoplasmic reticulum = stacks of flattened sacs involved in the production of various materials
golgi apparatus = group of flattened sacs arranged like a stack of bowls, functioning to modify and package proteins and lipids into vesicles
lyzosomes = vesicles from a golgi apparatus that contain digestive enzymes
mitochondria = organelles that carry out aerobic respiration
chloroplasts = organelles that carry out photosynthesis
flagella and cilia = structures that protrude from the cell membrane and make wavelike movements
Summary:
Although the cell is the smallest unit of life, it is by no means simple. The human body is made up of tens of trillions of cells, which have developed a highly synchronized set of components to carry out the processes that keep the organism alive, allow it to reproduce and adapt to changing environments.
Organelles are bodies within the cell cytoplasm that serve to physically separate the various metabolic reactions that occur within the cell. Some of them are : the nucleus, ribosomes, endoplasmic reticulum, golgu apparatus, lysosomes, peroxisomes, mitochondria, chloroplasts, microtubules, fagella and cilia, centrioles, cell walls, vacuoles and vesicles...
Extra:
animal cell (video)
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