Transcript Cells Topic 2
Cells
Topic 2
Cell Theory
Schleiden, Schawnn, and Virchow Three components: (1) All living things are made of cells.
(2) (3) Cells are the basic unit of structure and function in living organisms.
Cells come from other cells.
Cells are microscopic
Most cells can’t be seen without a microscope Smallest cells are bacteria with diameters as small as .2 um. The bulkiest cells are bird eggs Longest human cells are certain muscle and nerve cells.
Most plant and animal cells (10 to 100 um)are ten times larger than most bacteria Refer to figure 4.2A on p. 54
Surface area to volume ratio of cells
The max. size of a cell is influenced by its requirement for enough surface area to obtain adequate nutrients and oxygen from the environment and dispose of wastes.
Cells must be very tiny to ensure the surface area is much larger than the volume for efficiency in a cell.
Prokaryotic Cells
Bacteria and Archaebacteria Very small cells, can only be seen with electron microscope Range from 1 to 10 um in length, about 1/10 the size of a eukaryotic cell Lack a nucleus and membrane bound organelles.
DNA is coiled in a nucleoid Have ribosomes, cell wall, capsule, pili, and flagella Reproduce asexually via binary fission
Prokaryotic cells
Cell Wall
Protects the cell and gives it shape
Capsule
Surrounds the cell wall and further protects the cell surface
Pili
Short projections used to attach bacteria to each other
Flagella
Longer projections used for movement
Ribosomes
Synthesize proteins
Eukaryotic Cells
Protists, Fungi, Plants, and Animals Have nucleus and membrane-bound organelles Much larger and more complex than prokaryotic cells.
Reproduce sexually and asexually
Eukaryotic Organelles General Function: Manufacturing
Nucleus
Control center of cell; contains most of the cell’s DNA
Nucleolus
Location where ribosomes are synthesized
Nuclear pore
Allows RNA to move in and out of nucleus
Ribosomes
Protein synthesis
Rough ER
Comprised of a network of tubes and flattened sacs.
Continuous with plasma membrane and nuclear membrane Site of protein synthesis (consists of ribosomes)
Eukaryotic Organelles General Function: Manufacturing
Smooth ER
Site of lipid and carbohydrate metabolism No ribosomes
Golgi Apparatus
Connected with ER; flattened disc-shaped sacs, stacked one on top of the other Modification, storage, and packaging of proteins.
“tags” proteins so they go to the correct destination.
protists)
Eukaryotic Organelles General Function: Breakdown
Digestion of nutrients, bacteria, and damaged organelles; destruction of certain cells during embryonic development
Peroxisomes
Diverse metabolic processes with breakdown of H 2 O 2 by-product
Vacuoles
Digestion (like lysosomes); storage of chemicals, cell enlargement; water balance
Eukaryotic Organelles General Function: Energy Processing
Chloroplasts
Conversion of light energy to chemical energy of sugars (site of photosynthesis)
Mitochondria
Conversion of chemical energy of food to chemical energy of ATP “Power House” of cell Bound by double membrane
Eukaryotic Organelles General Function: Support, Movement, and Communication
Cytoskeleton (including cilia, flagella, and centrioles in animal cells)
Maintenance of cell shape; anchorage for organelles; movement of organelles within cells; cell movement; mechanical transmission of signals from exterior of cell to interior.
Cell walls (in plants, fungi, and protists)
Maintenance of cell shape and skeletal support; surface protection; binding of cells in tissues
Eukaryotic Organelles General Function: Support, Movement, and Communication
Extracellular matrix
Binding of cells in tissues; surface protections; regulation of cellular activities
Cell junctions
Communication between cells; binding of cells in tissues.
Cell Membranes
Membranes provide the structural basis for metabolic order.
In eukaryotes, most organelle’s are made from membranes Many enzymes are built right into the membranes of these organelles
Selective permeability
Cell membranes control what goes in and out of the cell It allows some substances to cross more easily than others Cell membrane is amazingly thin
Membrane phospholipids form a bilayer
Lipids, mainly phopholipids, are the main structural components of membranes Phospolipid has a phosphate group and only two fatty acids Head, with a charged phosphate group, is hydrophillic Fatty acid tails are nonpolar and hydrophobic Thus, the tail end is pushed away by water, while the head is attracted to water
Phospholipid Bilayer
Phospholipids form a two-layer sheet called a phospholipid bilayer. Hydrophillic heads face outward, exposed to the water on both sides of a membrane Hydrophobic tails point inward, mingling together and shielded from water.
Phospholipid Bilayer
Phospholipid bilayer
Hydrophobic interior of the bilayer is one reason membranes are selectively permeable.
Nonpolar, hydrophobic molecules are lipid soluble can easily pass through membranes Polar molecules and ions are not lipid-soluble Ability to pass through membrane depends on protein molecules in the phospholipid bilayer.
Fluid Mosaic Model
Plasma membrane is described as a “Fluid Mosaic” Mosaic denotes a surface made of small fragments, like pieces of colored tile A membrane is considered “mosaic” because it has diverse protein molecules embedded in a farmework of phospholipids.
A membrane mosaic is “fluid” in that most of the individual proteins and phospholipids can can drift literally in the membrane
Tails of phospholipids are kinked.
Kinks make the membrane more fluid by keeping adjacent phospholipids from packing tightly together. In animal cells, the steroid cholesterol stabilize the phospholipids at body temperature and also keep the membrane fluid at lower temperatures. In a cell, phospholipid bilayer remains about as fluid as salad oil at room temperature.
Outside surface of plasma membrane has carbohydrates bonded to proteins and lipids in the membrane.
A protein with attached sugars is called a glycoprotein, whereas a lipid with sugars is called a glycolipid.
Function as cell identification tags that are recognized by other cells.
Significant for cells in an embryo to sort themselves to tissues and organs.
Also functions in the immune system to recognize and reject foreign cells.
Proteins make the membrane a mosaic of function
Mosaic refers both to positioning of proteins in membrane but also the activities of these proteins.
Proteins perform most of the functions of a membrane.
Different cells contain different sets of membrane proteins, and membranes within cells have unique proteins
Functions of Membrane Proteins
Attaching the membrane to cytoskeleton and external fibers Providing identification tags Forming junctions between adjacent cells Enzymes, functioning in catalytic teams for molecular assembly lines Receptors for chemical messengers from other cells Help move substances across the membrane, like water and glucose
Receptor proteins
Has a shape that fits the shape of a specific messenger, such as a hormone, just as an enzyme fits its substrate Binding of messenger to the receptor triggers a chain reaction involving other proteins, which relay the message to a molecule that performs a specific activity inside the cell (signal transduction)
Passive Transport
Diffusion of a substance across a biological membrane Diffusion is the movement of particles from high concentration to low concentration.
Moves with a concentration gradient No energy input required Eventually reaches equilibrium Molecules continue to move back and forth, but no net change in concentration will occur
Passive Transport
Necessary in our cells; lungs transport oxygen in red blood cells and carbon dioxide out via diffusion.
Small, nonpolar molecules that easily diffuse across plasma membranes
Passive Transport: Facilitated Diffusion
Many substances can’t diffuse freely across membrane because of their size, polarity, or charge Need the help of specific transport proteins in the membrane to move across the membrane Does not require energy Goes with the concentration gradient (high to low) Some sugars, amino acids, ions, and even water use facilitated diffusion Since water is polar, movement through hydrophobic interior is slow. Aquaporins allow for rapid transport into and out of cell.
Passive Transport: Facilitated Diffusion
Transport proteins (figure 5.15) Have to be specific to molecule moving across the membrane One example: provides a pore, or tunnel, for the passage of a solute Another example: protein binds molecule, changes shape, and releases molecule on the other side
Passive Transport: Osmosis
Osmosis: Diffusion of water molecules across a selectively permeable membrane With concentration gradient Requires no energy Tonicity Describes the tendency of a cell in a given solution to lose or gain water. Isotonic, hypertonic, and hypotonic
Passive Transport: Osmosis
Isotonic solution Equal concentration of solvent inside and outside of cell; water goes in and out Cell’s volume remains the same; equilibrium Hypertonic solution Solute concentration is lower inside cell (solvent concentration is higher inside cell) ;Water goes out Cell shrivels Causes plasmolysis in plant cells
Passive Transport: Osmosis
Hypotonic solution Solute concentration is greater inside the cell (solvent concentration is lower inside the cell); water goes in Cell swells and may lyse Causes cytolysis in animal cells Refer to figure 5.17
Passive Transport: Osmosis
Osmoregulation Control of water balance Method by which animals survive in hypertonic and hypotonic environments Example; freshwater fish have kidneys and gills that work constantly to prevent excessive buildup of water in the body
Active Transport
Requires that a cell expend energy to move molecules across a membrane Moves against the concentration gradient. ATP supplies the energy Moving molecules from low to high concentration
Active transport
Simple model, figure 5.18
1.
2.
3.
4.
Process begins when solute on cytoplasmic side of the plasma membrane attaches to a specific binding site on the transport protein.
ATP phoshporylates the transport protein Causing it to change shape in such a way that the solute is released on the other side of the membrane Phosphate group detaches and the transport protein returns to its original shape
Active Transport
Active Transport: Exocytosis
Exocytosis Used to export bulky materials Examples: insulin secretion into blood from pancreas; tear glands secrete salty sol’n containing proteins 1.
2.
A membrane-enclosed vesicle filled with macromolecules moves to the plasma membrane Vesicle fuses with plasma membrane 3.
Vesicles contents spill out of the cell
Endocytosis
Endocytosis A cell takes in macromolecules or other particles by forming vesicles or vacuoles from its plasma membrane Three kinds: phagocytosis, pinocytosis, receptor mediated endocytosis
Phagocytosis
Endocytosis
“cellular eating” Molecules of food move into the cell Example: amoeba Pinocytosis “cellular drinking” Molecules of fluid move into the cell; not specific Receptor-mediated endocytosis Highly specific; materials come in through indented pit in plasma membrane. Pit is lined with receptor proteins, pinch close to form vesicle containing molecules to be brought into the cell Example: cholesterol
Summary of Cell Transport
Cell Division
Cell Division Virchow: Cells can only come from preexisting cells In unicellular organisms, can reproduce an entire organism Allows multicellular organisms to reproduce asexually Basis of sexual reproduction sperm and egg Allows fertilized egg, or zygote, to develop into an adult organism Replaces worn-out or damaged cells Enables multicellular organism to grow to adult size
Prokaryotes reproduce by binary fission
Binary fission Process by prokaryotes reproduce by cell division.
Steps: Duplication of chromosomes and separation of copies.
Cell elongates Divides into two daughter cells
Chromosomes
Human cells carry about 20,000 genes to make 100,000 proteins.
Almost all genes are located in the nucleus Very small amount found in mitochondria Genes are found on DNA Chromatin Diffuse mass of long, thin fibers, not seen under the microscope, less tightly coiled Combination of DNA and protein
Chromosomes
Chromosomes Rod-shaped structure Coiled up, compact forms of chromatin Contains one long DNA molecule bearing hundreds or thousands of genes. DNA is attached to protein molecules (histones) Sister chromatids Each duplicated chromosome contains two identical copies.
Centromere The point by which two chromatids are joined.
What is the difference between
diploid haploid
and what are those numbers in and humans?
Diploid 2 sets of chromosomes (2n); 46 in humans Haploid 1 set of chromosomes (n); 23 in humans
What is the process called in Eukaryotes, when cells divide to make cells exactly alike (diploid)?
Mitosis!
What is the process called in Eukaryotes, when cells divide to make haploid cells?
Meiosis!
Cell Cycle
In your own body, millions of cells must divide every second to maintain the total number of about 100 trillion cells.
Some cells divide once a day, and some do not at all (mature muscle cells, liver cells, brain cells)
Interphase
Occurs when the cell is between cell division Interphase stages: G1: Cells grow to mature size S: DNA is copied G2: Cell prepares for division Cells exit the cell cycle via… G0: Cells do not copy DNA or prepare for mitosis, but are still alive (e.g. nervous system)
Interphase
Prophase
What does the cell look like?
Centrioles and spindle fibers appear Nuclear envelope disappears, and chromosomes are visible
Prophase
What happens to the DNA and nucleus?
Chromosomes form when chromatin tightens and coils Nuclear membrane breaks down and disappears What two things appear near where the nucleus was?
Centrioles and spindle fibers
Prophase
Metaphase
What does the cell look like?
Chromosomes move to the middle Where are the chromosomes during metaphase?
Middle of the cell
Metaphase
Anaphase
What does the cell look like?
Chromosomes move to the end of cell What happens to the chromosomes?
Chromosome splits at centromere into 2 chromatids and moves to end of cell
Anaphase
Telophase
What does the cell look like?
Cell starts to pinch in Nucleus starts to reform Chromosomes are at opposite ends What happens to the chromosomes and nucleus?
Nucleus forms back around single chromatids
Telophase
After Telophase
What is
cytokinesis
? Cytoplasm and contents (other organelles) divide What’s special about cytokinesis in plants? Cell wall also divides with new cell plate in middle
Growth Factors signal the cell cycle
Growth factors are the main signals that stimulate cell division Cells have a series of checkpoints that are regulated by proteins.
These checkpoints determine whether or not cell division will occur.
Cancer
Mutations in the genes of these checkpoint proteins may lead to cancer:
The uncontrolled growth of cells.
Tumor: an abnormally growing mass of body cells Benign tumor If abnormal cells remain at original site Can be problematic if disrupt certain organs, but usually easily removed by surgery Malignant tumor If abnormal cells spread into other tissues and body parts, interrupting organ function
Cancer
Metastasis Cancer that spreads via the circulatory system Carcinomas Cancer found in the external or internal coverings of the body; skin, lining of intestine Sarcomas Cancer found in tissues that support the body; bone and muscle Leukemias and lymphomas Cancer of blood forming tissues, bone marrow, spleen, and lymph nodes
Cancer
Usually caused by a loss of inhibitory factors (tumor suppressor genes), or an increase in growth factors (oncogenes).
Surgery, radiation, and chemotherapy are typical treatments
Cell Differentiation
During repeated cell division that lead from a zygote to a multicellular adult, individual cells must undergo differentiation
Become specialized in structure and function
Results from selective gene expression, the turning on and off of genes
Each differentiated cell expresses genes that allow the cell to perform certain functions:
Beta cells expressed genes that allow it to produce the hormone insulin
Cell Differentiation
About 50 cell division produce approximately 100 billion cells in an adult.
During the development of an embryo, the cells specialize to take on the roles of 220 different cell types. Some cells stop dividing at a certain point in the adult life, some continue to divide throughout lifespan Genes, either turned on or off, control the destined role of the cell.
Stem Cells
Adult Stem Cells (ACS) Cells present in adult tissues that generate replacemetns for nondividing diffrentiated cells.
multipotent Embryonic Stem Cells (ES cells) Harvested from the blastocyst Give rise to all the different kinds of specialized cells of the body pluripotent
Stem Cells
Induced Pluripotent Stems Cells (iPS) Stem cells created via de-differentiation of an adult cell (eg. Skin cell).
Pluripotent
Cloning
Nuclear transplantation is used: Replacing nucleus of an egg cell or zygote with the nucleus of an adult somatic cell.
After sever days, a blastocyst forms which may be used for many purposes If stem cells in blastocyst are used for the birth of a new individual: reproductive cloning Can be used to create genetically identical individuals for experimentation.
If stem cells in blastcyst are induced to form specialized cells: therapeutic cloning:
Used to make essential cells: beta cells to make insulin, dopamine neurons for Parkinson’s patients.