Ap Biology- A Tour of the Cell

16. A second function of lysosomes is to recycle cellular components in a process called autophagy. Describe this process.

Autophagy is when lysosomes use their hydrolytic enzymes to recycle the cell's own organic material. During autophagy, a damaged organelle or small amount of cytosol becomes surrounded by a double membrane, and a lysosome fuses with the outer membrane of this vesicle. The lysosomal enzymes dismantle the inner membrane and the enclosed material, and the resulting small organic compounds are released to the cytosol for reuse. With the help of lysosomes, the cell continually renews itself.

Plant cells have

Cell wall: protect plant, maintain shape Composed of cellulose Plasmodesmata: channels between cells to allow passage of molecule

Ribosomes

Function: protein synthesis Composed of rRNA + protein Large subunit + small subunit

Nucleus

Function: control center of cell Contains DNA Surrounded by double membrane (nuclear envelope) Continuous with the rough ER

Lysosomes

Function: intracellular digestion; recycle cell's materials; programmed cell death (apoptosis) Contains hydrolytic enzymes Lysosome is a membrane sac of hydrolytic enzymes that many eukaryotic cells used to digest (hydrolyze) macromolecules that contain an acidic pH (0-6.9). Hydrolytic enzymes and lysosomal membrane are made by rough ER and then transferred to the Golgi apparatus for further processing digest damaged cells or nutrients

Mitochondria

Function: site of cellular respiration Double membrane: outer and inner membrane Cristae: folds of inner membrane; contains enzymes for ATP production; increased surface area to ↑ ATP made Matrix: fluid-filled inner compartment-kerbs cycle electron transport =inner membrane-cristae hugher folds=increased productivity

CHLOROPLASTS

Function: site of photosynthesis Double membrane Thylakoid -highly folded membrane compartments -disks in stacks (grana); stroma (fluid) Contains chlorophylls (pigments) for capturing sunlight energy -membranes contain chlorophyll pigments that comprise the photosystems and electron transport proteins can be found between photosystems embedded in thylakoid membranes light dependent reactions folding of internal membrane increases efficiency of reactions stroma-liquid between the inner chloroplast membrane and outside thylakoids calvin cycle occurs here

VACUOLES

Function: storage of materials (food, water, minerals, pigments, poisons) Membrane-bound vesicles Eg. food vacuoles, contractile vacuoles Plants: large central vacuole -- stores water, ions

Golgi Apparatus

Function: synthesis & packaging of materials (small molecules) for transport (in vesicles); produce lysosomes Series of flattened membrane sacs (cisternae) Cis face: receives vesicles Trans face: ships vesicles

PEROXISOMES

Functions: break down fatty acids; detox alcohol Involves production of hydrogen peroxide (H2O2)

gap junctions

Gap junctions: channels through which ions, sugar, small molecules can pass

11. The rough ER is studded with ribosomes. As proteins are synthesized, they are threaded into the lumen of the rough ER. Some of these proteins have carbohydrates attached to them in the ER to form glycoproteins. What does the ER then do with these secretory proteins?

After the rough ER forms secretory proteins are formed, the ER membrane keeps them separate from proteins in the cytosol, which are produced by free ribosomes. Secretory proteins depart from the ER wrapped in the membranes of vesicles that bud like bubbles from a specialized region called transitional ER.Vesicles in transit from one part of the cell to another are called transport vesicles.

What are microvilli? How do these structures relate to the function of intestinal cells?

Microvilli are thin projections on each cell surface that increase surface area without an extreme increase in volume and aid the function of intestinal cells because they provide a high surface area to volume ratio which allows the intestine cells to exchange a high amount of materials (important in intestine cells as their function is to digest food). Microvilli are also made up of microfilaments or thin, solid rods that support the cells shape.

ENDOSYMBIONT THEORY

Mitochondria & chloroplasts share similar origin Prokaryotic cells engulfed by ancestors of eukaryotic cells Evidence: Double-membrane structure Have own ribosomes & DNA Reproduce independently within cell

Cytoskeleton

NETWORK OF PROTEIN FIBERS Function: support, motility, regulate biochemical activities

EXTRACELLULAR MATRIX (ECM)

Outside plasma membrane Composed of glycoproteins (ex. collagen) Function: Strengthens tissues and transmits external signals to cell

Eukaryotes

(Domain Eukarya): Protists, Fungi, Plants, Animals

tight junctions

2 cells are fused to form watertight seal

Why is it important that cells must be small?

Cells must be small to maintain a large surface area to volume ratio Large S.A. allows ↑ rates of chemical exchange between cell and environment Cells are so small so that they can maintain large surface area to volume ratio. Large surface area allows the increase of the rate of chemical exchange between cells and environment. If a cell grows past a certain limit not enough material will be able to cross the cell membrane which indicates that the SA wasn't large enough for the cells volume. when volume increases the demand for internal resources increases but can not be met by the smaller surface area

21. Animal cells have a centrosome that contains a pair of centrioles. Plant cells do not have centrioles. What is another name for centrosomes? What is believed to be the role of centrioles?

Centrosomes are regions that are often located near the nucleus and are considered a microtubule organizing center to compress resisting girders of cytoskeleton. Another word for centrosome is "microtubule-organizing center." Within the centrosome is a pair of centrioles, each composed of nine sets of triplet microtubules arranged in a ring. Although centrosomes with centrioles may help organize microtubule assembly in animal cells, many other eukaryotic cells lack centrosomes with centrioles and instead organize microtubules by other means.

ENDOMEMBRANE SYSTEM:

Creates Regulates protein traffic & performs metabolic functions create-package-modify-deliever products in and out of the cell nuclear envelope endoplasmic reticulum golgi apparatus Lysosomes Vesicles Vacuoles *Membranes of the system are related either through direct physical continuity or by transfer of membrane segments as tiny vesicles.

desmosomes

Desmosomes: "rivets" that fasten cells into strong sheets

Prokaryotes

Domain Bacteria & Archaea

ENDOPLASMIC RETICULUM (ER)

Network of membranes and sacs that produce proteins and lipids

15. One function of lysosomes is intracellular digestion of particles engulfed by phagocytosis. Describe this process of digestion. What human cells carry out phagocytosis?

Phagocytosis is the type of digestion where we engulf smaller organisms or food particles. The food vacuole formed in this way then fuses with a lysosome, whose enzymes digest the food. Digestion products, including simple sugars, amino acids, and other monomers, pass into the cytosol and become nutrients for the cell. Human cells also carry out phagocytosis, for example macrophages which are a type of white blood cells that help defend the body by engulfing and destroying bacteria and other invaders.

Plant cells only vs Animals Cells

Plant - central vacuoles -chloroplasts -cell wall of cellulose -plasmedesmata Animal -lysosomes -centrioles -flagella cilia desmosomes tight and gap junctions extracellular matrix

13. The transport vesicles formed from the rough ER fuse with the Golgi apparatus. Describe what happens to a transport vesicle and its contents when it arrives at the Golgi apparatus.

Products of the endoplasmic reticulum that are transported through vesicles are usually modified during their transition from the cis or same side of golgi facing the ER to the trans or part of golgi facing the opposite side of the ER. The vesicle adds its membrane and contents to the cis face and then engulfed by the golgi. The golgi then modifies the product as needed and then the new vesicle is formed from the trans face and then leaves the golgi.

Differences Between Prokaryotic and Eukaryotic Cells

Prokaryotic "before" "kernel" No nucleus DNA in a nucleoid Cytosol No organelles other than ribosomes Small size Primitive i.e. Bacteria & Archaea Eukaryotic "true" "kernel" Has nucleus and nuclear envelope Cytosol Membrane-bound organelles with specialized structure/function Much larger in size More complex i.e. plant/animal cell

Surface Example- plant cell

Root hairs: extensions of root epidermal cells; increase surface area for absorbing water and minerals

Surface Area Example- Small Intestine Animal Cell

Small Intestine: highly folded surface to increase absorption of nutrients Villi: finger-like projections on SI wall Microvilli: projections on each cell

A major difference between prokaryotic and eukaryotic cells is the location of their DNA. Describe this difference.

The difference between prokaryotic and eukaryotic cells is there location on DNA. In eukaryotic cells DNA is inclosed in an organelle called the nucleus which is bounded by a double membrane whereas in a prokaryotic cell, DNA is concentrated in a region called the nucleoid that is not membrane bound.

19. Recall the relationship of structure to function. Why is the inner membrane of the mitochondria highly folded? What role do all the individual thylakoid membranes serve?

The inner membrane contains folds called cristae that contain enzymes for ATP production that increases surface area to increase the amount of ATP made. In chloroplasts there is a membranous system in the form of flattened, inter connected sacs called thylakoids and they are stacked. Each thylakoid contains DNA and ribosomes in stroma or fluid outside the thylakoid. The structure of thylakoids enable the chloroplast to convert light energy to chemical energy efficiently by creating surface area.

5. Describe the nuclear envelope. How many layers is it? What connects the layers?

The nuclear envelope encloses the nucleus, separating it from the cytoplasm. It is a double membrane (inner and outer) so it consists of two layers lined with nuclear lamina. The double membrane are each a lipid bilayer with associated proteins and each protein structure called pore complex lines each pore and plays an important role in the cell by regulating the entry and exit of proteins and RNAs, as well as large complexes of macromolecules. Except at the pores, the nuclear side of the envelope is lined by the nuclear lamina that connects the layers. It is a netlike array of protein filaments (in animal cells, called intermediate filaments) that maintains the shape of the nucleus by mechanically supporting the nuclear envelope.

17. Explain how the elements of the endomembrane system function together to secrete a protein and to digest a cellular component.

The nuclear envelope is connected to the rough ER and smooth ER. Proteins are produced from DNA inside the nuclear envelope that are then formed in ribosomes in the rough ER. Membranes and proteins then produced in the endoplasmic reticulum are then moved to the golgi body in transport vesicles. The golgi then finalizes the product produced by removing the vesicle and adding or removing whatever is needed. The lysosome is then simply available for fusion with another vesicle for digestion. The transport vesicle then carries the product from the golgi (most likely protein) to the plasma membrane for secretion or to be transported out of the cell.

6. When are the nucleoli visible? What are assembled here?

The nucleoli are visible when the cell is not dividing and in the cells active protein synthesis. Ribosomal RNA is synthesized in the nucleoli or genes in the DNA. Also in the nucleolus, proteins imported from the cytoplasm are assembled with rRNA into large and small subunits of ribosomes. These subunits then exit the nucleus through the nuclear pores to the cytoplasm, where a large and a small subunit can assemble into a ribosome. Sometimes there are two or more nucleoli.

12. Besides packaging secretory proteins into transport vesicles, what is another major function of the rough ER?

The rough ER is a membrane factory for the cell meaning it grows in place by adding membrane proteins and phospholipids to its own membrane. As polypeptides destined to be membrane proteins grow from the ribosomes, they are inserted into the ER membrane and anchored there by hydrophobic proteins. The rough ER also makes membrane phospholipids like the smooth ER.

Connecting structure to function explain how the rough and smooth ER differ in functions?

The structure of both the rough Er and smooth ER result in the difference of their functions rough ER has ribosomes attached and is embended in the second membrane of the nuclear envelope that promotes its function of producing proteins whereas smooth ER is attatched to the rough ER with tibe like structure which results in its function of producing lipids and detoxifying the cell

Cell Wall

Three functions of the cell wall are protecting plants, maintaining shape, and supporting the cell in having specialized cells to hold up the plant against force of gravity. The cell wall consists of microfibrils made of polysaccharide cellulose are synthesized by an enzyme called cellulose synthase and secreted to the extracellular space, where they become embedded in a matrix of other polysaccharides and proteins. This combination of materials, strong fibers in a "ground substance" (matrix), is the same basic architectural design found in steel-reinforced concrete and in fiberglass. The primary cell wall is thin and flexible and between the primary walls of adjacent cells is the middle lamella or a thin layer rich of pectins (polysaccharides) and glues adjacent cells together (pectin is used as a thickening agent in jams and jellies). As cell grows so does its cell wall. The secondary wall between the plasma membrane and the primary cell wall and has a strong and durable matrix that affords the cell protection and support.

Bound Ribosomes

attached to ER, make proteins for export from cell

Chromatin

complex of DNA + proteins; makes up chromosomes

Nuclear pores

control what enters/leaves nucleus

Why do ribosomes and genomes reflect common ancestry of life?

each cell whether prokaryotic and eukaryotic needs a mechanisms to store and pass on genetic information by ribosomes sequencing proteins from mRNA that originates from DNA they produce proteins that help in the transferring of DNA

Free Ribosomes

float in cytosol, produce proteins used within cell

Smooth ER

no ribosomes on surface Function: synthesize lipids, metabolize carbs, detox drugs & poisons, store Ca2+

Nucleolus

region where ribosomal subunits are formed

Rough ER

ribosomes on surface Function: package proteins for secretion, send transport vesicles to Golgi, make replacement membrane compartemtalizes cell packaging newly synthesized proteins made by attached ribosomes

INTERCELLULAR JUNCTIONS (ANIMAL CELLS)

tight junctions, desmosomes, gap junctions