Cell Structure and Function

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Cell Structure and Function. Chapter 6 and 7 AP Biology. Cell Theory. All living things are made of cells. Cells are the basic unit of structure and function in living things. All cells come from pre-existing cells. Eukaryotic vs. Prokaryotic Cells. - PowerPoint PPT Presentation

Transcript of Cell Structure and Function

Cell Structure and Function

Cell Structure and FunctionChapter 6 and 7AP BiologyCell TheoryAll living things are made of cells.Cells are the basic unit of structure and function in living things.All cells come from pre-existing cells.

The cell is the simplest component considered to be living. Cells can differ substantially from one another based on their function. (structure = function)2Eukaryotic vs. Prokaryotic CellsEukaryotic cells contain DNA in the nucleus. Prokaryotic cells contain DNA in a concentrated region called the nucleoid.

Which domains (ABE) are prokaryotes? Which are eukaryotes?We will talk more about prokaryotic cells later.

Cells share basic features: All cells are bound by a plasma membrane contains cytosol that has organelles suspended in it. All cells contain chromosomes which have genes in the form of DNAAll cells have ribosomes that make proteins according to instructions from genes.

Nucleus is bounded by a double membrane, nucleoid is not membrane enclosed.Eu = tru, karyon = kernel referring to the nucleus. Prok = before nucleus, reflecting that prokaryotic cells evolved before eukaryotic cells- tomorrow we will talk about how that happened

Within the cell is the cytoplasm. In eukaryotes, organelles are suspended in the cytosol of the cytoplasm. These organelles (with the exception of the ribosome) are not found in the prokaryotic cell. Prokaryotes are generally much smaller than eukaryotes. 3The Plasma MembranePlasma Membrane- a selective barrier (semipermeable) that allows passage of enough oxygen, nutrients, and wastes to and from the cell. The plasma membrane is a lipid bilayer embedded with diverse proteins.

The logistics of carrying out cellular metabolism (coded in the DNA) sets lower limits on cell size. Metabolic requirements also impose theoretical upper limits on cells size At the boundary of the cells, the plasma membrane allows passage of nutrients. These organelles have a specialized structure and function. (cytosol is the fluid like portion of the cytoplasm)

4Surface Area to Volume RatioAs you ___________ the cell size, you ____________ the surface area to volume ratio, which ___________ the efficiency of transport across the cell membrane.

Surface Area to Volume Ratio

For each square unit of membrane, only a limited amount of substance can cross per second, so the ratio of surface are to cell volume is critical. As a cell, or an other object increases in side, its volume grows proportionately more than its surface area. Thus a smaller object has a greater surface area to volume ratio.

Do larger organisms have larger cells? No- just more of them. The need for a sufficiently large surface area to volume ratio explains the microscopic size of most cells, and how some cells, such as nerve cells, are long and skinny. Some cells that need to be very good and moving materials such as intestinal cells. They have long thin projections called microvilli which increase surface area without much increase in volume. RBC also have depressed shape to help transport Oxygen.

In addition to the outer membrane, the eukaryotic cell has lots of internal compartments or organelles that faciliate specific functions. Each type of membrane has a unique compostion of lipids and proteins suited tot hat membrane specific functions. For example, enzymes embedded in membranes of the organelles called mitochondria, function in cell respiraiton.

6Animal Cell

Plant CellNucleus: Information CentralNucleus- contains cellular DNA which includes most of the genes in the cell. The nucleus is surrounded by the nuclear envelope.The nuclear envelope is a double membrane made of 2 lipid bilayers. Includes pore structures that help regulate things entering and exiting the nucleus.Nuclear Lamina- a net of protein filaments that maintain shape of nucleus and support nuclear envelope.

**Most of the genes in the cell? Where are the other genes? Where there is more DNA! Where is that? Mitochondria and chloroplast. The nucleus is usually the most conspicuous organelle in the cell (that means the one you can see the best- because it is usually the largest). Nuclear pores are lined with proteins called the pore complex that actually helps with movement in the nucleus.

Lipid bilayer includes proteins.

Also thought to be a nuclear matrix, protein fibers extending through the inside of the nucleus that helps organize genetic material so it functions efficiently.8Nucleus: Information CentralChromosomes- structures that carry genetic information (DNA). Each chromosome contains one long DNA molecule.Each eukaryotic species has a distinct number of chromosomes.Chromatin- the complex of DNA and protein making up chromosomes. Nucleolus- helps synthesize rRNA (ribosomal RNA) and ribosomes.

Within the nucleus, DNA is organized into discrete units called chromosomes.The DNA molecule is associated with many proteins. Some of them help coil the DNA molecule of each chromosome, reducing its length and allowing it to fit into the nucleus.

When the cell is not dividing, chromatin is a diffuse mass, and chromosomes cannot be distinguished from one another. When cells begin to divide, the chromatin condenses, and chromosomes become visible.

Fruit flies have 8 chromosomes.

Sometimes there are more than 1 nucleoli. Proteins enter the nucleolus from the cytoplasm and 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 subunit and a small subunit can assemble into a ribosome.9

*What else do you see in this picture of the nucleus that wasnt discussed in the others? RER and ribosomes

3 places ribosomes are found- on nucleus, on RER, and free floating in the cytoplasm.10Ribosomes: Protein FactoryRibosomes- made of rRNA and proteins- carry out protein synthesis. Ribosomes exist as either free ribosomes (suspended in cytosol) or bound ribosomes (attached to the Rough ER or nuclear envelope)

The nucleus helps direct protein synthesis by synthesizing mRNA according to instructions in the DNA. The mRNA is then transported to the cytoplasm where ribosomes translate the mRNA genetic message into the primary structure of a specific polypeptide.

Cells that have high rates of protein synthesis, have a higher number of ribosomes, which also make them more likely ot have more or more prominent nucleoli, b/c nucleoli help make ribosomes. ***What kind of cells would these be? Muscle cells. Pancreas cells have a few million ribosomes. They secrete digestive enzymes.

Bound and free ribosomes are structurally identical and they can alternate between the two roles. Most of the proteins made on free ribosomes function in the cytosol (ie: enzymes that catalyze reactions to breakdown sugar), whereas bound ribosomes generally make proteins that are destined for insertion in membranes, or for export from the cell (secretion).

11Endoplasmic Reticulum: Biological FactoryEndoplasmic Reticulum- consists of membranous tubules, and sacs, called cisternae. Smooth ER- lacks ribosomes. Functions lipid synthesis, detoxification, and storing calcium ions.Rough ER- has ribosomes on surface. Continuous with the nuclear envelope. Synthesizes glycoproteins and other secretory proteins.Endomembrane system- includes nuclear envelope, ER, golgi, lysosomes, and vassicles and vacuoles and the plasma membrane

Smooth- helps synthesize oils, phospholipids (membranes) and steroids (sex hormones- testosterone and estrogen).***considering that the smooth ER is used in detox, what organs in the body might contain a large amount of smooth ER? (liver) what other cells might contain lots of smooth ER? (sex cells- sperm and egg, cells in the ovaries and prostate.Alcohol and some other drugs increase the rate of smooth ER proliferation, which causes quicker detox and requires more of the substance to experience the same effect. This could ultimately lessen the effect of antibiotics and other medications (because of increased tolerance). Part of the way that the smooth ER detoxifies is by adding a hydroxyl group*What is a hydroxyl group? Is it polar or non polar? What does that mean about its solubility? This makes them easier to flush from the body.Calcium ions are important for muscle contraction.

Rough- many cells secrete proteins produced by ribosomes attached to rough ER. For example, certain pancreatic cells synthesize the protein insulin in the ER and secrete to bloodstream. As a polypeptide chain grows from an ER ribosome, it is threaded into the lumen of the ER through a pore in the ER membrane (made of protein complexes) When polypeptide enters lumen it folds into native shape. (Discuss protein folding again- chaperonins). Most proteins synthesize are glycoproteins. Carbohydrate attached to protein. This occurs by enzymes in ER membrane.

The RER is responsible for making its own membrane. Like the smooth ER, it also makes membrane phospholipids- also transported via vesicles.

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After secretory proteins are formed, ER keeps them separate by moving them to the transitional ER. They depart wrapped in the membranes of a vesicle.13Golgi Apparatus: Shipping and ReceivingGolgi Apparatus- made of flattened membranous sacs called cisternae. Has 2 sides the cis face (receiving) and the trans face (shipping).

When leaving ER, many transport vesicles travel to the Golgi- sorts, receives, ships, and some manufacturing. Golgi has structural directionality- stacks on opposite sides differ in thickness and molecular composition. Cis face is usually locatd near the ER as much of the receiving is from the ER (via transport). A vesicle that comes from the E