Ribosomes
What’s most important?
·Ribosomes are small dot-like structures in cells.
·Ribosomes are often associated closely with endoplasmic reticulum(ER), forming rough ER.
·Ribosomes are the site of protein synthesis in cells.
Structure
Ribosomes are made up of proteins and ribonucleic acid(RNA).
These molecules are arranged into two subunits called the large and small subunits. These subunits are attached to each other and together form the entire ribosome. When viewed through a light microscope the ribosomes appear as dots, they are very small and the subunits can not be seen.
Function
The only function of ribosomes is to build proteins. The plan for the protein in the form of mRNA passes through a groove in the ribosome. The ribosome “reads” the plan and assembles the proper sequence of amino acids to build the protein.
There are two kinds of ribosomes, those attached to the endoplasmic reticulum and those floating in the cell cytoplasm. Attached ribosomes make proteins that are used in the ER or transported within the ER. Free ribosomes make proteins that are used in the cytoplasm.
The details of how ribosomes make proteins are presented in the “Protein Synthesis” section of your biology book. This is a complicated process beyond the scope of this document.
The Term Paper on Structure And Function Of Eukaryotic Cell Organelles
... exit for the ribosome subunits. The chromatin that surrounds the nucleolus contains both DNA and proteins. When the cell is dividing the ... is the site of first stage protein modification. The ribosomes attached to the RER synthesise proteins, which then enter the cisternal space. ... Between the layers the proteins are moved through the gaps by small vesicles. When a protein has been modified correctly, ...
Details
Ribosomes are made in the nucleus of the cell.
Ribosomes are about 60% rRNA by weight.
A ribosome can make the average protein in about one minute.
Ribosomes often line up in clusters called polyribosomes, these are connected by the mRNA and all make the same protein. In this way the cell can make many copies of a protein very fast.
The cell or plasma membrane was once thought to be a simple barrier that kept the contents of the cell, the cytoplasm, contained. It serves as a gateway which helps to control materials going in and out of the cell. With more research, it turns out the cell membrane is very important in a wide range of cell activities including functions related to cancer and AIDS.
Structurally, the membrane is a lipid bilayer. What this means is that, under the electron microscope two separate layers can be seen. The layers are composed of a two part molecule called a phospholipid. The lipids (fatty acids) are “water fearing” (hydrophobic) molecules. Just try to mix oil and water to see what that means. The phosphate end is water loving (hydrophilic).
The membrane forms when the phosphate ends point out, attracted to the watery environment of the cell and the lipid ends point in, trying to avoid the water. Embedded in this lipid bilayer are several different kinds of protein molecules. Click here to see a diagram of a cell membrane.
The membrane does not form a solid sheet like a piece of cellophane. Its structure is called a “fluid mosaic” because pieces of the membrane can rip off without creating a hole or merge in with other membranes. The membranes surrounding the internal organelles, such as the endoplasmic reticulum, Golgi bodies, lysosomes and vacuoles use this action to help carry out their functions.
Jobs of the Cell Membrane
I. Transport
The cell membrane is the border surrounding the entire cell. Obviously if food, oxygen, water and wastes are going to move in and out of the cell there has to be some way to do that. Are there holes in the membrane? What if something is too big to go through the membrane? What about things that don’t mix with lipids such as those found inside the membrane? Read here about the ways that materials can move in and out of cells.
The Essay on Metabolism: Cell Membrane And Protein Synthesis
Kinetic energy is energy in action, while potential energy is stored energy. Structurally variant atoms, which have the same number of protons (and electrons), but differ in the number of neutrons they contain Atomic weight of an element is approximately equal to the mass number of its most abundant isotope. is based on the concentration of H+ ions. Which of the following is not a subatomic ...
2. The Immune System
If cells are going to fight off germ invaders they have to have a way to recognize which cells belong to you and which cells don’t. Cells identify themselves by marker molecules on the cell membrane.
Cells that don’t belong to you (even if it is in a transplanted heart!) get attacked and destroyed. Even your own cells, if they change somehow (like when they get cancer), can be destroyed by your immune system. Click here to find out more about your immune system.
3. Cell Junctions
What would you look like if your cells didn’t stick together? What holds cells together? How does information pass from cell to cell.
The cell membrane
the nucleus
The nucleus is the brain of eukaryotic cells. It is only present in eukaryotic cells (which are eukaryotic because they have a nucleus) and there is only one of these organelles in each cell. Usually the nucleus is round and is the largest organelle in the cell. It is surrounded by a membrane, called the nuclear envelope, which is similar to the cell membrane that encloses the entire cell. The envelope is riddled with holes, called nuclear pores, that allow specific materials to pass in and out of the nucleus, just like proteins in the cell membrane regulate the movement of molecules in and out of the cell itself. Attached to the nuclear envelope is the endoplasmic reticulum. The nucleus is surrounded by the cytoplasm inside a cell. The nucleus is the pink half-sphere in the center of the cell.Source: Audesirk, Gerald, and Audesirk, Teresa. Biology: Life on Earth.
DNA to proteinSource: http://cellbio.utmb.edu/cellbio/ribosome.htm The nucleus houses the DNA (deoxyribonucleic acid) which stores genetic information for a cell. The DNA contains instructions for the production of the cell’s proteins and for reproduction. To construct proteins, the DNA is copied to messenger RNA (ribonucleic acid) in the process called transcription. The mRNA goes to the ribosomes, either in the nucleus or in the endoplasmic reticulum, where the actual construction of the proteins takes place. Structurally, the nucleus is composed of three main parts, the nucleolus, the nuclear envelope, and the chromatin. The nucleolus contains ribosomes, RNA, DNA, and proteins. The nucleolus has some of the ribosomes that synthesize proteins (others are in the endoplasmic reticulum).
The Essay on Nuclear Protein Membrane Lamin Envelope Cell
1. The nuclear envelope is a double membrane extension of the rough endoplasmic reticulum containing many nuclear pore complexes. The lipid bilayer of the inner nuclear membrane is supported by the nuclear lamina, a mesh work of lamin filament located adjacent to the inside face of the nuclear envelope. (Lodish et al 1997) The lamina is proposed to be involved in both organizing chromatin and in ...
The chromatin (meaning “colored substance”) contains DNA and proteins formed into packets of code called chromosomes. When the cell divides, the chromosomes fold up on themselves, getting wider. The nuclear envelope is important because it allows the nucleus to control the rest of the cell, such as by sending out ATP. The envelope will let molecules like ATP through but will keep other things in or out, so the nucleus is isolated from the cytoplasm.
Structure of the Nucleus:
Source: http://cellbio.utmb.edu/cellbio/nucleus.htm
Bibliography:
Audesirk, Gerald, and Teresa Audesirk. Biology: Life on Earth. Upper Saddle River: Prentice Hall, 1999.
Childs, Gwen V. “Cell Biology Topics.” 30 Dec. 1999. 14 Feb. 2000.
http://cellbio.utmb.edu/cellbio/nucleus.htm
Childs, Gwen V. “Cell Biology Topics.” 30 Dec. 1999. 14 Feb. 2000.
http://cellbio.utmb.edu/cellbio/ribosome.htm
Ferguson, John B. “Nucleus (biology).” Encarta Encyclopedia 14 Feb. 2000.
http://encarta.msn.com/encarta/Contents.asp?z=2&br=0&pg=2&ti=033D5000&hs=cell+nucleus&tr=11&pos=100.
Cytoplasm
http://www.dcn.davis.ca.us/~carl/cytoplsm.htm
Structure and Functions
Cytoplasm is the watery environment inside the cell. This extracellular fluid consists of all of a cell’s internal contents, and is mostly made of water. Cytoplasm includes salts, an assortment of organic molecules, including many enzymes that catalyze reactions, as well as water. The cytoplasm is seperated from the wattery extracellular fluid, which is outside, by the plasma membrane. It contains discrete membrane-enclosed structures called organelles. Each of the organelles performs a specific cellular function. They also have specialized proteins that provide an intracellular support system.
The Essay on The Structure and functions of proteins
Proteins are made up of long chains of amino acids, just a chain of ami. tacids makes up the primary structure. The secondary structure is formed by hydrogen bonds joining the chains in certain places to make an alpha helix or a beta sheet. The tertiary structure is formed by even more folding and joining of the chains to make a globular mass or fibrous mass. An example of this would be a carrier ...
The cytoplasm is in all cells, where metabolic reactions occur. Cytoplasm can be found in eukaryotic cells, which are plant cells, and in the prokaryotic cells, which are plant cells. The cytoplasm in animal cells is much larger than that found in the plant cell. The fluid of the cytoplasm is a thick soup of proteins, carbohydrates, salts, sugars, lipids, nucleotides, and amino acids. Bacterial cytoplasm contains ribonucleic acid (RNA), on which proteins are sythesized. Cytoplasm has three main functions, energy, storage, and manufacturing. It contains other organelles which store and produce energy. The cytoplasm is also the storage place within the cell.
Other Related Organelles
The cytoplasm contains everything within the cell, except the nucleus. Within the eukaryotic cells, the animal cells, are other organelles. The cytoskeleton gives organization and shape to the cytoplasm. It is a network of fibers of proteins, which is connected to most organelles within the cytoplasm. The three types of proteins which make up the cytoskeleton are: microtubles, intermediate filaments, and microfilaments. The microfilaments are twisted double strands, which functions are; muscle contraction and changes in cell shape. The intermediate filaments consist of eight subunits, which are maintenance of cell shape. The microtubules are tubes consisting of spiraling two-part protein subunits, whose function is the movement of chromosomes during cell division.
Bibliography
1- Audesirk, Teresa and Audesirk, Gerald: Biology: life on Earth, 5th ed., 1999
2- http://www.dcn.davis.ca.us/~carl/cytoplasm.htm
3- http://www.flg.tum.de/pbpz/mm/mt/cytoplasm.htm
4- http://www.sciencenet.org.uk/database/Biology/Cell_Biology/b00300b.htmlb00300b.html
MITOCHONDRIA
In order to understand the mechanism by which the energy released during respiration is conserved as ATP, it is necessary to appreciate the structural features of mitochondria. These are organelles in animal and plant cells in which oxidative phosphorylation takes place. There are many mitochondria in animal tissues; for example, in heart and skeletal muscle, which require large amounts of energy for mechanical work, in the pancreas, where there is biosynthesis, and in the kidney, where the process of excretion begins. Mitochondria have an outer membrane, which allows the passage of most small molecules and ions, and a highly folded inner membrane (cristae), which does not even allow the passage of small ions and so maintains a closed space within the cell. The electron-transferring molecules of the respiratory chain and the enzymes responsible for ATP synthesis are located in and on this inner membrane, while the space inside (matrix) contains the enzymes of the TCA cycle. The enzyme systems primarily responsible for the release and subsequent oxidation of reducing equivalents are thus closely related so that the reduced coenzymes formed during catabolism (NADH and FADH) are available as substrates for respiration.
The Term Paper on The Different Types of Cells
There are three major parts of a cell-- the nucleus, cytoplasm, and cell membrane, if these are stained appropriately, they can be easily seen under a light microscope. The nucleus (in many cell types) is the innermost and is enclosed by a thin membrane. The nucleus contains the genetic material which directs the cells function. The cytoplasm includes specialized structures called cytoplasmic ...
CHROMOSOMES
Human Chromosomes
Legend:
Representation of the 23 paired chromosomes of the human male.
Chromosome: a very long DNA molecule and associated proteins, that carry portions of the hereditary information of an organism.
a. Structure of a chromosome (Typical metaphase chromosome):
A chromosome is formed from a single DNA molecule that contains many genes. A chromosomal DNA molecule contains three specific nucleotide sequences which are required for replication: a DNA replication origin; a centromere to attach the DNA to the mitotic spindle.; a telomere located at each end of the linear chromosome.
The DNA molecule is highly condensed. The human DNA helix occupy too much space in the cell. Small proteins are responsible for packing the DNA into units called nucleosomes.
b. Stained chromosomes:
Chromosomes are stained with A-T (G bands) and G-C (R bands) base pair specific dyes.
When they are stained, the mitotic chromosomes have a banded structure that unambiguously identifies each chromosome of a karyotype. Each band contains millions of DNA nucleotide pairs which do not correspond to any functional structure.
Adapted from K.F. Jorgenson, J.H. van de Sande, and C.C. Lin, Chromosoma 68:287-302, 1978.
c. Karyotype of a male:
The human haploid genome contains 3,000,000,000 DNA nucleotide pairs, divided among twenty two (22) pairs of autosomes and one pair of sex chromosomes.