Common Parts of Eukaryotic Cells

  1. The plasma membrane (also called the cell membrane )forms a barrier to create an environment inside the cell that is separate from the environment outside the cell. The membrane is a vital border. It controls what enters and what leaves the cell.
  2. The cell membrane is semi-permeable , allowing only select ions and organic molecules to enter and/or leave the cell.
  3. Phospholipid Bilayer: The cell membrane consists of two layers of phospholipidswith embedded proteins which have numerous functions
  1. Cytoplasm refers to all of the cellular material inside the plasma membrane, other than the nucleus. Cytoplasm is made up of a watery substance called cytosol , and contains other cell structures such as ribosomes.
  1. Ribosomes are structures in the cytoplasm where proteins are made.
  1. DNA is a nucleic acid found in cells. It contains the genetic instructions that cells need to make proteins.
  1. Nucleus is the control center of the cell that contains the chromosomes with their genetic material, DNA. The nucleus controls all cellular functions.
  2. Chromosomes are large molecules in the nucleus made up of DNA and protein.
  3. Mitochondria are the factory and storage center for ATP, which is used as energy by the cell in making cellular products and carrying out the functions of the cell.
  4. Endoplasmic reticulum (ER) is an elaborate membrane system throughout the cytoplasm. Portions of ER contain ribosomes on the membrane surface.
  5. Golgi apparatus are the flattened sacs that help sort the proteins synthesized by the rough ER and ribosomes.
  6. Vacuoleis a storage sack filled that contains water and food.

In addition Plant Cellscontain:

  1. CellWall:Toughlayer thatsurroundsplant cells and provides support and structure.
  2. Chloroplast:Organelles foundinplant cells that are responsible forphotosynthesis.

CELLTRANSPORT&.HOMEOSTASIS

The cell membrane regulates what goes in and out of the cell by only allowing certain substances to pass through. Substances can cross the membrane by either passive or active transport.

  • Passive transport includes diffusion and osmosis. In passive transport, molecules move from areas of high concentration to areas of low concentration in order to reach homeostasis.
  • An example of active transport is the sodium-potassium pump, which plays an important role in moving sodium and potassium ions in and out of the cell.

Homeostasisisoneofthe unifyingprinciplesofbiology.Theconcentrationofvarioussubstances,suchassalts and nutrients,needsto bewithinacertainrange inorder for acelltofunctionnormally.Tomaintainthis balance,acell needs to beabletomovesubstancesinand out.

Passive Transportreferstothe movementofsubstances across the membranewithoutany inputofenergyfrom the cell.Three main types ofpassivetransportinclude:

  • Diffusion,where molecules"movedown the concentrationgradient"fromanareaofhigh concentrationto anarea of lowconcentrationuntil equilibriumisreached (the concentration ofmoleculesonbothsidesofthe membraneareequal).
  • Osmosis,aspecialtype ofdiffusionspecificallyreferring tothemovementofwater across acell membrane.

Example: if there is a higher concentration of salt outside a cell than inside it, there is a lower concentration of water outside the cell than inside it. As a result, water inside the cell will diffuse out of the cell. For animal cells, this will cause the cell to shrivel. In plant cells, the cell wall is rigid but the plasma membrane will shrink and pull away from the wall

  • Facilitated diffusion,a type of diffusionassisted by transport proteins.

Active Transport refers to the movement of substances across the membrane that requires an input of energy from the cell. Energy for active transport comes from an energy-carrying molecule called ATP.

Energy is required to move substances against the concentration gradient from areas of low concentration to areas of high concentration (contrary to the natural process of diffusion). Energy is needed to move very large molecules across the membrane. Examples of this is the sodium-potassium pump, endocytosis, and exocytosis.

Cell Division & Cell Cycle

The cell cycle is the life cycle of a cell. A cell spends its life growing, replicating DNA, performing other life functions, and dividing. For eukaryotic cells, the cell cycle consists of two general phases: interphase and the mitotic phase. Cell division is part of the life cycle for almost every cell. It is a more complicated process in eukaryotic than prokaryotic cells. Eukaryotes have multiple chromosomes and many organelles, all of which must be duplicated and separated for the cell to divide.

Chromosomes are coiled structures made of DNA and proteins. Chromosomes are the form of the genetic material of a cell during cell division. During other phases of the cell cycle, DNA is not coiled into chromosomes. Instead, it exists as a grainy material called chromatin.

Chromatids and the Centromere

DNA condenses and coils into the familiar X-shaped form of a chromosome, shown in Figurebelow, only after it has replicated. Because DNA has already replicated, each chromosome actually consists of two identical copies. The two copies are called sister chromatids. They are attached to one another at a region called the centromere.

Chromosomes and Genes

The DNA of a chromosome is encoded with genetic instructions for making proteins. These instructions are organized into units called genes. Most genes contain the instructions for a single protein. There may be hundreds or even thousands of genes on a single chromosome.

Human Chromosomes

Human cells normally have two sets of chromosomes, one set inherited from each parent. There are 23 chromosomes in each set, for a total of 46 chromosomes per cell. Each chromosome in one set is matched by a chromosome of the same type in the other set, so there are actually 23 pairs of chromosomes per cell. Each pair consists of chromosomes of the same size and shape that also contain the same genes. The chromosomes in a pair are known as homologous chromosomes.

Mitosis and Cytokinesis

During mitosis, when the nucleus divides, the two chromatids that make up each chromosome separate from each other and move to opposite poles of the cell.

Mitosis is the phase of the eukaryotic cell cycle that occurs between DNA replication and the formation of two daughter cells.

Mitosis occurs in four phases as shown in the figure. The product of mitosis is two cells each with the same number of chromosomes as the original cell.

Organic Compounds

Our body is made out of four basic classes of organic compounds: carbohydrates, lipids, proteins, and nucleic acids. Each class performs a unique role and is vital for the function of life.

Carbohydrates

• The most common type of organic compound.

• Built of small, repeating simple sugars (monosaccharides) that can bind to make a larger molecule (polysaccharide)

provides energy to cells, stores energy, forms body structures
Lipids
• Made up of fatty acids–either saturated (carbon bonded to as many hydrogen atoms as possible) or unsaturated (some carbon bonded to groups other than hydrogen atoms)
• Lipids include:
• triglycerides: the main form of stored energy in animals
• phospholipids: the major components of cell membranes
• steroids: serve as chemical messengers and have other roles

Proteins

• Made up of amino acids connected with peptide bonds

• There are 20 amino acids, which, like the alphabet, can be arranged in any order and number to form a near-infinite number of polypeptides

• The shape of a protein is important for function. There are four different structures that proteins can form in the body.

Enzymes are proteins that are found in all living organisms. Without enzymes, most chemical reactions within cells would occur so slowly that cells would not be able to work properly. Enzymes function as catalysts.For example, the food that you eat is broken down by digestive enzymes (like how pepsin breaks up proteins in the stomach) into tiny pieces that are small enough to travel through your blood stream and enter cells.

Catalysts accelerate the rate of a chemical reactions without being destroyed or changed. Enzymes are generally named after the substrate affected, and their names usually end in –ase. For example, enzymes that break down proteins are called proteases.

The compounds that enzymes act upon are known a substrates. The substrate can bind to a specific place in the enzyme called the active site. The rate of the reaction between an enzyme and a substrate can be affected by the following different factors such as temperature, pH, or the concentration of the enzyme and the substrate

Nucleic Acids

• Nucleic acids include DNA, which is double-stranded, and RNA, which is single-stranded. Nucleic acids are made up of nucleotides. Nucleotides are made up of:

• sugar

• phosphate group

• nitrogen base

• Chemical bonds between the sugar of one nucleotide and the phosphate group of the next nucleotide hold together the backbone of all nucleic acid molecules.

• There are five different types of nitrogen bases: cytosine, adenine, guanine, and either thymine (present in DNA) or uracil (present in RNA).

• These bases pair up in a specific way, forming complementary base pairs. Adenine bonds only with thymine (uracil in RNA), and cytosine only with guanine.

• Hydrogen bonding between base pairs holds together two strands of nucleic acid, forming the double helix in DNA molecules.