Cell structure Lecture 2

A.Cell Membrane a.The cell membrane regulates what enters and leaves the cell and also provides protection and support b.Takes in water and food and eliminates waste c.The membrane is a double-layered sheet called a lipid bi-layer i.Polar heads face outwards and non-polar tails face inwards d.Embedded in the membrane are protein channels/pumps and carbohydrates

B. Cell Wall a.Where is it found? i.Found in almost all prokaryotes ii.Found in plants, fungi, and algae iii.NOT found in animals b.Lies outside of the cell membrane c.Allow for movement of certain molecules i.Water, carbon dioxide, oxygen and some other substances d.The main function of the cell wall is to provide support and protection to the cell e.Cell walls are made of carbohydrates produced by the cell i.Plants use cellulose

C.Nucleus a.Discovered by a botanist named Robert Brown in 1831 b.The nucleus controls most cell processes and contains the hereditary information of DNA c.Consists of 4 parts i.Nucleolus – small densely packed region where ribosomes are created ii.Nuclear Envelope – double membrane layer surrounding the nucleus iii.Nuclear Pores – a perforations within the nuclear membrane iv.Chromatin – this is the granular material within the nucleus 1.Chromosomes – the condensed form of chromatin just before a cell divides

D.Cytoskeleton a.A network of protein filaments that helps the cell keep its shape, also used in many forms of cell movement b.Made up of microtubules and microfilaments i.Microtubule – hollow tubes of protein which also serve as tracks for organelles to move ii.Microfilament – Long thin fibers that function in the movement and support of the cell

E.Organelles a.Ribosomes i.Ribosomes assemble proteins following the coded instructions that come from the nucleus ii.Ribosomes are made of protein and RNA

b.Endoplasmic Reticulum i.The organelle in which components of the cell membrane are assembled and some proteins are modified ii.Smooth ER – contains collections of enzymes that perform specialized tasks, such as the synthesis of lipids iii.Rough ER – the part that is involved in the synthesis of proteins; has ribosomes embedded in the membrane

c.Golgi Apparatus i.Proteins made by the ER move to the Golgi apparatus where enzymes attach carbohydrates and lipids ii.Discovered by Camillo Golgi

d.Lysosomes i.Are small organelles filled with enzymes ii.Main function is to break down lipids, carbohydrates and proteins into particles that can be used by the cells iii.Also helps to break down old organelles, remove debris from the cell

e.Vacuoles i.Storage for the cell 1.Stores materials such as water, salts, proteins and carbohydrates ii.Plants have a single large vacuole iii.Vesicles are the animals cell equivalent to vacuoles

f.Chloroplasts i.Found in photosynthetic organisms ii.Use energy from sunlight to make energy-rich food molecules in a process known as photosynthesis iii.Enclosed by two envelope membranes iv.Contains thylakoids and chlorophyll v.Contains its own DNA

g.Mitochondria i.Releases energy from stored food molecules in a process called cellular respiration ii.Enclosed by two envelope membranes iii.Found in nearly all cells iv.Contains its own DNA

h.Organelle DNA i.Lynn Margulis suggested that mitochondria and chloroplasts were originally prokaryotic organisms that were enveloped by a eukaryotic cell ii.The DNA in mitochondria comes almost exclusively from the mother

F.Movement through the membrane a.Facilitated diffusion i.Molecules such as glucose that cannot cross the cell membrane’s lipid bilayer directly can move through protein channels from an area of high concentration to an area of low concentration with the concentration gradient b.Active transport i.When a molecule has to move against the concentration gradient ii.Uses energy iii.Each pump is used to move a specific molecule across the membrane 1.Example: sodium potassium pump moves sodium out and potassium in iv.Endocytosis 1.The process of taking materials into the cell by means of infolding or pockets of the cell membrane 2.The resulting pocket breaks loose from the outer portion of the membrane creating a vesicle within the cytoplasm 3.Phagocytosis is then used to break up the vesicle and use the molecules inside v.Exocytosis 1.The removal of large amounts of material from a cell 2.The membrane of the vesicle surrounding the material fuses with the cell membrane forcing the contents out of the cell