1.4 Cells

Prokaryotic cells

An example would be bacteria

CONTAINS NO:

• Nuclei

• Mitochondria

• Endoplasmic reticulum

CONTAINS:

• Naked, circular DNA

• Small ribosomes

• Sometimes plasmids

• Cell wall

• Capsule made of slime

Eukaryotic cells

CONTAINS:

• Membrane bound nucleus

• Chromosomes (helical DNA with a histone protein coat)

• Mitochondria

• Endoplasmic reticulum

• Ribosomes

• Golgi apparatus

• Vesicles

• Lysosomes

• Microtubules

Molecules in a Cell Membrame

• Phospholipid bilayer

• Proteins

• Glycocalyx

• Glycoproteins

• Glycolipids

• Cholesterol (in animals)

• Receptors

• Enzymes

• Antigens

Phospholipid bilayer

Makes up cell surface membrane

• Hydrophillic head

• Hydrophobic tail

In a cell surface membrane, there’s water on both sides. Forcing the phospholipids to form a bilayer

Functions of phosphlipid bilayers

• Allow lipid soluble substances to enter kr leave the cell

• Prevent water soluble substances entering & leaving the cell

• Make the membrane flexible

Proteins & cell membranes

Extrinsic protein: On surface of phospholipid bilayer

Intrinsic protein: embedded into the membrane

Functions of proteins in cell membranes

• Structural support & stability to the cell

• Acts as a channel for movement of water soluble molecules across the membrane. Protein creates a hydrophilic channel so polar molecules can bypass the hydrophobic centre of the membrane

• Allow active transport

• Form recognition sites for identification of cells

• Helps cells stick together

• Act as receptors

• Act as enzymes

Glycocalyx

Contains polysaccharides bound to glycoproteins or glycolipids

• Acts as a barrier for a cell from its surroundings- providing protection

Cholesterol

Lies between phospholipid tails.

Provides stability by restricting sideways movement of phospholipids at high temps.

At low temps cholesterol helps stop adjacent phospholipid molecules sticking together

Function of Emzymes in Cell Membranes

Membrane provides attached enzymes with more stability

Cell Recognition & Cell Receptors

Glycocalyx allows cells to recognise each other & group to form tissues

Glycoprotein receptors & signalling molecules fit together because they have complementary shape

What is a cell membrane?

Structures surrounding cells and contributing to their internal structures

Defines the boundaries of organelles within the cytoplasm

Components of Eukaryotic (animal) cells

• Nucleus

• Endoplasmic reticulum

• Ribosomes

• Golgi apparatus

• Lysosomes

• Mitochondria

• Microtubules

Components of the Nucleus

Contains DNA & histones in the form of chromosomes

• Nucleolus- dark staining area where DNA codes for ribosomal RNA

• Nuclear envelope- A perforated double membrane, separating contents of the nucleus from the cytoplasm. Also provides structure to nucleus

• Nuclear pore- allows molecules to enter/leave the nucleus

Outer membrane of the envelope is encrusted with ribosomes & is the site of origin of rough Endoplasmic reticulum

What is the function of the nucleus?

Protein synthesis

Carries the code for all the proteins a cell needs to make

Endoplasmic Reticulum

Rough Endoplasmic Reticulum has RIBOSOMES on the outside - provides scaffolding for ribosomes to make protein & the e.r. acts as a distribution network for the proteins- common in cells making a lot of protein

Smooth Endoplasmic Reticulum does NOT have ribosomes attached - synthesis of cholesterol, metabolises lipids & distributes them

Ribosomes

• Sites of protein synthesis

• Found free in cytoplasm or attached to r.e.r.

• Made from protein & ribosomal DNA

Golgi apparatus

Series of cisternae lined by a membrane

Has vesicles from ER joining it

Mitochondria

• Enclosed in a double membrane

• Matrix- thick juice filling the mitochondria

• The inner membrane is folded into cristae which project into the matrix - giving the inner membrane greater SA. Thus increasing number of enzymes embedded in membrane

Lysosomes

• Vesicles produced by Golgi that have hydrolytic enzymes