LG 1- Cell Structure and Function

Things Common to All Cells Genetic Material – Cytoplasm – Plasma Membrane –

Cell Types Prokaryotes – Eukaryotes –

The Nucleus – The Endomembrane Systems – The Golgi Complex – Lysosomes and Peroxisomes – Mitochondria – The Cytoskeleton –The Plant Cell

Chloroplasts – Other Plastids – Central Vacuoles – Cell Walls –

Unit IVCells

Learning Goal 1Examine the structures found in cells

and how they function to maintain homeostasis.

Things Common to All CellsGenetic Material

All cells have a central region that contains DNA molecules.

CytoplasmAll the parts of a cell that surround the central region comprise the cytoplasm.This consists of cytosol, a water solution containing ions and various organic molecules.It also contains organelles, little organs necessary for important cell functions

Cell MembraneThe cytoplasm is surrounded by a cell or plasma membrane.

Cell Types

• Prokaryotes

Make up the two kingdoms of bacteria

Have cell walls that surround the plasma membrane, producing a capsule for protection of the cell.

DNA consists of a single circular molecule called a prokaryotic chromosome.

• Contain structures called ribosomes that are used to assemble proteins for the cell.

• Many prokaryotes have flagella (singular flagellum). This is a tail-like structure that helps bacterial cells to move around.

Eukaryotic Cells

• Organisms from all of the other kingdoms consist of eukaryotic cells. (Protists, Fungi, Plants, and Animals).

• Genetic material is surrounded by a true membrane enclosed nucleus.

• The cytoplasm contains a system of membranous organelles that carry out major cell functions.

The Nucleus

• The nucleus is separated from the cytoplasm by the nuclear envelope which consists of two membranes separated by a narrow space.

• Nuclear pores form openings through both membranes to allow the passage of substances.

• The liquid inside the nucleus is called nucleoplasm.

• The nucleus is filled with chromatin, a combination of DNA and proteins.

• The hereditary information of a eukaryote is distributed among several to many linear DNA molecules in the nucleus. Each of these is called a chromosome.

• The nucleus also contains a structure called the nucleolus.

• These structures play a role in the production on ribosomes.

The Endomembrane System

• Endoplasmic Reticulum

This is an extensive interconnected network of membranous channels and vesicles.

Vesicles, are small membrane-bound compartments that transfer substance between part of the system.

• There are two types of endoplasmic reticulum (ER).

• Rough ER has ribosomes that stud its surface.

• The proteins made on these ribosomes are finished into their final form in the lumen (space) within the ER.

• Smooth ERThere are no ribosomes on these membranes.The smooth ER has various functions in the cytoplasm including synthesis of lipids that become part of the cell membranes. In some cells, such as those of the liver, smooth ER membranes contain enzymes that convert drugs, poisons, and toxic by-products of cellular metabolism into substances that can be tolerated or more easily removed from the body.

• Golgi ComplexThis is a stack of flattened, membranous sacs without attached ribosomes.Further chemical modifications of proteins occur here and are then sorted into vesicles that pinch off from the margins of Golgi sacs.

• Proteins secreted from the cell are transported to the plasma membrane by secretory vesicles which release their contents to the exterior by exocytosis.In this process a secretory vesicle fuses with the plasma membrane and spills the vesicle contents to the outside.Vesicles may form by the reverse process, called endocytosis which brings molecules into the cell from the exterior.

• LysosomesMembrane-bound vesicles that contain hydrolytic enzymes for digestion of many complex molecules.They are the recyclers of the cell.They digest food molecules entering the cell by endocytosis.In a process called autophagy they digest organelles that are not functioning correctly.

Peroxisomes produce hydrogen peroxide as a by-product of break down reactions. This toxic substance is then converted to water and oxygen by the enzyme catalase.

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Mitochondria

• These organelles are known as the “powerhouses” of the cell.

• This is where cellular respiration occurs. In this process energy-rich molecules such as sugars, fats, and other fuels are broken down to water and carbon dioxide by reactions that release energy.

• The mitochondria consist of an outer mitochondrial membrane which is a smooth outer covering.

• An inner membrane is expanded by folds called cristae and surrounds the inner compartment called the mitochondrial matrix.

• The high-energy molecule ATP is produced in the cristae and matrix.

• Mitochondria also contain DNA and ribosomes that resemble those structures in bacteria.

• These and other similarities suggest that mitochondria originated from ancient bacteria that became permanent residents of the cytoplasm during the evolution of eukaryotic cells.

The Cytoskeleton

• This is an interconnected system of protein fibers and tubes that extends throughout the cytoplasm.

• It reinforces the plasma membrane and functions in movement of structures within the cell and of the cell as a whole.

• It is made up of microtubules, intermediate filaments, and microfilaments.

Plant Cells• Chloroplasts

These are the organelles in plant cells that are the site of photosynthesis.They are composed of on outer boundary membrane and an inner boundary membrane. Within these membranes is an inner compartment called the stroma, Within the stroma are flattened closed sacs called thylakoids. Stacks of these sacs are called grana.The thylakoid membranes contain molecules that absorb light energy and convert it to chemical energy. The primary molecule is chlorophyll.

• Other PlastidsBesides chloroplasts there are other organelles known as plastids.Amyloplasts are colorless plastids that store starch, a product of photosythesis.Chromoplasts contain red and yellow pigments and are responsible for the colors of ripening fruits or autumn leaves.Chloroplasts also contain DNA and ribosomes that resemble those of certain photosynthetic bacteria. Like mitochondria they are believed to have originated from ancient prokaryotes.

• Central VacuolesPlant cells contain a central vacuole that are large vesicles that make up 90% or more of the cell’s volume. The membrane that surrounds the central vacuole is called the tonoplast. It moves substances into and out of the central vacuole.Central vacuoles store water and other essential substances.

• Cell Walls

Plant cells have cell walls that surround the plasma membrane.

It is composed of cellulose a complex carbohydrate.

LG 1 Vocab Words

• Cell Commonalities• Prokaryotic vs Eukaryotic Cells• Nucleus• Endomembrane System• Mitochondria• Lysosomes• Cytoskeleton• Chloroplasts• Central Vacuole• Cell Wall