An Overview of the Cell With a focus on Plant and Animal Cell Structures

An Overview of the Cell

With a focus on Plant and Animal Cell Structures

Types of CellsO There are two categories all cells

can be divided into:O Prokaryotic cells do not have a

membrane-bound nucleus and the genetic material is scattered throughout the rest of the cell. (doesn’t have a true nucleus)

O Eukaryotic cells have a nucleus surrounded by a nuclear membrane to contain all genetic material. (has a true nucleus)

O Cells vary in size, shape and function.

Prokaryotic vs Eukaryotic Cells

The NucleusO Is the cell’s control center and coordinates all cell

activities.O The nucleus contains chromosomes which are

threadlike structures that contain our genetic code. These chromosomes are made of proteins and deoxyribonucleic acids (DNA)O Chromatin: The complex of DNA and proteins that

make up a eukaryotic chromosome. When the cell is not dividing, chromatin exists as a mass of long thin fibres that are not visible with a light microscope.

O Chromosomes: As the cell prepares to divide (reproduce), the stringy, entangled chromatin coils up and becomes thick enough to be seen as separate structures called chromosomes.

The Nucleus (and Rough Endoplamic Reticulum)

The Nuclear Membrane• Separated from the rest of the cytoplasm by a

double membrane. Pores in the nuclear envelope allows RNA and other chemicals to pass through but keeps the DNA inside

NucleolusO A small spherical structure located inside

the nucleus. O It is believed that the nucleolus creates

ribosomal ribonucleic acid (rRNA) which directs the formation of ribosomes.

The Cell MembraneO The cell membrane (plasma

membrane) surrounds the cell, giving it a definite shape and boundary. It is selectively permeable, so it controls what enters and exits the cell.

Cell WallO In many organisms the plasma

membrane is not the outermost boundary.

O In plants, most algae, fungi and bacteria, there is a cell wall that lies outside the plasma membrane.

O In plants it is made of cellulose and has spaces for water, ions and particles to pass through.

O It is NOT selectively permeable but does offer protection and support for the cell.

• Some plant cells have an additional secondary wall with a middle lamella in between that contains a sticky pectin to hold cells together.

The CytoplasmO The cytoplasm is the gel-like substance

inside the cell.O Cytoplasm - 70% water

- 30% proteins, fats, carbohydrates and

other ions.O Composition is always changing due to

osmosis and diffusion.O The cytoplasm houses the working

“organs” of the cell called organelles.

MitochondriaO Mitochondrion (singular) Mitochondria (plural)O Are oval-shaped organelles and are

the “powerhouses” of the cell.O Mitochondria contain their own DNAO They provide the body with needed

energy in a process called cellular respiration.

O Sugar molecules are combined with oxygen to form carbon dioxide and water with a release of energy.

O Energy is not made in the mitochondrion rather the breakdown of glucose sugar releases energy.

O Energy is available for processes such as:O Muscle contractionO Synthesis of new moleculesO Cellular transport

OTwo separate membranes – a smooth outer membrane and a folder inner membrane.

OCristae – fingerlike projections of the folded inner membrane. Each contains special enzymes to help breakdown glucose.

RibosomesO Smallest organelle in the cell.O Site of protein synthesis.O Proteins are the molecules that

makes up cell structure.O Cell growth and reproduction require

constant synthesis of proteins.O In the nucleus, DNA sends

messenger molecule to produce protein in ribosomes of the cell.

O Location: found both scattered throughout the cytoplasm and attached to endoplasmic reticulum.

Endoplasmic reticulumO A series of canals that carry

materials throughout the cytoplasm.

O Composed of parallel membranes.O 2 types:

1. Rough endoplasmic reticulum 2. Smooth endoplasmic reticulum

Rough Endoplasmic Reticulum

O Organelle with a double membrane and ribosomes attached.

O Extends from the nuclear membrane to the cell membrane.

O Transports proteins made by the ribosomes to the Golgi apparatus.

Smooth Endoplasmic Reticulum

O Double membrane bound organelle without ribosomes.

O Also extends throughout the cell.O Produces lipids for the cell.

Golgi ApparatusO Appears like a stack of pancakes.O They are membranous sacs piled on

top of each other.O Function:

O To package , modify and store proteins produced by ribosomes on the rough endoplasmic reticulum.

O To release large molecules (hormones, enzymes) by exocytosis.

O Golgi apparatus migrates towards the plasma membrane where small packets (called vesicles) are released and pass through plasma membrane by exocytosis.

O The golgi apparatus will also form lysosomes

LysosomesO Formed by exocytosis of vesicles

from Golgi apparatus and are smaller than mitochondria.

O They are sac-like structures that contain digestive enzymes to break down large molecules and cell parts within the cytoplasm.

O Only found in animal cells

O Purpose:O The break down cell “food” to use as an

energy source.O As a defense mechanism for the

immune system.O The Immune Response

O Lysosomes destroy harmful substances that find their way into the cell.

O Example: White blood cells phagocytise foreign particles. Lysosomes then release digestive enzymes to destroy the invader.

O Lysosomes are also known as “suicide sacs”.

O Body cells have a certain lifespan after which they die and must be cleaned up. Digestive enzymes in lysosomes clean up cell parts after body cells die.

VacuolesOVacuoles are fluid-filled, membrane-

bound structures that store substances produced by the cell for future use.

OThey are reservoirs for sugars, minerals, proteins, water and wastes.

OGives plant cells physical support. OPlant cells have large, central vacuoles.OAnimal cells have many smaller vacuoles.

CytoskeletonO Microfilaments are

threadlike structures in the cytoplasm that help provide shape & movement.

O Microtubules are tube-like fibres (made of protein) that transport materials through the cytoplasm – also found in flagella & cilia.

Cilia and FlagellaO A flagellum is a whip like tailO that aids in movementO Flagella spin like a propellerO Cilia (cilium)are shorter, hair

like structures that aid in

movement and moving materials.

CentriolesO Composed of nine bundles of three

microtubules.O Found only in animal cells.O Play a key role in cell division.

PlastidsO Plastids are “chemical factories” and

“storehouses” for food and other pigments in plant cells

O Only found in plant cells!O Chloroplasts are plastids that contain the

green pigment chlorophyll that is used for photosynthesis.

O Chromoplasts- store orange and yellow pigments

O Amyloplasts- colourless plastids that store starch

OPlastid structure:O Made of a double membraneO Packets of chlorophyll inside which taps

into the Sun’s energy to make sugar.