AICE Biology - Organelles

CRYING

Cell Surface Membrane Structure

Cell Surface Membrane Structure

• A very thin membrane, composed of phospholipids and proteins that surrounds ALL Cells

• 7 nm thick & partially permeable

Cell Surface Membrane Functions

• Controls the exchange of materials between the cell and it's outside environment

• Allows other cells to interact with each other

Nucleus Structure

• Largest organelle found in eukaryotic cells (absent in prokaryotic cells) is 5-10 μm in diameter

• Surrounded by a double membrane (Nuclear Envelope)

Nucleus Functions

• Contains the cell's DNA

• Genetic code controls the activities of the cell

• DNA codes (mRNA) for the synthesis of proteins in the cytoplasm

• Production of mRNA

• Contains Nucleolus which manufactures ribosomes

Chromatin

• loosely coiled genetic material that makes up chromosomes, a made of proteins, DNA, and small amounts of RNA

• Coils up and becomes chromosomes during cell division

Nucleolus Structure

• One to several in nucleus, 1-2 μm in diameter

• Non-membrane bound, usually seen as a densely stained body, made of loops of DNA

Nucleolus Function

• Makes ribosomes using the information in its own DNA

• Synthesizes ribosomal rRNA and tRNA

Nuclear Envelope Structure

• Double membrane with pores

• Membranes are close together and surround all of the nucleus

Nuclear Envelope Functions

• Controls the exchange of materials in and out of the nucleus

• Separates DNA/ genetic materials from the rest of the cell

• mRNA through the pores to the cytoplasm, carrying instructions for synthesis of proteins

Cytoplasm

A jellylike fluid made of mostly water inside the cell in which the organelles are suspended.

Ribosomes Structure

• Non-membrane-bound, spherical structures

• Ribosomes are made of protein and ribosomal RNA (rRNA)

• Found in ALL cells -80s ribosomes are larger (25+ nm diameter) -70s ribosomes are smaller (20- nm diameter)

• Found in mitochondria, chloroplast and more

Rough Endoplasmic Reticulum Structure

• Network a flattened sacs (cisternae)

• Continuous with the outer membrane of the nuclear envelope

• Sacs are interconnected

• Covered with ribosomes on its outer surface

Rough Endoplasmic Reticulum Functions

• Provides a large surface area for polypeptide/protein synthesis

• Proteins are often modified

• Transports proteins to Golgi Body

Smooth Endoplasmic Reticulum Structures

• Flattened sacs

• Membranes which surround an enclosed inner cavity

• No ribosomes

Smooth Endoplasmic Reticulum Functions

• Synthesis and transport of lipids

• Lipids like sterol, cholesterol and steroids like estrogens

• Plays a role in the conversion of glycogen to glucose

Golgi Body Structure

• a series of stacked, membrane-bound sacs flattened membrane sacs (not interconnected)

• Swelling at the end of sacs for vesicle formation

• Constantly forming in one, breaking in the other, a "cycle"

Golgi Body Functions

• chemically modifies proteins Example: Sugars can be added to proteins which makes glycoproteins

• Packages proteins for export from the cell by exocytosis

• Packages hydrolytic enzymes that will remain in the cell/makes lysosomes

Golgi Cycle

• Cis face (receiving side) gets transports vesicles from the rough ER

• Turns into cisternae

• The trans face (shipping side) creates secretory vesicle, carrying content to other parts of the cell, usually the surface membrane for secretion

Mitochondria Structure

• around 1 μm in diameter, 10 μm in length

• double membrane bound

• a smoother outer membrane and an inner membrane that is folded in to a number of cristae

• contains circular DNA and 70S ribosomes

Mitochondria Function

• Carries out aerobic respiration

• Makes ATP

• Aerobic respiration releases energy

ATP-ADP Cycle

ATP (3) breaks down into ADP (2), the released molecule is energy for the cell. The ADP is then reused to create more ATP. ATP is used for protein synthesis, active transport, muscle contraction, and DNA replication.

Lysosomes Structure

• Single membrane bound

• Manufactured by the Golgi Body

• Large central vacuole may act as a lysosome in plant cells

Lysosomes Functions (Part 1)

• Contains digestive enzymes which must be kept from the rest of the cell to prevent damage

• Digests unwanted materials and old/worn-out organelles

• Lysosomes contain proteases, lipases, and nucleases which break down proteins, lipids, and nucleic acids respectively. (There are more enzymes in lysosomes)

Lysosomes Functions (Part 2)

• Endocytosis: White blood cells engulf bacteria then lysosomes fuse with endocytic vacuoles formed and release enzymes to digest the contents

• Exocytosis Lysosomal Enzymes may be released for outside the cell for extracellular digestion

• Self-Digestion: If something is wrong with the cell, lysosomes are released to engulf itself (Called Autolysis)

Centrioles Structure

• Two small, non-membrane bound, cylindrical structures made from microtubules

• Two hallow cylinders about 500 nm long

• Found outside the nucleus in animal cells, in a region known as the centrosome

Centrioles Function

• Organizes microtubules to produce the spindle (which divides the chromosomes in a parental cell into two daughter cells) during nuclear division

• Replicate during the S phase of interphase of the cell cycle (before the nucleus divides)

• Plants DO NOT have centrioles

• Needed for the production of Cilia

Microtubules Stucture

• Long, rigid, hallow tubes found in the cytoplasm

• 25 μm in diameter

• Made of a protein called tubulin

Microtubules Structure

• Cell support, determines cell shape, helps in the movement of organelles

• Secretory vesicles and other organelle and cell components can be moved along the surface of the microtubules, forming a transport system

• Microtubules are important for the beating movements of Cilia and Flagella

Organelles bounded by a single membrane

• Lysosomes

• Golgi Body

• Endoplasmic Reticulum

• Vacuoles

Organelles bounded by two membranes (envelope)

• Nucleus

• Mitochondrion

• Chloroplast

Organelles NOT bounded by membranes

• Ribosomes

• Centrioles

• Microtubules

• Nucleolus

Cilia and Flagella Structures (Part 1)

• Whip-like, beating extensions of eukaryotic cells

• Surrounded by an extension of the cell surface membrane

• Flagella are long and are one or two per cell -Cilia is short and often numerous

Cilia and Flagella Structures (Part 2)

• The cylindrical structure inside the cell surface membrane is called the axoneme

• A Cilium is like the long part of Cilia, it has an arrangement of "9+2"

• The base is the basal body, which is identical to the centriole

• Centrioles replicate to create the basal body

• Cilia and Flagella grow from basal bodies

Cilia and Flagella Functions

• Allows locomotion for the cell

• They do this by beating and moving

• More mitochondria are needed to able to move (more energy)

Microvilli (Structure)

• Small, finger-like extensions of a cell surface membrane, typical of certain epithelial cells

Microvilli (Function)

• Increases the surface area of the cell for more efficient absorption or secretion

• Speeds up absorption of nutrients, like water, glucose, etc

Chloroplast (Structure)

• Double-bounded membrane

• Diameter of about 3-10 μm, elongated shape

• Contains a gel fluid called stroma

• Sacs called thylakoids which stack to become granum

• Contains 70S ribosomes & Circular DNA

Chloroplast (Function)

• Carries out photosynthesis

• Creates ATP (does not release energy)

• Light-dependent reaction: light energy is absorbed by chlorophyll (in the thylakoids) and makes ATP

• Light indépendant reaction: Uses ATP to create carbon dioxide into sugars (in the stroma)

Cell Wall Structures

• A thick wall surrounding prokaryote, plant & fungal

• Freely permeable

• Plant cell wall Is made of the carbohydrate cellulose a polymer of Beta glucose joined by 1,4 glycosidic bonds

Cell wall Function

• Supports the cell and its shape

• protects from mechanical damage

• Prevents it from bursting due to osmosis

• Lignification (Wall becomes harder)

• Apoplectic pathway goes through the cell wall (materials can flow through here)

Plasmodesmata Structure

• Pores in plant cell walls, containing fine strands of cytoplasm that link the neighboring cell

• The symplastic pathway goes through these links

• Pores contain ER and are lined with cell surface membrane

Plasmodesmata Function

• Allows the controlled passage of materials from one cell to another, allowing movement for the materials

Vacuoles Structure

• Single membrane-bound sac-like structures

• A large permanent central vacuole is common in plants

• Tonoplasts are the membrane which surrounds the vacuole

Vacuoles Functions

• Storage of biochemicals, pigments, water, and more

• Animals have small temporary vacuoles, such as phagocytic vacuoles

• Supports the cell shape by inflating the cell, known as a turgid cell. A deflected cell is called a flaccid cell.

• Vacuoles contain hydrolase and act as lysosomes

Structures found in a typical bacterium

• Unicellular

• 1-5 µm

• Peptidoglycan cell walls

• Circular DNA

• 70s Ribosomes

• Absence of organelles surrounded by double membrane

Structures sometimes present in a bacterium

• flagellum (locomotion)

• capsule/slime layer wall for extra protection

• infolding of cell surface membrane

• plasmid (small circle of DNA)

• pili (attachment to surfaces/cells or for sexual reproduction)

Prokaryote

An organism whose cells do not contain a nucleus or any other membrane-bound organelles

Bacterial Cell wall

Contains a strengthening material called peptidoglycan, which protects the bacteria and prevents it from bursting

Peptidoglycan

A polysaccharide combined with amino acids; it is also known as murein; it makes the bacterial cell wall more rigid

Endosymbiont Theory

States that the mitochondria and the chloroplast are ancient bacteria which evolved to live in eukaryotic cells

Evidence: Circular DNA, 70s ribosomes, reproduce by diving in two(fission)

Viruses

• Non-cellular structures

• contains a nucleic acid code (RNA/DNA)

• Capsid made of protein

• 20-300 nm