Topic 2 Cell Organelles

Cytoskeleton

Made up of microfillaments (smallest), intermediate fibres, and mircotubules (largest)

Microfilaments (smaller)

Made of actin, which can contract and is therefore vital for intracellular transport and cell movement. Also plays a role in cytokinesis.

Intermediate fibres

Composed of various protein fibres, they strengthen the cell and are useful in cells that undergo a lot of mechanical stress, eg. skin cells.

Microtubules (larger)

Made of tubulin subunits that form polymers that form hollow mircrotubules. Used in movement of organelles and make up the spindle fibres in meiosis and mitosis. They also help to determine the shape of the cell.

Chloroplasts

Cell organelle, found only in plants and algae that is responsible for photosynthesis

Stroma

Alkaline fluid found inside chloroplasts, that is the site of the light independant reactions in photosynthesis (site of Calvin Cycle). It contains starch grains, ribosomes, cpDNA, and the grana.

Chloroplast: Ribosomes

Translate genetic information from cpDNA, to form specific proteins (such as enzymes) needed for photosynthesis.

Thylakoids

Flat, membrane bound sacs where the light dependant reactions of photosynthesis take place. Photosynthetic pigments such as chlorophyll reside in the thylakoid membrane.

Grana

A granum is a stack of thylakoids and they provide a large surface area for light absorbtion for photosynthesis.

Lamella

Channels that connect grana together forming the thylakoid network. Vital to maintain proper spacing between grana to keep the rate of photosynthesis high.

Chloroplast: Outer Membrane

Contains large channel proteins to let small molecules in and out of the chloroplast, and maintains a isolated internal environment, separate from the cytoplasm of the cell. Also provide the chloroplast with structure.

Chloroplast: Inner Membrane

Actively regulates molecules passing between the cytoplasm and the stroma, helps to regulate the internal environment of the chloroplast and is also invovled in the production of lipids and fatty acids needed in the chloroplast.

Starch grains

Way of storing excess glucose from photosynthesis, without disrupting the osmotic balance of the cell.

Chloroplast DNA

Codes for specific proteins needed in the chloroplast, so they can be synthesised independantly from the rest of the cell. (circular and double stranded)

Cytoplasm

Made of cytosol, made up of water, salts and other organic molecules. Contains the cytoskeleton. Site of metabolic reactions in the cell.

Cell surface membrane

Controls substances moving in and out of the cell (selectively permeable), controls the internal cell environment, and has recpetors that work in cell signalling.

Phospholipid bilayer

Hydrophyllic polar heads ace outwards and hydrophobic fatty acid tails face inwards. This creates a barrier that blocks water-soluable and polar substances from entering the cell.

Cholesterol

Regulates the fluidity of the cell surface membrane and provides stability at extreme temperatures.

Intrinsic proteins

Span the width of the plasma membrane and act as channel proteins for active transport and facilitated diffusion.

Extrinsic proteins

Sit on the outside of the cell surface membrane and assist in cell recognition as weel as providing strucural support.

Glycoproteins and glycolipids

Proteins or lipids with attached carbohydrate chains. They act as receptors for cell signalling and hormones, or as antigens for cell recognition.

Mitochondria

Double membrane bound organelles, responsible for aerobic respiration and producing adenosine triphosphate (ATP) in eukaryotic cells.

Mitochondria: Outer membrane

A smooth phospholipid bilayer that separates the organelle from the cytoplasm and contains transport proteins (porins) to regulate the entry and exit of molecules.

Mitochondria: Inner membrane

Impermeable to most small ions. It is folded into structures called cristae, which provide a large surface area.

Mitochondria: Inner membrane space

A narrow fluid-filled space between the outer and inner membranes.

Matrix

An aqueous central compartment enclosed by the inner membrane. It contains soluble enzymes as well as mitochondrial DNA and (70S) ribosomes.

Mitochondrial DNA and Ribosomes

Circular DNA and small ribosomes allow mitochondria to synthesize some of its own respiratory proteins and enzymes independently.

Ribosomes: Structure

Two subunits: large and small, not membrane bound.

Ribosomes: function

Site of translation in protein synthesis.

Ribosomes: location

Some ribosomes float freely in the cytoplasm, and some are found bound the to RER.

Rough endoplasmic reticulum

Has 80S ribosomes bound to its surface and processes, folds and transports proteins.

Smooth endoplasmic reticulum

Responsible for lipid and carbohydrate synthesis and storage.

Endoplasmic reticulum

A network of membranes enclosing flattened sacs called cisternae. It is connected to the outer membrane of the nucleus.

Eukaryotic Flagella

Whip like extensions that protrude from some cell types, used in cell motility, or as sensory organelles.

Cillia: Function

Mobile cilia can beat rhythmically to move substances to moce adjacent to the cell, eg. in the trachea. Stationary cillia on the surface of cells are important in sensory organs such as the nose.

Cillia: Structure

Two central mircotubules surrounded by nince pairs of mircotubules arranged like a wheel. (9+2 arrangement) Pairs of parallel mircrotubules slide over each other cuasing the cilia to move.

Golgi apparatus

Similar in structure to the smooth ER, compact sturcture of cisternae with no ribosomes. It modifies proteins and “packages“ them into vesicles, either secretory vesicles or lysosomes. Has a trans face and a cis face

Centrioles

Part of the cytoskeleton, present in most eukaryotic cells (apart from most fungi and flowering plants). They are made of microtubules, and two associates centrioles form the centrome, which is involved in the assembly + organisation of spindle fibre in cell division. Also help to position cillia and flagella.

Nucleolus

Area within the nucleus responsible for producing ribosomes. Made of proteins and RNA, used to produce rRNA, which is combined with proteins to make ribosomes.

Nucleus

Contains DNA, and controls the metabolic activities of the cell. Has a double membrane called the nuclear envolope in wich the DNA is contained to protect it from damage in the cytoplasm. It has nuclear pores to allow transcribes DNA to leave the nucleus for protein synthesis.

Chromosomes

DNA associates with histones to form chromatin, which coils/condenses to form chromosomes.

Vesicles

Membranous sacs that have storage and transport roles. Consist only of a single membrane with fluid inside.

Lysosomes

Lysosomes are special forms of vesicles that contain hydrolytic enzymes (lysozymes) and are responsible for breaking down waste material such as old oarganelles. They break down pathogens ingested by phagocytes and have a role in programmed cell death (apoptosis).

Cellulose cell wall

Freely permeable so substances can pass in and out of the cell, gives plant cells shape and structure, provides a defence against pathogens.

Vacuoles

Membrane lined sacs containing sap. Plants have large permenant vacuoles. Membrane is called the tonoplast and is selectively permeable. If vacuoles appear in animal cells they are small and transient.

Prokaryotic DNA

One circular chromosome, which is supercoiled to make it very compact.

Prokaryotic Ribosomes

70S not 80S, smaller and dont make as many complex proteins.

Prokaryotic Cell wall

Made of murein (peptidoglycan), a complex polymer of amino acids and sugars.

Prokaryotic Flagella

Thinner than eukaryote’s, do not have the 9+2 arrangment. Energy for rotation comes from chemiosmosis, not ATP. Attached to the plasma membrane of the cell.