Ultrastructure of Cells Flashcards
What is ultrastructure?
Features that can be seen using an electron microscope
What does metabolism involve?
Vital chemical reaction requiring enzymes and specific conditions - synthesis and breakdown of molecules and the reactions take place in the cytoplasm
What is cytoplasm made up of?
Cytosol - water, salts, organic molecules
How is cytoplasm separated from external environment?
By a cell surface membrane and in eukaryotic cells the cytoplasm is divided into different membrane bound compartments known as organelles that have a variety of functions
Function of membranes?
They are selectively permeable and control the movement of substances into and out of the cells and organelles - effective barriers which control which substances enter and exit cells ; THEY ARE FRAGILE
What does the nucleus contain?
Coded genetic information in the form of DNA molecules - which directs the synthesis of all proteins required by the cell and thus controls all metabolic activities in the cell as many of the proteins are the enzymes necessary for metabolism to take place
Describe the membrane of the nucleus
A double membrane called a nuclear envelope which protects it from damage in the cytoplasm - nuclear envelope contains nuclear pores that allow molecules to move into and out of the nucleus (DNA too large to leave via pores therefore transcribed into mRNA which are then exported)
How is the DNA arranged as in the nucleus?
It associates with proteins called histones to form a complex called chromatin - this coils and condenses to form chromosomes which only become visible when cells prepare to divide (spindle fibres - centrioles mitosis)
What is the nucleoli?
It is within the nucleus and is responsible for producing ribosomes - composed of proteins and RNA ; RNA is used to produce ribosomal RNA which combines with proteins to form the necessary ribosomes for protein synthesis
Function of mitochondria
They are the site of the final stages of cellular respiration where the energy stored in bonds of complex organic molecules is made available to use by the production of ATP - number of mitochondria in the cell reflects the amount of energy it uses therefore very active cells usually have a lot of mitochondria
Structure of mitochondria
Double membrane - inner membrane is highly folded to form cristae structures and the fluid interior is called the matrix
Cristae
INNER MEMBRANE of mitochondria which is highly folded - Membrane forming cristae contain enzymes used in aerobic respiration
Mitochondrial DNA?
Mitochondria contain mtDNA (small amount of DNA) which allows them to produce their own enzymes and reproduce themselves
What are vesicles?
Vesicles are membranous sacs (with fluid inside) that have storage and transport roles - THEY CONSIST OF A SINGLE MEMBRANE (transport materials inside the cell)
What are lysosomes?
Specialised forms of vesicles that contain hydrolytic enzymes that are responsible for breaking down waste material in cells including old organelles ; they play an important role in the immune system as they are responsible for breaking down pathogens ingested by phagocytic cells - PLAY AN IMPORTANT ROLE IN APOPTOSIS (programmed cell death by excessive production of lysosomes)
What are hydrolytic enzymes?
They help in catalysing hydrolysis - use water to break chemical bonds (larger molecules into smaller molecules) - break down old organelles and are responsible for breaking down pathogens (phagocytosis) - play a big role in apoptosis
What is phagocytosis?
Process by which a cell uses it’s membrane to engulf a large particle (including pathogens)
Function of cytoskeleton
Network of fibres essential for shape and stability of a cell - organelles are held in place and it is responsible for cell movement/movement of organelles within cells
3 components of cytoskeleton
Microfilaments
Microtubules
Intermediate fibres
What are microfilaments?
Contractile fibres made of the protein actin - responsible for cell movement and cell contraction during cytokinesis (pinching together during mitosis)
What are microtubules?
Globular tubulin proteins polymerise to form tubes that are used to form a scaffold structure that determines the shape of the cell - act as tracks for the movement of organelles around the cell (including vesicles)
What are spindle fibres made of?
They have a role in physical segregation of chromosomes in cell division - they are composed of microtubules
What are intermediate fibres?
They give mechanical strength to cells and help maintain their integrity
What are centrioles?
A component of the cytoskeleton present in most eukaryotic cells with the exception of flowering plants and most fungi - they are composed of microtubules