A2.2 cell structure Flashcards
prokaryotic cells
- small
- unicellular
- simpler than eukaryotes
- no nucleus (instead nucleoid region with naked loop of DNA)
classifying bacteria: gram positive vs. gram negative bacteria
bacteria classified by their ability to retain dye known as “crystal violet”
- gram positive bacteria e.g bacillus and staphylococcus: when cell wall is exposed to crystal violet, take on a violet/blue appearance
- gram negative: extra outer membrane so that when exposed to crystal violet, do not appear violet/blue under microscope as they do not retain “crystal violet”
structure of prokaryotic cells
- nucleoid region
- pili
- flagella
- cytoplasm
- cell wall
- plasma membrane
- ribosomes (70s)
sometimes has a capsule
nucleoid region in prokaryotes
structure: naked loop of DNA, contains single strand of long, continuous thread of DNA, non-compartmentalised
function: cell control and reproduction
pili and flagella in prokaryotes
pili structure: hair-like growths on the outside of the cell wall
pili function: main role is conjugation, transfer of plasmid from one bacteria to another, attaches bacterium to other cells
flagella structure: long tail-like structure anchored to cell wall and plasma membrane
flagella function: allows for movement of bacterium
cytoplasm in prokaryotes
structure: made of cytosol (water with dissolved substances e.g ions)
function: where all cellular processes take place because there is no compartmentalisation
cell wall in prokaryotes
structure: made of peptidoglycan
function: protects and maintains shape of cell and prevents it from rupturing due to changes in water pressure, internal pressure being greater than external pressure
plasma membrane in prokaryotes
structure: two layers of lipids creating bilayer, studded with proteins involved with cell recognition, communication and transport
function: surrounds and encloses cell contents, controls interactions between cell contents and exterior. plays a role in binary fission
ribosomes in prokaryotes
structure: 70s ribosomes
function: site of protein synthesis (translation)
capsule in prokaryotes
structure: some bacteria have a capsule. it is an extra layer of a type of polysaccharide outside the cell wall
function: makes it possible for bacteria to adhere to structures e.g teeth, skin, food. prevents cell from dehydration and attack of immune system cells e.g antibiotics
plasmids in prokaryotes
structure: some bacteria contain plasmids. small, circular, DNA molecules. independent to the main bacterial chromosome and can replicate independently.
function: not required by cell under normal conditions, but can help cell adapt to unusual circumstances
binary fission
type of asexual reproduction
- DNA is replicated semi-conservatively
- two DNA loops attach to opposite sides of membrane
- membrane elongates and pinches off (cytokinesis) forming two separate cells
- two genetically identical daughter cells are produced
structure of eukaryotic cells
- plasma membrane
- cell wall (plants only)
- nucleus
- membrane riboses
- endoplasmic reticulum: smooth and rough
- golgi apparatus
- lysosomes
- centrosomes
- vacuole
- chloroplasts (plants only)
- cytoskeleton
- mitochondria
cytoplasm in eukaryotes
compartmentalized, made up of cytosol and contains cytoskeleton which prokaryotes do not have
cytoskeleton in eukaryotes
network of small fibres and roots:
- actin filaments
- intermediate filaments
- microtubules
made of protein and functions include:
- maintaining cell of shape
- aiding cellular movement
- anchoring some organelles
endoplasmic reticulum in eukaryotes
extensive network of tubules that extends almost everywhere in the cell, main function is the transportation of materials throughout internal region of cell
smooth ER: no ribosomes, many enzymes on external surface: produces membrane phospholipids and cellular lipids, as well as sex hormones e.g testosterone
rough ER: ribosomes on external surface which are involved in protein synthesis so ER engages in protein development and transport
membrane riboses in eukaryotes
80s ribosomes (larger than prokaryotic) conduct protein synthesis
lysosomes
intracellular digestive centres that come from the golgi apparatus. they are vesicles bounded by a single membrane filled with hydrolytic enzymes that catalyse the breakdown of proteins, nucleic acids, lipids, and carbohydrates. they also breakdown the materials from phagocytosis (a form of endocytosis)
lysosomes have an acidic environment which is necessary for these hydrolytic reactions
golgi apparatus
consists of flattened sacs called cisternae which are stacked. Involved in the transportation, modification and distribution of materials synthesised in the cell Two sides: “cis” side which is close to the rER and receives vesicles from the ER which then pass through the cisternae and come out of the “trans” side with modified materials, e.g lysosomes.
mitochondria
have their own circular chromosomes of DNA and 70s ribosomes (like prokaryotes). Have double membrane: outer membrane is smooth while the inner membrane is folded into cristae with an area between known as the inner membrane space. the inner membrane contains a semi-fluid substance known as the matrix.
cristae give the mitochondria a large surface area where chemical reactions e.g the production of the usable cellular energy adenosine triphosphate (ATP) occur.
nucleus
bordered by a double membrane known as the nuclear envelope to isolate the DNA from other potentially interfering chemical reactions. Not totally isolated, has nuclear pores for communication with cytoplasm. Inside the envelope is the DNA in the form of chromatin
chloroplasts
only in algae and plant cells. double membrane, own circular DNA and 70s ribosomes (like prokaryotes and mitochondria). other internal structures include: stroma, fluid (like cytoplasm) with enzymes and chemicals necessary for photosynthesis, grana made up of stacked thylakoids which are flattened membrane stacks with components necessary for the absorption of light.
centrosome
in animal cells they consist of a pair centrioles which are responsible for the assembly of microtubules (important for maintaining shape of cell, movement, and cell division). fungi and plants do not have centrioles, instead centrosome-like structures that produce microtubules.
centrosomes located close to nucleus and centrioles sometimes produce basal bodies located near pili and flagella which direct the assembly of microtubules.
vacuoles
storage organelles formed from golgi apparatus. small in animal cells but large in plant cells. store food (to provide nutrition for cell), metabolic waste (to remove from cell), and water (to provide rigidity to plant cells).
