1.2 ULTRASTRUCTURE OF CELLS Flashcards
Prokaryotic cells
The first organisms to evolve on Earth and have a simple cell structure
DO NOT have a nucleus
Small in size and are found almost everywhere
Ex. soil, water, skin, intestines, pools, volcanic areas
Archaebacteria (prokaryote)
Found in extreme environments like high temperatures, salt concentrations or pH
Eubacteria (prokaryote)
Traditional bacteria including most known pathogenic forms
Cytoplasm
Internal fluid component of the cell
Nucleoid
Region of the cytoplasm where the DNA is located (DNA strand is circular and called a genophore)
Plasmids
Autonomous circular DNA molecules that may be transferred between bacteria (horizontal gene transfer)
Ribosomes
the sites of protein synthesis
(prokaryotic ribosome = 70S) (smaller than eukaryotes)
Cell membrane
Semi-permeable and selective barrier surrounding the cell
Cell wall
Extracellular structure that encloses the cell, protecting it and
helping to maintain its shape. Prevents the cell from bursting
in hypotonic media
Pili
Hair-like extensions that enable adherence to surfaces (attachment pili)
Flagella
whip-like structure that is responsible for locomotion
Binary fission
a form of asexual reproduction used by prokaryotic cells
Steps of Binary Fission
- The single circular chromosome is replicated
- The two copies of the chromosome move to opposite ends of the cell
- Division of the cytoplasm of the cell - The membrane pinches off (cytokinesis), forming two cells
- Each of the daughter cells contains one copy of the chromosome so they are genetically identical
Eukaryotic cells structure
A more complex structure and are believed to have evolved from prokaryotic cells via endosymbiosis
Eukaryotic cells are compartmentalised by membrane-bound structures (organelles) that perform specific roles
Nucleus (eukaryotic)
double membrane and has pores
contains chromosomes
it is where DNA is replicated and transcribed to form mRNA
this is exported via the nuclear pores to the cytoplasm
Rough endoplasmic reticulum
consists of flattened membrane sacs called cisternae
Attached to the outside of the cisternae, ribosomes (80s)
Main function: synthesise protein for secretion from the cell
synthesised protein is carried in vesicle to the golgi apparatus
Golgi apparatus
consist of flattenend membrane sacs called cisternae, however they are shorter and curved and dont have ribosomes attached and have many vesicles nearby
Main function: processes proteins brought form rER
the proteins are carried to the plasma membrane for secretion
Lysosomes
spherical with a single membrane
formed from golgi vesicles
they contain high concentrations of protein
They contain digestive enzymes used to break down ingesting food in vesicles
Mitochondrion
double membrane
inner contains cristae
the fluid inside is matrix
Main function: produce ATP for the cell by aerobic cell respiration
Fat is digested here if it will be used as energy
Microtubules and centrioles
located in cytoplasm
Microtubles main function: moving chromosomes during cell division
Animals contain centrioles: this consits of two groups of 9 triple microtubles
Centrioles form an anchor point for microtubles in cell division
Cilia and Flagella
whip-like structure
they contain a ring of 9 double microtubles and 2 in the middle
Flagella is larger and only one is present
Cilia is smaller and many are present
cilia and flagella can be used for locomotion
CIlia can create a curretn in the fluid next to the cell
Free ribosomes
synthesise protein
constructed in the nucleolus
Chloroplast
double membrane
contains flattened sacs of membrane called thylakoids
produce glucose and other organic compound by photosynthesis
Starch may be present inside
Vacuoles and Vesicles
consist of a single membrane with fluid inside
Main function: absorb foods from outside and digest them in vacuoles
Expels excess of water
vesicles are very small vacuoles used to transport materials inside the cell
Advantages of compermantalised
- Flexibility of changing the numbers and position of organelles within the cell based on the cell’s requirements
- Enzymes and substrates for a particular process can be much more concentrated than if they were spread throughout the cytoplasm.
- Substances that could cause damage to the cell can be kept inside the membrane of an organelle.
- Conditions such as pH can be maintained at an ideal level for a particular process, which may be different to the levels needed for other processes in a cell.
