Cell structure Flashcards
eukaryotic cells
-larger than prokaryotic cells
-DNA contained in a nucleus
- most eukaryotic cells are part of complex multicellular organisms containing a range of specialised cells to perform a variety of functions
-specialized cells with similar structures and functions are organised into tissues
-animals, plants and fungi are all eukaryotic organisms.
organisms inside a eukaryotic cell
-cell surface membrane
-nucleus
-mitochondria
-chloroplasts
-golgi apparatus and golgi vesicles
-lysosomes
-ribosomes
-RER (rough endoplasmic reticulum)
-SER ( smooth endoplasmic reticulum)
-cell wall
-cell vacuole
cell surface membrane
-found in all cells
-phospholipid bilyaer- molecules embedded within and attached on the outside (proteins carbohydrates, cholesterol)
function - cell surface membrane
controls the entrance and exit of molecules
nucleus
-nuclear envelope- double membrane
-nuclear pores
-nucleoplasm- granular jelly-like material
-chromosomes- protein bound linear DNA
-nucleolus- smaller sphere in the nucleoplasm which is the site of rRNA production and ribosome synthesis
function of the nucleus
-site of DNA replication and transcription (making mRNA)
-contains the genetic code for each cell.
mitochondria
-double membrane
-an inner membrane called the cristae
-the fluid centre called the mitochondrial matrix
-contains 70s ribosomes and circular DNA
mitochondria function
site of aerobic respiration and ATP production
chloroplasts
-surrounded by a double membrane
-contains thylakoids (folded membranes embedded with pigment)
-the fluid filled stroma contains enzymes for photosynthesis
-found in plants
-contains 70s ribosomes
-contains 70s ribosomes and circular DNA
chloroplast function
site of photosynthesis
golgi apparatus and vesicles
folded membranes making cristernae
-secretory vesicles pinch off from the cisternae
function of golgi apparatus and vesicles
-add carbohydrates to proteins to form glycoproteins
-produce secretory enzymes
-secrete carbohydrates
Transport store and modify lipids from lysosomes
molecules are labelled to reach their destination
-finished products are transported to the cell surface in golgi vesicles where they fuse with the membrane and the contents are released via exocytosis.
lysosomes
Bags of digestive enzymes- can contain 50 different enzymes
function of lysosomes
-hydrolyse pathogens in phagocytosis
-completely break down dead cells (autolysis)
-exocytosis-release enzymes outside of the cell to destroy material
-digest worn-out organelles for reuse of materials
ribosome
-small granuels made up of two subunits of protein and rRNA
-80s large ribosomes found in eukaryotic cells
-70s smaller ribosomes found in prokaryotic cells
function of ribosome
the site of protein synthesis
RER - rough endoplasmic reticulum
- have ribosomes on the cisternae
-both rer and ser have folded membranes called cisternae
function of the RER
protein synthesis
smooth endoplasmic reticulum
has ( along with RER ) has folded membranes called cristernae
function of the SER
synthesises and stores lipids and carbohydrates
cell wall
-in plants and fungal cells
-in plants - made of microfibrils of the cellulose polymer
-fungi- made of chitin, a nitrogen-containing polysaccharide
function of the cell wall
provides structural strength to the cell
cell vacuole
filled with fluid surrounded by a single membrane called tonoplast
function of cell vacuole
-makes cell turgid and therefore provides support
-temporary store of sugars and amino acids
-the pigments are responsible for coloured petals which attract pollinators
prokaryotic cells
- smaller than eukaryotic cells
-no membrane bound organelles
-smaller ribosomes (70s)
-no nucleus
-a cell wall made of murein
bacteria as a prokaryotic cell
-bacteria still contains DNA, but it is not stored in a nucleus ( free floating DNA) instead DNA is found as a single circular molecule in the cytoplasm and is not associated with the histone proteins
-prokaryotic cells do have cell walls, but they do not contain cellulose or chitin, instead they are made of a glycoprotein called murein
three additional features of bacteria
-contain plasmids, which are rings of DNA containing genes linked to survival such as antibiotic resisitance
-some have a capsule surrounding their cell wall, which provides protection from other cells and helps bacteria aggluntinate (stick together)
-some have flagella which are used for locomotion (the movements of objects from one place to another)
viruses
-non living and cellular
-even smaller than bacteria and only contain genetic material, a capsid and attachment proteins
e.g HIV is a virus
methods of studying cells that allow us to know the internal structure of cells
-microscopes
-cell fractionation
-ultracentrifugation
what are the three key types of microscopes
-optical microscopes
-transmission electron microscopes
-scanning electron microscopes
what is magnification
how many times larger the image is compared to the object
what is resolution
the minimum distance between two objects in which they can still be viewed as seperate
how the resolution is determined
-optical microscope
the wavelength of light
how the resolution is determined-
-electron microscope
wavelength of the beam of electrons
optical (light) microscope
- a beam of light is condensed to create the image
-A glass lens is used to condense the beam of light
-poorer resolution due to the light having a longer wavelength
-lower magnification
-coloured images
-can view living samples
small organelles in a cell are not visible using an optical microscope, but living samples can be examined and a coloured image is obtained
electron microscope ( scanning or transmission)
- a beam of electrons is condensed to create an image
-electromagnets are used to condense the beam
-higher resolving power as electrons have a shorter wavelength
-higher magnification
-black and white images
-the sample must be in a vacuum, and therefore non-living
electrons are absorbed by air, which is why samples must be in a vacuum. the image remains in black and white although the samples are stained
Transmission electron microscopes
-extremely thin specimens are stained and placed in a vacuum
- an electron gun produces a beam of electrons that passes through the specimen
-some parts absorb the electrons and appear dark
-the image produced is 2D and shows detailed images of the internal structure of cells
scanning electron microscopes
-specimens do not need to be thin, as the electrons are not transmitted through, instead the electrons are beamed onto the surface and the electrons are scattered in different ways depending on the contours
-this produces a 3D image
how to calculate magnification
image size = actual size x magnification
I=AM
eyepiece graticule
-the scale on the glass disc inside optical microscopes
-can be used to measure the size of objects you are viewing under the microscope
- however when you change the objective lens, and therefore the magnification, you have to calibrate the eyepiece to work out what the distance is between each division at that magnification
what is used to calibrate the eyepiece lens
a stage micrometer
-this is a glass slide with a scale on it which you can place on the stage
-the scale on the stage micrometer is typically 2mm long and the sub-divisions are 10 um apart
calibration steps
- line up the stage micrometer and the eye piece graticule whilst looking through the eyepiece
2.count how many divisions on the eyepiece graticule fit into one division on the micrometer scale
e.g in this example 20 divisions of the eyepiece graticule fit into 10 divisions of the micrometer, meaning two divisions fit into 1 division of the micrometer
- each division on the micrometer is 10 um, so this can be used to calculate what one division on the eyepiece graticule is at that current magnification
now that the graticule is calibrated you can measure the size of cells or organelles
cell fractionation
cells are broken down so that the organelles are free to be seperated. this is done using a homogeniser (blender)
conditions during homogenisation
- kept in a cold solution- to reduce enzyme activity to prevent the breakdown of cell components
-solution must be isotonic to prevent any movements of water by osmosis which could result in organelles shrivelling or bursting
-solution must be buffered to resist pH changes. This is to prevent damage to organelles and enzymes. once the cell has been broken open the solution must be filtered to remove larger pieces of debris.
