Cell structure Flashcards
What is the first stage of cell fractionation?
Cells are placed on a cold, buffered solution at the same water potential
What is the supernatant?
Solution formed when denser components form pellets whilst others remain in suspension above
Why do electron microscopes have a higher resolution?
Shorter wavelength
Why can’t living cells be used in an electron microscope?
A near vacuum has to be created so the electrons aren’t absorbed or deflected by air
How are electron beams focused?
Electromagnets
What’s the resolving power of TEM?
0.1nm
What’s the resolving power of SEM?
20nm
What are the main limitations of TEM?
Vacuum so no living specimens
Complex staining but no colour
Extremely thin
May contain artefacts
2D image
What are the limitations of SEM?
All of TEM, but the specimens don’t need to be thin
What does the nucleolus do?
rRNA production- the RNA then creates proteins
Produces ribosomes
In what form does DNA exist inside the nucleus?
Chromatin
What are the holes in the nuclear envelope called?
Pores
What’s the diameter of the nucleus?
10-20 micrometers
What do nuclear pores do and how many are there?
Allow passage of large molecules such as mRNA
3000, 40-100nm
What is the nuclear envelope?
Double membrane, outer is continuous in ER
Controls entry and exit of substances
What’s the shape and size of mitochondrion?
Rod-shaped and 1-10 micrometers in length
What is the cristae?
Inner membrane of mitochondria containing enzymes for respiration
What’s inside the matrix of the mitochondria?
Proteins, lipids, ribosomes and DNA, many of the enzymes for respiration
What are they typical sizes of chloroplasts?
Disc-shaped 2-10micrometers in length and 1 micrometer in diameter
What’s the chloroplast envelope?
Highly selective, double plasma membrane
What are grana?
Stacks of up to 100 disc-like structures called thylakoids, containing chlorophyll
What links grana together?
Some thylakoids have tubular extensions that join thylakoids inn adjacent grana
Where do the first stages of photosynthesis occur?
The grana (light absorption)
What is the stroma?
A fluid-filled matrix, where stage 2 of photosynthesis occurs (synthesis of sugars)
How are chloroplasts adapted to their function?
Granal membranes- large SA- attach chlorophyll, electron carriers and enzymes
Stroma fluid possesses all enzymes needed for stage 2
Contains DNA and ribosomes so they can quickly manufacture proteins for photosynthesis
What is the cisternae?
The membrane of ER enclose a network of tubules and flattened sacs
What are the functions of the RER?
Provide large SA for synthesis of proteins and glycoproteins
Pathway for transport of materials, especially proteins, throughout the cell
What are the functions of the SER?
Synthesise, store and transport lipids and carbohydrates
What are vesicles?
Structures consisting of liquid or cytoplasm enclosed by a lipid bilayer which transport materials in the plasma membrane
How do vesicles form?
Naturally by secretion and uptake (exocytosis and endocytosis)
What do Golgi vesicles do?
Stores lipids and proteins and transports them into and out of the cell
What does the Golgi apparatus consist of?
Stacks of membranes that make up flattened sacs, cisternae with small rounded hollow vesicles
What does the Golgi apparatus do?
Modifies proteins by adding non-protein components such as carbs. ‘Labels’ them, allowing to be accurately sorted and sent to the correct place