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
What are the functions of the Golgi apparatus?
Form glycoproteins
Produce secretory enzymes
Secrete carbohydrates
Transport, modify and store lipids
Forms lysosomes
When are lysosomes formed?
Golgi vesicles contain digestive enzymes such as proteases and lipases and they also contain lysozymes
What do lysozymes do?
Hydrolyse the cell wall of certain bacteria
How many enzymes may be contained in a lysosome?
Up to 50
Where do lysosomes release enzymes?
Outside the cell or into phagocytic vesicle
What are the functions of lysosomes?
Hydrolyse material ingested by phagocytic cells
Exocytosis of enzymes to destroy material outside the cell
Digest old organelles
Autolysis
What are ribosomes made of?
Protein and RNA
What are the two types of ribosomes and where are they found?
80S- eukaryotic cells (25nm)
70S- prokaryotic cells, mitochondria and chloroplasts
How many ribosomes are there in each cell?
Accounts for up to 25% of the dry mass
What’s the main characteristic of plant cell cell wall?
Microfibrils of the polysaccharide cellulose, embedded in a matrix
What is the middle lamellae and what does it do?
Thin layer, marks the boundary between adjacent cell walls and cements adjacent cells together
What are the functions of the cell wall?
Mechanical strength for support and allows osmosis as water can pass along it
What are the cell walls of algae made up of?
Cellulose and/or glycoproteins
What are fungi cell walls made up of?
Nitrogen containing polysaccharide chitin, the polysaccharide glycan and glycoproteins
What is a vacuole?
Fluid-filled sac bounded by a single membrane
What’s the membrane around the vacuole called?
Tonoplast
What’s in the solution of the vacuole?
Mineral salts, sugars, amino acids, wastes and some pigments
What’s the function of the vacuole?
Support herbaceous plants
Sugar and amino acids may act as a temporary food store
Pigments colour petals to attract pollinating insects
What does the centriole do?
Spacial arrangement: organise microtubules, position of the nucleus and moves chromosomes in cell division
Formation and movement of cilia and flagella
What are peroxisomes?
Membrane-enclosed organelles containing enzymes involved in metabolic reactions (oxidative)
What’s the cell wall of bacteria made of?
Murein
What’s the normal size range of bacteria?
0.1-10micrometers
What is the role of the cell wall in bacteria?
Physical barrier excludes certain substances and protects against mechanical damage and osmotic lysis
What is murein?
Polymer or polysaccharides and peptides
How thick is the cell wall of bacteria?
10-80nm
What is the role of plasmids in bacteria?
Possesses genes that may aid the survival of bacteria in adverse conditions, produces enzymes that break down antibiotics
What is the role of circular DNA in bacteria?
Possesses the genetic information for the replication of bacterial cells
What is the role of the cell surface membrane in bacteria?
Acts as a differentially permeable membrane layer, which controls the entry and exit of chemicals
What is the role of the capsule in bacteria?
Protects bacterium from other cells and helps groups of bacteria stick together for further protection
What are cilia and flagella made of?
Microtubules
What’s the difference between the plant cells and fungal cells?
Can be multicellular (mushrooms) or unicellular (yeast)
Cell wall is made of chitin
No chloroplasts
What’s the difference between cilia and flagella?
Their length
What’s the difference between algae and plants?
Can be unicellular (chlorella) or multicellular (seaweed)
Chloroplasts are different shapes and sizes, some algae have one long chloroplasts
What are some eukaryotic organisms?
Animal, plant, fungal and algal
What are the receptors on plasma membranes?
Glycoproteins and glycolipids
What size are bacteria?
20-300nm
What does the capsid on the viruses do?
Protein coat which contains attachment proteins
When does cell specialisation initially begin?
The first group of cells in an embryo are identical and as it matures, each cells takes on its own individual characteristics
How does a cell become specialised?
Every cell contains the same genes needed for it to develop into any one of the many different cells in an organism, but only some of the genes are expressed at any one time
What is a tissue?
Aggregation of similar cells that perform a specific function
What do epithelial tissues do?
Line the surface of organs and often have protective or secretory function
What are the two types of epithelial cells?
Thin, flat cells that line organs of diffusion such as the alveoli
Ciliated epithelium cells line ducts such as trachea
Whats the function of the cilia in the trachea’s epithelial cells?
Moves mucus over the surface
What are the functions of the xylem?
Transport water and mineral ions throughout the plant and also give mechanical support
What is an organ?
An aggregation of tissues that combine to provide a variety of functions, although they often have one predominant major function
What tissues are in the stomach?
Muscular tissue to churn and mix the contents
Epithelial tissue to protect the stomach wall and produce secretions
Connective tissue holds together other tissues
What tissues make up a leaf?
Palisade mesophyll, spongy mesophyll, epidermis, phloem and xylem
Are blood vessels organs?
Capillaries aren’t as they are only made up of epithelial cells, veins and arteries are as they have many tissues such as muscular and epithelial
What are organ systems?
A group of organs working together in a single unit to perform particular functions efficiently
What protein is DNA associated with in eukaryotic cells?
Histones
What cells have a capsule?
Some prokaryotic cells
