2.1.1 Eukaryotic Cells
What is the nucleolus?
A darker, denser region within the nucleus which assembles ribosomes and manufactures mRNA - it has a vital role in protein synthesis.
What is a eukaryote? Give three examples of eukaryotes.
A eukaryote is any organism which contains a large number of eukaryotic cells. Usually multicellular, eukaryotes include animals, plants and protists.
What forms the bulk of the nucleus?
A granular, jelly-like material called nucleoplasm.
What is inside the mitochondria?
A liquid called the matrix which contains the DNA and also other enzymes to aid respiration.
What is the endoplasmic reticulum?
A series of flattened membranes which encloses many tubules and sacs called the cisternae.
Name some processes that lysosomes are involved in within the body?
Any time something needs breaking down (hydrolysing, catabolic reactions) the lysosome can help. For example, in phagocytosis they hydrolyse pathogens. They also break down and digest worn out organelles, old cells etc.
Why are chloroplasts called the plant version of mitochondria?
Because they have a similar structure and they produce the source of energy.
What do plant cells have that animal cells don't have?
Cell walls, chloroplasts, vacuoles.
What are centrioles? What process are they important in?
Centrioles are barrel-like structures made out of microtubules (proteins) which are important in mitosis as they form the spindle apparatus.
Give three things that are made of microtubules.
Centrioles, flagella, cilia
What is the nuclear envelope like?
Double and it has around 3000 pores - small holes out of which substances can diffuse such as mRNA after it's been made by the nucleolus.
Describe the membrane of the mitochondria?
Double membrane. The inner membrane is called the cristae; it is folded into many projections and coated in enzymes which aid respiration.
What is the Golgi apparatus?
Flattened endoplasmic reticulum called cisternae.
((Are all cell walls made of cellulose? Which aren't?))
Fungi cell walls are made of chitin. Bacterial (prokaryotic cell walls) are made of murein.
Describe the structure of a chloroplast?
Has a double membrane. Contains grana which are stacks of thylakoids. Thylakoids contain chlorophyll, the pigment which absorbs light energy. They also contain a liquid called the stroma which has enzymes and DNA in it.
How is DNA contained in the nucleus?
In a liquid called chromatin which contains chromosomes which are super-coils of DNA-histone complexes. The chromatin condenses to be visible as chromosomes during mitosis.
What's the function of rough ER?
It provides a large surface area for the synthesis of proteins by the ribosomes, and a pathway for the transport of proteins through the cell.
What's the function of smooth ER?
It synthesises, stores and transports lipids and carbohydrates.
Why is the Golgi compared to the post office of the cell?
It's main function is to process, label, package and transport substances like proteins, lipids and carbohydrates - like a post office does with letters.
What are plant cell walls made of?
Microfibrils of cellulose - a beta-glucose polysaccharide which is very strong due to it's straight unbranched chains and the hydrogen bonds between them.
What do the mitochondria do?
Mitochondria are the site of respiration which releases energy from ATP by hydrolysing it. The energy is used by the cell for many processes.
Which three organelles contain DNA? What else do they have in common?
Nucleus, mitochondria and chloroplasts. They also all have a double membrane (an envelope)
Where is the ER found in the cell?
Often it is found continuous with the nuclear envelope, especially rough ER.
Where are ribosomes found in the cell?
Often on Rough Er continuous with the nuclear envelope although they may also be found free in the cytoplasm.
How are organelles helped to move around the cell?
They are aided by actin fibres which contract like muscle fibres to brush them along.
Why are plant cell walls so important? What do they do and what does this allow the plant to do?
They are strong enough the resist the outward forces from turgor pressure so they don;t let the plant cell burst. they prevent the plant cell taking in too much water. this allows plants to live in hypotonic solutions with very high water potentials, without dying.
What do chloroplasts do?
They are the site of photosynthesis - the process by which plants absorb light energy from the Sun and sue it to convert water and carbon dioxide into glucose which can then be used in respiration or stored as energy.
Where do vesicles carry substances to and from?
They carry them from the golgi apparatus and they may either go to other organelles or places in the cell, or they may leave the cell (exocytosis) when the vesicle fuses with the cell membrane.
Why are ribosomes different to other eukaryotic organelles?
They do not have a membrane.
Give two examples of lysosomes.
Those within phagocytes. The acrosome in the head of the sperm cell which helps it break into the cell in fertilization.
Give four functions of Golgi apparatus.
To produce lysosomes, to add carb to protein to make glycoproteins, to package and modify lipids, to secrete carbohydrates
Describe the structure and function of a ribosome.
Two sub-units, one larger and one smaller. No membrane. Eukaryotic cells contain 80S ribosomes (large ones)
How are substances transported in the cell?
Vesicles are spherical membrane sacs which pinch off the ends of the Golgi apparatus to transport substances around the cell.
What are vacuoles important for?
When in a hypertonic solution, water enters the vacuole by osmosis. It swells and pushes the protoplast against the cell wall. this maintains turgor pressure, which keeps the cell firm and rigid to maintain its shape.
Describe the structure of the nucleus.
The nucleus has a double membrane called the nuclear envelope with fluid in between the layers. The bulk of the nucleus is nucleoplasm and it also contains one or more nucleoli, as well as a liquid called chromatin.
What two types of ER are there and what's the difference between them?
Rough ER which is studded with ribosomes and smooth ER which isn't.
What are lysosomes?
Spherical membrane sacs filled with powerful digestive enzymes called lysozymes.
What is the defining feature of a eukaryotic cell?
That the DNA is contained in a double membrane bound nucleus.
((How is the DNA that the nucleus contains different to that contained by the mitochondria and chloroplasts?))
The DNA in mitochondria and chloroplasts is similar to that in prokaryotic cells: shorter, circular and loose in the liquid.
What is the function of the cell membrane and what is it made of?
The cell membrane is made of a phospholipid bilayer with the hydrophilic phosphate heads dissolved in the watery intra and extracellular solutions. The cell membrane forms a partially permeable barrier which controls what enters and leaves the cell and also separates the organelles from other environments.
How do plant cells exchange substances despite the wall?
The cell walls have plasmodesmata which are small holes in them. They also have a middle lamella , the boundary between cells.
Give three ways mitochondria are adapted for respiration.
The cristae increases surface area, the enzymes speed up respiration and there is a great number of mitochondria.
What is the cytoplasm made of and what is its function?
The cytoplasm is a jelly-like, granular watery substance made of a liquid called cytosol. It is the medium in which the other organelles are suspended and through which they move around the cytoskeleton.
What structure helps maintain the ultrastructure of the cell?
The cytoskeleton which is a network of proteins around which the organelles move.
((Suggest the suggested reason that mitochondria and chloroplasts contains DNA yet also a double membrane? ))
The endosymbiotic theory suggests that these organelles were prokaryotic cells which were engulfed but not destroyed by other cells. This would explain the presence and nature of DNA and the double membrane.
What does a vacuole contain?
The membrane of the vacuole is called the tonoplast. Inside is a mixture of cell sap - a watery solution containing dissolved pigments, starch grains, amino acids and salts.
Which organisms can have vacuoles?
plants and animals though only plants have permanent vacuoles.
