Cell Structure Flashcards
`Mention four features of the cell surface membrane
- 7 nm in diameter (average)
- Partially permeable
- Phospholipid bilayer
- Controls exchange between the cell and its environment
Give four feautures of the cell wall
- Provides structure and support for the cell
- Comprised of cellulose in plant cells and peptidoglycan in bacteria
- Freely permeable
- Narrow threads of cytoplasm i.e plasmodesmata connect neighbouring plant cells
What is cytoplasm?
The aqeuous, fluid/jelly-like substance which provides a constant environment for the processes of organelles within cells.
What is protoplasm?
The term given to all the contents of the cell.
Give five features of the nucleus
- Largest organelle
- Control cell’s activities
- Comprised of two membranes forming the nuclear envelope
- RNA and ribosomes leave through nuclear pores on the nuclear envelope; proteins, ATP and nucleotides enter
- Contains chromsomes, chromatid and the nucleolus
Mention the roles of chromatin and the nucleolus
- Chromatin is the combination of DNA and proteins (histones) to give DNA its compact shape in the nucleus- they make up chromosomes.
- The nucleolus is responsible for producing ribosomes from the information within its DNA
Describe the mitochondria and their functions
- Surrounded by two membranes with the inner membreane membrane folding to form cristae, which project into the interior which is the matrix
- Main function is carrying out aerobic respiration but synthesize lipids as well
- Transfers energy in the form of ATP
Describe the chloroplast and its funtions
- Surrounded by two envelopes
- Comprised of a membrane system of fluid-filled sacs called thylakoids which stack up in regions to form grana- joined together by lamella
- Photosynthesis takes place here- the light-dependent stage is in the thylakoids where chlorophyll is found; light-independent stage is in the stroma
Describe and give the function of the endoplasmic reticulum
- Made up of a network of flattened sacs called cisternae through which proteins (other molecules) can be transported.
- Continuous with the outside membrane of the nuclear envelope
- The rough endoplasmic reticulum contains ribosomes on its surface and vesicles can break off here to attach to the Golgi body
- The smooth endoplasmic reticulum is responsible for the production of steroids and lipids and a major storage site for calcium ions
What are ribosomes and what do they do?
Mention the Svedberg units of ribosomes in eukaryotes and prokaryotes
- Complexes made from ribosonal RNA and proteins
- They allow all the necessary molecules for protein synthesis (tRNA, mRNA, amino acids and regulatory proteins) to gather up in one place.
Eukaryotes- 80S, prokaryotes- 70s
Describe the Golgi apparatus and its role
It is a stack of flattened sacs called cisternae, formed from vesicles which bud off from the endoplasmic reticulum.
It collects, processes and modifies molecules ( like proteins from the RER) and transports them through the Golgi vesicles; and also produces lysosomes.
What do lysosomes do?
The digestive enzymes (hydrolases) they contain break down any unwanted structures.
What is the significance of vacuoles?
- Because of the concentration of the solution within the vacuole, when water enters it by osmosis the hydrostatic pressure created makes plant cells turgid.
- They contain secondary metabolites like pigments and aromatics/astrigents which help plants interact with their environments
- They act as food reserves, storing sucrose or mineral salts
Describe the structure of microtublues and their role
- Alpha and beta tubulin molecules form a dimer; these join end to end to form protofilaments. 13 protofilaments line up to form a hollow cylinder which is what is termed a microtubule
- Makes up the cytoskeleton of the cell
- Makes up intracellular transport as cell components can travel along the surface
- A spindle of microtubules takes part in nuclear division
- Structure is part of the mechanism cilia and flagella use in movement
Discuss the arrangement and role of centrioles and centrosomes
- Centrioles are made up of a ring of 9 triplets of short microtubules and are needed for the production of cilia, and serve as the basal bodies for it and flagella.
- Two of them lie at right angles to one another and form the centrosome.
- The centrosome is the MTOC for the spindle fibres [microtubules] used in nuclear division
