2.4 Eukaryotic Cell Structure Flashcards
What is the function of the nucleus?
- Contains DNA (coded genetic information)
- DNA directs the synthesis of proteins and the metabolic activities of the cell (since many of the proteins are enzymes)
What is the purpose of the nucleolus and how does it fulfil it?
- Area within the nucleus made from proteins & RNA
- Responsible for producing ribosomes:
- RNA used to produce rRNA (ribosomal RNA)
- rRNA combined with proteins to form ribosomes for protein synthesis
What is the function of mitochondria?
- The site of production of ATP in the final stages of cellular respiration
- More mitochondria are found in more active cells
- The membrane forming the cristae contains the enzymes used in aerobic respiration
- They contain mtDNA (mitochondrial DNA) to produce their own enzymes and reproduce
What are vesicles?
Membranous sacs that are used to transport materials in the cell.
What are lysosomes?
Specialised forms of vesicles with hydrolytic enzymes which:
- Break down waste material in cells, e.g. old organelles.
- Secrete lysosomal proteases into cytosol, contributing to apoptosis
What is the role of the cytoskeleton?
- Controls cell movement.
- Movement of organelles within the cell.
- Provides mechanical strength to the cell.
What is the endoplasmic reticulum (ER)?
A network of membranes enclosing flattened sacs called cisternae.
What are the functions of the 2 types of endoplasmic reticulum (ER)?
- ER is a network of membranes enclosing cisternae (flattened sacs)
- Smooth ER: lipid and carbohydrate synthesis and storage.
- Rough ER: synthesis and transport of proteins (ribosomes bound to surface)
What is the function of the Golgi apparatus?
Plays a part in modifying proteins and packaging them into vesicles.
Vesicles may be secretory (if proteins are leaving the cell) or lysosomes (which stay in the cell)
What is a prokaryote?
- Single celled organism
- Simple structure of an undivided internal area (cytoplasm)
What is a eukaryotic cell?
- Make up multicellular organisms like animals, plants, fungi
- More complicated internal structure: membrane-bound nucleus (nucleoplasm)
- and cytoplasm containing membrane-bound cellular components
What is the ultrastructure of a cell?
The features that can be seen using an electron microscope.
What is the purpose of organelles?
- providing distinct environments
- providing distinct conditions for different cellular reactions
What is the nuclear envelope?
- A double membrane making up the walls of the nucleus
- Protects DNA from damage in the cytoplasm
- Has nuclear pores to enable movement of RNA into/out of the nucleus for transcription/translation
What is chromatin?
A complex of DNA associated with histone proteins. It coils and condenses to form chromosomes after DNA replication.
What are the components of the cytoskeleton and their purposes?
Microfilaments - contractile fibres made from actin protein. Responsible for cell movement, & contraction (during cytokinesis)
Microtubules - Tubes formed by polymerised globular tubulin proteins, determine the shape of a cell & are tracks for movement of organelles. They make up spindle fibres.
Intermediate fibres - provide mechanical strength to cells, maintain integrity.
What is treadmilling?
- Process by which cells such as phagocytes move
- Actin microfilaments are made up of monomer subunits, which are added and removed to the ends
- Subunits must change shape before they are added to one end, but not the other end.
- Thus subunits are added at a faster rate at one end, increasing in length in one direction allowing a cell to move.
- Concentration of free subunits in cytoplasm determines addition/removal of subunits.
What are centrioles?
- Component of the cytoskeleton present in most eukaryotic cells (except flowering plants, most fungi)
- Composed of microtubules
What is the purpose of centrosomes?
- Formed by 2 associated centrioles
- Assembly and organisation of spindle fibres during cell division
- Thought to play a role in the positioning of flagella & cilia
What is the difference between flagella and cilia?
- Flagella are longer than cilia
- Cilia are usually present in much greater numbers
What is the purpose of flagella?
- Enable cells motility
- May be used as a sensory organelle to detect chemical changes in the environment
What are the 2 types of cilia and their purposes?
Stationary - regulating signalling pathways, maintaining cell homeostasis (present in sensory cells)
Mobile - beat in a rhythmic manner creating a current, cause fluids/objects adjacent to the cell to move (e.g. in trachea moving mucus)
What is the structure of a cilium?
9+2 arrangement:
- Double microtubule in the centre
- Surrounded by nine pairs of microtubules like a wheel
- Pairs of parallel microtubules slide over each other (dynein motor proteins) to move cilia.
Describe the structure of a ribosome.
- Constructed of RNA molecules
- A large subunit and a small subunit, with mRNA in between them
- Growing peptide chain from the large subunit
- Not membrane-bound
