1.2 Cell Structure Flashcards
What organelle (main) do prokaryotes lack?
Prokaryotes are organisms whose cells lack a nucleus
What 2 domains are prokaryotes divided into?
- archaebacteria
- eubacteria
Where are archaebacteria found?
found in extreme environments like high temperatures, salt concentrations or pH (i.e. extremophiles)
What are eubacteria?
traditional bacteria including most known pathogenic forms (e.g. E. coli, S. aureus, etc.)
What different organelles do prokaryotes have (from eukaryotes)?
- nucleoid
- plasmids
- slime capsule
- flagella
- pilli
What is a nucleoid?
region of the cytoplasm where the DNA is located (DNA strand is circular and called a genophore)
What are plasmids?
autonomous circular DNA molecules that may be transferred between bacteria (horizontal gene transfer)
What size is a prokaryote ribosome?
70S
How does the cell wall in a prokaryote differ from a eukaryote?
rigid outer covering made of peptidoglycan
What is a slime capsule?
a thick polysaccharide layer
What is the function of a slime capsule?
used for protection against dessication (drying out) and phagocytosis
What is a flagella?
Long, slender projections containing a motor protein that enables movement
What are pili?
Hair-like extensions
What are the function of pili?
enable adherence to surfaces (attachment pili) or mediate bacterial conjugation (sex pili)
How do prokaryotic cells reproduce?
Binary fission is a form of asexual reproduction used by prokaryotic cells
What are the 3 steps of binary fission?
- The circular DNA is copied in response to a replication signal
- The two DNA loops attach to the membrane
- The membrane elongates and pinches off (cytokinesis), forming two cells
What do eukaryote cells have that prokaryotes don’t?
organisms whose cells contain a nucleus
Eukaryotic cells are compartmentalised by membrane-bound structures (organelles) that perform specific roles
What 4 kingdoms can eukaryotes be categorised into?
- protista
- fungi
- plantae
- animalia
What are protista?
unicellular organisms; or multicellular organisms without specialised tissue
What are fungi?
have a cell wall made of chitin and obtain nutrition via heterotrophic absorption
What are plantae?
have a cell wall made of cellulose and obtain nutrition autotrophically (via photosynthesis)
What are animalia?
no cell wall and obtain nutrition via heterotrophic ingestion
What are organelles?
Organelles are specialised sub-structures within a cell that serve a specific function
What are 3 universal organelles (pro and eukaryote)?
- ribosomes
- cytoskeleton
- plasma membrane
What is the structure of a ribosome?
Two subunits made of RNA and protein; larger in eukaryotes (80S) than prokaryotes (70S)
What is the function of a ribosome?
Site of polypeptide synthesis (this process is called translation)
What is the structure of the cytoskeleton?
A filamentous scaffolding within the cytoplasm (fluid portion of the cytoplasm is the cytosol)
What is the function of the cytoskeleton?
Provides internal structure and mediates intracellular transport (less developed in prokaryotes)
What is the structure of the plasma membrane?
Phospholipid bilayer embedded with proteins (not an organelle per se, but a vital structure)
What is the function of the plasma membrane?
Semi-permeable and selective barrier surrounding the cell
What is the structure of the nucleus?
Double membrane structure with pores; contains an inner region called a nucleolus
What is the function of the nucleus?
Stores genetic material (DNA) as chromatin; nucleolus is site of ribosome assembly
What is the structure of the endoplasmic reticulum?
A membrane network that may be bare (smooth ER) or studded with ribosomes (rough ER)
What is the function of the ER?
Transports materials between organelles
smooth ER = lipids ; rough ER = proteins
What is the structure of the golgi apparatus?
An assembly of vesicles and folded membranes located near the cell membrane
What is the function of the golgi apparatus?
Involved in the sorting, storing, modification and export of secretory products
What is the structure of the mitochondrion?
Double membrane structure, inner membrane highly folded into internal cristae
What is the function of the mitochondrion?
Site of aerobic respiration (ATP production)
What is the structure of the peroxisome?
Membranous sac containing a variety of catabolic enzymes
What is the function of the peroxisome?
Catalyses breakdown of toxic substances (e.g. H2O2) and other metabolites
What is the structure of the centrosome?
Microtubule organising centre (contains paired centrioles in animal cells but not plant cells)
What is the function of the centrosome?
Radiating microtubules form spindle fibres and contribute to cell division (mitosis / meiosis)
What are 3 organelles unique to plant cells?
- chloroplast
- vacuole (large, central and permanent)
- cell wall
What is the structure of a chloroplast?
Double membrane structure with internal stacks of membranous discs (thylakoids)
What is the function of the chloroplast?
Site of photosynthesis – manufactured organic molecules are stored in various plastids
What is the structure of a vacuole?
Fluid-filled internal cavity surrounded by a membrane (tonoplast)
What is the function of a vacuole?
Maintains hydrostatic pressure (animal cells may have small, temporary vacuoles)
What is the structure of the cell wall?
External outer covering made of cellulose (not an organelle per se, but a vital structure)
What is the function of the cell wall?
Provides support and mechanical strength; prevents excess water uptake
What is the structure of the lysosome?
Membranous sacs filled with hydrolytic enzymes
What is the function of the lysosome?
Breakdown/hydrolysis of macromolecules (presence in plant cells is subject to debate)
How do electron microscopes work?
Electron microscopes use electron beams focused by electromagnets to magnify and resolve microscopic specimens
What 2 types of electron microscopes are there?
Transmission electron microscopes (TEM)
Scanning electron microscopes (SEM)
What do TEM produce? (image type)
generate high resolution cross-sections of objects
What do SEM produce? (image type)
display enhanced depth to map the surface of objects in 3D
What are 2 key advantages of electron microscopes compared to light microscopes?
They have a much higher range of magnification (can detect smaller structures)
They have a much higher resolution (can provide clearer and more detailed images)
What is a disadvantage of an electron microscope?
Some disadvantage of electron microscopes are that they cannot display living specimens in natural colours
What is a micrograph?
A micrograph is a photo or digital image taken through a microscope to show a magnified image of a specimen
How could we guess cell function from a micrograph?
Attempts can be made to deduce cell function based on the relative abundance of various organelles
What does it suggest about the cell if it has a large number of mitochondria?
Cells with many mitochondria typically undertake energy-consuming processes (e.g. neurons, muscle cells)
What does it suggest about the cell if it has a large ER network?
Cells with extensive ER networks undertake secretory activities (e.g. plasma cells, exocrine gland cells)
What does it suggest about the cell if it has a large number of lysosomes?
Cells rich in lysosomes tend to undertake digestive processes (e.g. phagocytes)
What does it suggest about the cell if it has a large number of chloroplasts?
Cells with chloroplasts undergo photosynthesis (e.g. plant leaf tissue but not root tissue)
What 4 features of a prokaryotic cell are not found in a eukaryote?
- pili
- flagella (except sperm)
- slime capsule
- plasmid
What size are ribosomes in a prokaryote?
labelled as 70S
What is the cell wall in a prokaryote composed of?
peptidoglycan, (thicker than cell membrane)
