Module 3 Unit 1 Flashcards
What do all cells have in common?
- all bounded by a selective membrane (phospholipid bilayer)
- all have cytosol
- all contain chromosomes
- all have ribosomes
What is the difference between eukaryotic and prokaryotic cells?
- In eukaryotes, most of the DNA is in an organelle called the nucleus
- In a prokaryotic cell, the DNA is concentrated in a region that is not membrane-enclosed, called the nucleoid
- within the cytoplasm of a eukaryotic cell is a variety of organelles that are absent in almost all prokaryotic cells
- Eukaryotic cells are generally much larger and diverse than prokaryotic cells
- prokaryotic cells are almost always single-celled organisms
- -Some prokaryotes may also have a capsule surrounding the cell wall which protects it from phagocytosis, helps to hold water
- prokaryotes have short fimbriae that help attach to other cells or substrates and longer projections called flagella that have a white-like motion to propel it
What type of cell is bacteria and archaea?
– prokaryotic cells
How does cell size affect its function?
- Cells must be large enough to house DNA, proteins, and structures needed to survive and reproduce, but small enough to allow exchange with the environment.
- The logistics of carrying out cellular metabolism sets limits on cell size
- As a cell increases in size, its surface area grows proportionately less than its volume (cell volume increases at a faster rate)
What is the smallest cell?
- the smallest cells known are bacteria called mycoplasmas, which have diameters between 0.1 and 1.0 μm
1) mollicutes
2) genus mycoplasma
3) M pneumoniae
- the smallest cells known are bacteria called mycoplasmas, which have diameters between 0.1 and 1.0 μm
What are mollicutes?
- Absence of cell wall
- Plasma membrane limiting boundary
- Parasitic/Commensal
What is the genus mycoplasma?
- Small size (150-250nm)
- no DNA homology with known bacteria.
- They have low guanine, cytosine content.
- They exhibit no reversion to walled forms
What is M pneumoniae?
– the smallest free-living organism capable of self-replication (smaller than some viruses)
How do scientists differentiate between different types of bacteria?
- Scientists use Gram stain to classify bacteria by cell wall composition
- Differentiates bacteria by detecting peptidoglycan.
- Gram‐positive bacteria have simple walls with a large amount of peptidoglycan that can absorb gram stains
- Gram‐negative bacteria have an outer membrane and less peptidoglycan so it does not hold on to the stain very well
What are the four basic functions of the organelles in eukaryote?
- The nucleus and ribosomes are involved in the genetic control of the cell.
- The endoplasmic reticulum, Golgi apparatus, lysosomes, vacuoles, and peroxisomes are involved in the manufacture, distribution, and breakdown of molecules.
- Mitochondria in all cells and chloroplasts in plant cells are involved in energy processing.
- Structural support, movement, and communication between cells are functions of the cytoskeleton, plasma membrane, and cell wall
What is the function of the nucleus?
- contains most of the cell’s DNA
- controls the cell’s activities by directing protein synthesis (by making messenger RNA (mRNA)).
- It is surrounded by the nuclear envelope; a double membrane (each a lipid bilayer) that is perforated by pores (pores regulate the passage of proteins and RNA into and out of the nucleus)
- lined by the nuclear lamina, a netlike array of protein filaments that maintains the shape of the nucleus by mechanically supporting the nuclear envelope
What are ribosomes?
- Ribosomes are involved in the cell’s protein synthesis (joining amino acids together according to the instructions in the mRNA sequence)
- Ribosomes are made of a mix of proteins and ribosomal RNA (which is produced in the nucleolus)
- These subunits then exit the nucleus through the nuclear pores to the cytoplasm, where a large and a small subunit can assemble into a ribosome
How does the nucleus direct protein synthesis?
- directs protein synthesis by synthesizing messenger RNA (mRNA) according to instructions provided by the DNA
- The mRNA is then transported to the cytoplasm via the nuclear pores
- Once an mRNA molecule reaches the cytoplasm, ribosomes translate the mRNA’s genetic message into the primary structure of a specific polypeptide
What’s the difference between free and bound ribosomes?
- Free ribosomes are suspended in the cytoplasm and typically involved in making proteins that function within the cytoplasm (ex. enzymes that catalyze sugar breakdown)
- Bound ribosomes are attached to the endoplasmic reticulum (ER) associated with the nuclear envelope and generally make proteins that are destined for insertion into membranes, for packaging within certain organelles such as lysosomes, or for export from the cell (secretion) (ex. cells of the pancreas that secrete digestive enzymes frequently have a high proportion of bound ribosomes
What does the endomembrane system include?
- nuclear envelope,
- the endoplasmic reticulum,
- the Golgi apparatus,
- lysosomes,
- various kinds of vesicles and vacuoles
- plasma membrane
What is the endoplasmic reticulum?
- consists of a network of membranous tubules and sacs called cisternae which separates the internal compartment of the ER (lumen or cisternal space) from the cytosol
- Smooth ER: outer surface lacks ribosomes
- Rough ER: studded with ribosomes on the outer surface of the membrane and thus appears rough
What is the function of the smooth ER?
- synthesis of lipids (sex hormones of vertebrates and the various steroid hormones secreted by the adrenal glands)
- metabolism of carbohydrates,
- detoxification of drugs and poisons (by adding a hydroxyl group to make it soluble -alcohol induces the proliferation of the smooth ER which increases rate of detoxification and thus tolerance to these drugs. Also, because detoxification enzymes have a broad action, the proliferation of smooth ER in response to one drug can increase the need for higher dosages of other drugs as well)
- storage of calcium ions (When a muscle cell is stimulated by a nerve impulse, calcium ions rush back across the ER membrane from the lumen into the cytosol and trigger contractions)
What is the function of the rough ER?
- assemble protein which then depart from the ER in membrane bound vesicles
- As a polypeptide chain grows from a bound ribosome, the chain is threaded into the ER lumen through a pore as it folds into its functional shape in the lumen
- Most secretory proteins are glycoproteins, proteins with carbohydrates covalently bonded to them because of the enzymes in the ER membrane which depart from the ER in transport vesicles
- grows in place by adding membrane proteins and phospholipids (made from precursors in cytoplasm) to its own membrane
- The ER membrane expands and portions of it are transferred in the form of transport vesicles to other components of the endomembrane system.
What is the function of the Golgi apparatus?
- Products travel in transport vesicles from the ER to the Golgi apparatus.
- One side of the Golgi apparatus (cis face) functions as a receiving dock for the product (vesicles fuse with the membrane) and the other (trans face) as a shipping dock (gives rise to vesicles that pinch off)
- Products are modified (according to particular tags or sequences of amino acids) as they go from one side of the Golgi apparatus to the other and travel in vesicles to other sites
- also manufactures some macromolecules
What are the functions of lysosomes?
- A lysosome is a membranous sac containing digestive enzymes to hydrolyze macromolecules
- Hydrolytic enzymes and lysosomal membrane are made by rough ER and then transferred to the Golgi apparatus for further processing
- the three-dimensional shapes of these proteins in the lysosomal membrane protect vulnerable bonds from enzymatic attack
- Lysosomes also use their hydrolytic enzymes to recycle the cell’s own organic material, a process called autophagy; a damaged organelle or small amount of cytosol becomes surrounded by a double membrane (of unknown origin), and a lysosome fuses with the outer membrane of this vesicle and the lysosomal enzymes then degrade it (cell can continually renew itself because of this)
- slow rate of lysosomal action is associated with a range of neurological conditions like alzheimers disease
What is the function of vacuoles?
- large vesicles derived from the endoplasmic reticulum and Golgi apparatus
- food vacuoles are formed by phagocytosis of microorganisms or particles to be used as food by the cell
- protists have contractile vacuoles that pump excess water out of the cell, thereby maintaining a suitable concentration of ions and molecules inside the cell
- In plants, vacuoles may have digestive functions, contain pigments, or contain poisons that protect the plant.
- The central vacuole plays a major role in the growth of plant cells, which enlarge as the vacuole absorbs water; the solution inside the central vacuole, called cell sap, is the plant cell’s main repository of inorganic ions
What is the function of mitochondria?
- the sites of cellular respiration, the metabolic process that uses oxygen to drive the generation of ATP
- The inner membrane divides the mitochondrion into two internal compartments
1) The inter-membrane space is the narrow region between the inner and outer membranes.
2) The mitochondrial matrix contains the mitochondrial DNA, ribosomes, and many enzymes that catalyze some of the reactions of cellular respiration.
- The inner membrane divides the mitochondrion into two internal compartments
- the number correlates with the cell’s level of metabolic activity
- The outer membrane is smooth, but the inner membrane is convoluted, with infoldings called cristae (increase SA of the inner membrane)
- Defects in one or more of the proteins that participate in cellular respiration, decrease the amount of ATP the cell cane make (mitochondrial myopathy which causes weakness, fatigue, muscle deterioration)
What is the function of chloroplasts?
- contain the green pigment chlorophyll, along with enzymes and other molecules that function in the photosynthetic production of sugar
- Chloroplasts are partitioned into compartments:
1) Between the outer and inner membrane is a thin inter-membrane space.
2) Inside the inner membrane is stroma (equivalent to mitochondrial matrix); Contains the chloroplast DNA, ribosomes, enzymes; a network of interconnected sacs called thylakoids; Stacks of thylakoids are called a granum.
- Chloroplasts are partitioned into compartments:
- The membranes of the chloroplast divide the chloroplast space into three compartments: the intermembrane space, the stroma, and the thylakoid space
- The chloroplast is a specialized member of a family of closely related plant organelles called plastids (like amyoplast and chloroplast)
What is the endosymbiont theory?
- states that an early ancestor of eukaryotic cells engulfed an oxygen-using nonphotosynthetic prokaryotic cell (mitochondrion)
- Eventually, the engulfed cell formed a relationship with the host cell in which it was enclosed, becoming an endosymbiont and over the course of evolution they merged into a single organism (a eukaryotic cell with a mitochondrion)
- At least one of these cells may have then taken up a photosynthetic prokaryote, becoming the ancestor of eukaryotic cells that contain chloroplasts