Topic 5 - Cell Structure and Function Flashcards
Cell theory
- All organisms are made of cells, and the life processes of metabolism and heredity occur in these cells
- Cells are the smallest units of life
- Cell arise from previously existing cells
Cell size
- Cells must be small enough to allow small molecules (such as water, oxygen and carbon dioxide) enough time to quickly diffuse in and out
- As a cell increases in size, its surface area-to-volume ratio decreases
- The higher the surface area-to-volume ratio, the shorter the distance from the outside to the inside of the cell
As a cell increases in size, its surface area-to-volume ratio…
Decreases
What four components do all cells share?
- Plasma membrane
- Cytoplasm (cytosol)
- DNA
- Ribosomes, which synthesize proteins
Prokaryote
A simple, mostly single-celled (unicellular) organism that lacks a nucleus or any other membrane-bound organelle
Where is prokaryotic DNA located?
The nucleoid region, the cell’s central part, as a single circular chromosome
True or false: most prokaryotes have a cell wall
True
True or false: prokaryotes are significantly smaller than eukaryotes
True
How do eukaryotes compensate for a lower surface area-to-volume ratio than prokaryotes?
- Cell division
- Folding of the cell membrane
- Becoming flat/thin/elongated
- Developing organelles for specific tasks
Eukaryotic cells have…
- A membrane-bound nucleus
- Membrane-bound organelles
- Several, rod-shaped chromosomes
Describe the nucleus and its components/functions.
- Organelle that houses the cell’s DNA and directs synthesis of ribosomes and proteins
- Nuclear envelope: outermost boundary; punctuated with pores that control the passage of ions, molecules, and RNA into and out of the nucleus
- Chromatin: unwound protein-chromosome complexes (DNA)
- Nucleolus: body within nucleus that is responsible for assembling ribosome subunits; makes RNA
Describe ribosomes and their functions.
- Cellular structures responsible for protein synthesis
- Ribosomal RNA (rRNA) and protein
- Large and small subunits
Where are ribosomes found?
On the RER or floating freely in the cytoplasm.
Describe the rough endoplasmic reticulum (RER) and its functions.
- Site of protein synthesis (ribosomes)
- Continuous with nuclear envelope
- Proteins made on RER are deposited within a membrane that buds off and transports proteins through the cell
- Glycosylates proteins (modifies them by adding a sugar molecule)
Describe the smooth endoplasmic reticulum (SER) and its functions.
- Continuous with RER but lacks ribosomes (i.e. smooth)
- Synthesis of carbohydrates, lipids, and steroid hormones
- Detoxification of drugs and poisons
- Releases Ca+ for muscle contractions
Describe the Golgi apparatus and its functions.
- Series of stacked membranes that sort, tag, and package lipids, proteins and carbs for distribution
- Modification and transport
- Final folding of protein takes place in Golgi bodies
Describe mitochondria and their functions.
- The “power house of the cell”
- Responsible for making adenosine triphosphate (ATP), the cell’s main energy-carrying molecule
- Oval-shaped with double membranes (inner and outer membrane)
- Inner membrane is highly folded and embedded with enzymes used to convert food energy into ATP
- Cellular respiration
Describe chloroplasts and their functions.
- Carries out photosynthesis
- Three major compartments: intermembrane space, stroma, and granum
Describe lysosomes and their function.
- Membrane-enclosed digestive enzymes
- Present in animal cells
- Breakdown nutrients (phagocytosis), bacteria, damaged organelles (autophagy)
Describe peroxisomes and their function.
- Carry out oxidation reactions that break down fatty acids and amino acids
- Detoxify hydrogen peroxide (H2O2) with catalase
Describe vesicles and vacuoles and their functions.
- Membrane-bound sacs that function in storage and transport
- Contractile vacuoles pump water out of freshwater protists
- Central vacuoles in plants store water and other chemicals
Describe centrosomes and their components/functions.
- Microtubule organizing centers (MTOCs) - all microtubules originate from the centrosome
- Facilitates the organization of the spindle poles during mitosis
- While both animal and plant cells have microtubule organizing centers (MTOCs), animal cells also have centrioles associated with the MTOC
- Centrioles aid in cell division
- Found near nuclei of animal cells
Describe the plasma membrane and its functions.
- Phospholipid bilayer with embedded proteins that separates the internal contents of the cell from its surrounding environment
- Provides protection for the cell
- Controls the passage of organic molecules, ions, water, and oxygen into and out of the cell
Describe the cell wall and its functions.
- Rigid covering that protects the cell, provides structural support, and gives shape to the cell
- Made of cellulose embedded in sugars and proteins
- Present in plant cells
Endosymbiosis
A mutually beneficial relationship in which in which one organism lives inside the other
How did eukaryotes evolve through endosymbiosis?
- Ancestral prokaryote was engulfed by ancestral eukaryote and failed to digest
- Engulfed bacterium provided energy to the host, was protected and provided with nutrients
What is the main evidence that supports the evolutionary origin of mitochondria and chloroplasts through endosymbiosis?
- Bacteria, mitochondria, and chloroplasts are similar in size
- Mitochondria and chloroplasts have circular DNA and ribosomes like modern prokaryotes
- Inner membranes of mitochondria and chloroplasts suggest engulfing process (phagocytosis)
- Mitochondria and chloroplasts reproduce with binary fission just like modern prokaryotes
Describe the cytoskeleton and its functions.
Protein fiber network that collectively maintains the cell’s shape, secures some organelles in specific positions, allows cytoplasm and vesicles to move within the cell, and enables unicellular organisms to move independently
True or false: intermediate filaments are only structural in function and have no role in cell movement.
True
Describe microfilaments/actin filaments and their functions.
- Helical rods made of globular actin (protein)
- Help cells move, change shape (i.e. muscle contraction) and bear tension
Describe intermediate filaments and their functions.
- Fibrous, rope-like
- Purely structural in function
- Bear tension, anchor organelles and give cells shape.
Describe microtubules and their functions.
- Hollow tubes made of globular tubulin (protein)
- Provide rigidity and shape
- Serve as tracks for organelles and chromosomes - pull replicated chromosomes to opposite ends of a dividing cell
- Basis of cilia and flagella
- Assembled in centrosome (microtubule organizing organizing center)
Describe cilia and their functions.
- Hair-like structures that allow movement of the cell (locomotion)
- Short and numerous
Ex. found in paramecia
Describe flagella and their functions.
- Thread-like structures that allow movement of the cell (locomotion)
- Long and less numerous
Ex. found in some prokaryotes and only sperm cells in eukaryotes
List the three types of fibers within the cytoskeleton from smallest to largest diameter.
Microfilaments, intermediate filaments, microtubules
Describe the extracellular matrix (ECM) of animal cells and its functions.
- A large network of proteins and other molecules that surround, support, and give structure to cells and tissues in the body
- Made of collagen and other glycoproteins
- Functions in support, adhesion, movement, and regulation
Cell-to-cell interactions
Multicellularity requires cells to work together through identification, physical connections, and communications
Surface proteins
- Give cell identity (glycoproteins)
- Major Histocompatibility Complex (MHC) - identification of “self” and “non-self”
- Glycolipids (i.e. blood type markers A, B, and O)
List the intercellular junctions in eukaryotes
- Plants: plasmodesmata
- Animals: tight junctions, anchoring junctions (desmosomes), gap junctions
Describe plasmodesmata and their functions.
- Channels that pass between adjacent plant cells’ walls, connect their cytoplasm, and allow transporting of materials from cell to cell.
Describe gap junctions and their functions.
- Channels between adjacent cells that allow for transporting ions, nutrients, and other substances that enable cells to communicate
Describe tight junctions and their functions.
- Watertight seals between two adjacent animal cells
- Proteins tightly hold the cells against each other
- Barrier function - control paracellular permeability
Describe anchoring junctions (desmosomes) and their functions.
- Provide anchorage sites for intermediate filaments important for the maintenance of tissue architecture (e.g. epithelial cells)
- Act like “spot welds” between adjacent cells
