Cell Structure & Diversity 3- Cell Walls & Respiration Flashcards
What is a plant cell composed of?
Cell wall and protoplast
What is the protoplast?
Cell membrane and everything found inside it
What structures are unique to plant cells?
Cell wall, plasmodesmata, chloroplasts and central vacuole
What is the main component of the cell wall?
Cellulose
What is the structure of cellulose?
A glucose polymer that is highly ordered and forms long ribbon-like structures
How does the structure of cellulose help the cell wall?
The highly ordered structure of cellulose makes it very strong and when multiple cellulose ribbons cross link to from microfibrils it makes a strong and inert structure.
What is the first phase of the cell wall and what is involved?
Crystalline Microfibullar Phase which involves cellulose
What is the second phase of the cell wall and what is involved?
Noncrystalline Matrix which involves pectin and hemicellulose polysaccharides as well as a network extension protein
What is hemicellulose?
A heterogenous group of polysaccharides. A long chain of one type of sugar and a short side chain forms a rigid structure.
What is pectin?
Branched negatively charged polysaccharides which bind water and have gel-like properties.
What is the function of extensin?
Extension cross linking of pectin and cellulose dehydrates the cell wall, reduces extensibility and increases strength.
What is controlled by extension cross linking?
Expanding of cells
Where is the cell wall made?
Outside of the cell
What organelles are needed to make the cell wall?
Golgi complex and rough ER
What are the organelles needed for in making the cell wall?
Coordinating synthesis and delivery of cellulose microfibrils, polysaccharides (pectin and hemicellulose) and cell wall proteins (extensins)
Where are cellulose microfibrils made and what by?
At the plasma membrane by rosettes
Where are the polysaccharides made?
At the Golgi complex and then transported to the cell wall using vesicles
What makes extensions?
Rough ER
How are materials for the cell wall transported?
In vesicles by constitutive exocytosis and the vesicles then fuse to the plasma membrane and release the contents outside
What are rosettes attached to?
Cortical Microtubules
How do rosettes make microfibrils?
Move along the microtubules and joins glucose molecules together to make the cellulose microfibril
What is affected by the way the microtubules are laid?
Where the cellulose is formed and therefore the cell shape
What is the middle lamella?
The sticky portion between the cells which sticks them together
What are the functions of the cell wall?
Regulating the shape, providing structural support and preventing excessive water uptake
What happens if the cellulose microfibrils are randomly orientated?
The cell will expand equally in all directions
What happens if the cellulose microfibrils are laid at right angles to the ultimate longitudinal axis?
Cell will expand longitudinally along that axis
How does the cell wall provide structural support?
The protoplast pushes against the cell wall making the cell wall become rigid and therefore maintaining the plant structure
How does wilting occur?
When the protoplast ins’t pushing against the cell wall
What causes wilting?
When water is lost from the cells it reduces the protoplast volume causing it to not press on the cell wall
What happens when water enters a plant cell?
The protoplast expands and pushes against the cell walls. Equal and opposite pressure of the cell wall pushing back prevents the cell getting too large
What does pressure from the cell do?
Limit the volume of water that can be taken up
What are vacuoles important for and why?
Preventing excessive water uptake because they contain water and make up such a large portion of the protoplast
What is a vacuole?
An organelle surrounded by a highly selective membrane which is similar to the plasma membrane
How does water enter the vacuole?
Passively by osmosis
What is found in high concentration in the vacuole and what does this result in?
Solutes which causes water uptake into the vacuole by osmosis
What happens when an animal cell is in a hypotonic solution?
It becomes lysed (burst)
What happens when a plant cell is in a hypotonic solution?
It becomes turgid (normal)
What happens to plant and animal cells in isotonic solution?
They remain normal
What happens to animal cells in a hypertonic solution?
It becomes shrivelled
What happens to plant cells in a hypertonic solution?
It becomes plasmolyzed
Do all plants have a secondary cell wall?
No
When is the secondary cell wall produced?
After cell growth has stopped
How does the secondary cell wall compare to the primary cell wall?
It is thicker and stronger so therefore provides more structural support
What is the structure of the secondary cell wall?
It is made up of multiple layers of microfibrils which are each orientated in different directions so it is thick and strong
Where is the secondary cell wall made?
The secondary cell wall is made closer to the cell because the primary cell wall has already been made
What are the chemical characteristics of the secondary cell wall?
It is made of more cellulose and less pectin as well as lignin
What is lignin?
Lignin is a complex polymer which confers strength and rigidity to the cell wall and also acts to exclude water
What does the secondary cell wall provide structure for?
Specific cell types such as water transporting cells and for the whole plane
What are plasmodesmata?
Intercellular connections which enable cell to cell communication
How is the plasmodesmata made?
The plasma membrane from one cell wraps around to the plasma membrane of the other cell so that it is continuous
What is the size of the plasmodesmata?
Small enough to prevent organelle movements although the endoplasmic reticulum is connected through the plasmodesmata
What does the plasmodesmata allow?
The free exchange of small molecules
Why does the cell need energy?
For mechanical work, to make new materials, for transport and to maintain order
What is meant by mechanical work?
Motor proteins moving vesicles around
What is meant by making new materials?
For growth and division as enzymatic reactions such as cell division require ATP
What is meant by transport?
Molecules moving across membranes against the concentration gradients needs energy.
What is the site of cellular respiration?
Mitochondria
What is the formula for respiration?
C6H12O6 + 602»_space;> 6CO2 + 6H2O + ENERGY
What are the two key compartments of the mitochondria?
Matrix and inner membrane
What is the approximate length of mitochondria?
1-10 micrometres long
How many mitochondria are in a cell?
1-1000’s per cell depending on its energy requirements
What does mitochondria contain?
Mitochondrial DNA and ribosomes but it doesn’t produce all mitochondrial proteins
How many membranes does a mitochondrion have?
2
What are the names of the membranes in mitochondria?
Inner and outer mitochondrial membrane
Where is the matrix found?
Inside the inner mitochondrial membrane
What are cristae?
Folds in the inner mitochondrial membrane
Why are cristae important?
Because they provide a large surface ares for reactions to occur
What is the inter membrane space?
The space between the inner and outer mitochondrial membrane
What is respiration?
When chemical energy from glucose is harvested in three stages which each occur in a different location. Therefore the compartments of the mitochondria are essential for respiration.
What are the three stages of respiration?
Glycolysis, Pyrivate Oxidation and Citric acid cycle and Oxidative Phosphorylation
Where does glycolysis occur?
In the cytosol
What happens during glycolysis?
Sugar (glucose) molecules are broken down into two pyruvate molecules which are 3 carbon molecules
What is the products of glycolysis?
2 pyruvate molecules, ATP and high energy electrons which are stores in an electron storing NADH molecule
Where does Pyruvate oxidation and the citric acid cycle occur?
In the matrix
What happens during pyruvate oxidation?
Pyruvate is converted into Acetyl-CoA and carbon dioxide is also released
What happens during the citric acid cycle?
Acetyl CoA enters the citric acid cycle which extracts ATP and high energy electrons in the NADH and FADH2 carriers
What are the two parts of Oxidative Phosphorylation?
Electron Transport chain and chemiosmosis
Where does the electron transport chain occur?
On the cristae
What happens during the electron transport chain?
Electron carriers (NADH and FADH2) shuttle high energy electrons to the inner mitochondrial membrane and the electrons move through protein complexes which are embedded in the membrane. As the electrons move, protons are pumped across the membrane into the intermembrane space using the energy lost from the electrons.
What complex does NADH electrons enter?
Complex 1
What complex do FADH2 electrons enter?
Complex 2 because they have slightly less energy
What happens as a result of the electron transport chain?
Protons accumulate in the inter membrane space making the proton concentration different on either side of the membrane which is crucial for chemiosmosis.
Where does chemiosmosis occur?
In the inner membrane protein complex - ATP Synthase which spans from the intermembrane space to the mitochondrial matrix.
What happens during chemiosmosis?
The proton gradient means that the protons move through ATP synthase and can power ATP synthesis.
What is ATP synthesis?
When a phosphate group is added to and ADP molecule to make ATP
What does ATP enable?
The continual release of energy
What is the cycle of ATP?
It is continually used and regenerated
How is water formed during respiration?
The hydrogen ions which move through ATP synthase combine with oxygen that the cell has consumed
