Botany LT # 1 Parts of a Plant Cell, Plasma Membrane, Cell Cycle

What are phospholipids able to do in order to maximize their interaction with water molecules?

Spontaneous self-assemble of phospholipid molecules to maximize their interaction with water molecules.

What does amphipathic mean?

Amphipathic means the molecule has both hydrophilic and hydrophobic domains.

Can the molecules move in the Fluid Mosaic Model, if so how can they move?

there is movement due to them not being covalently bonded together (i.e. rotational / laterally / transverse)

What are the types of membrane proteins?

1. Integral (Surface)

   • anchors & transporters

     & enzymes

2. Peripheral

What are the types of peripheral membrane proteins?

• α-helix : recognition & receptors

• β barrel : transporter channel proteins

• helical bundle : enzymes, transporters & receptors

generally : a helical bundle can be any between α-helix and β barrel

What is H+ -ATPase aka Hydrogen ATPase and what does it do?

• enzyme which pumps protons across cell membrane

• Conversion of ATP to ADP is done by this enzyme

What are Aquaporins?

specialized waterconducting channel protein

( β - barrel)

What is Plastocyanin?

small protein transporting electrons in photosynthesis

What does Cellulose Synthase do?

It synthesizes cellulose in plant cell walls

What are the functions of the Plasma membrane

• Controls the transport of molecules in and out of the cells

• Transmits signals from the environment

• Participates in synthesis and assembly of cell wall

• plant cells are interconnected by fine holes (plasmodesmata; sing.: plasmodesma) in the cell walls

What is the Plasmodesmata and what are its functions?

• membrane tubes crossing the cell walls which allows for the communication & transport between two adjacent cells

• It is contrast to an animal cell where there is intracellular communication through protein channels

What is the protoplast?

Living component of cell connected to neighboring cells via plasmodesmata which may serve for cell to cell communication.

What are the 4 components of the plasmodesmata?

1. Nuclear Envelope

2. Chromatin

3. Nucleolus

4. Nuclear Pores

What is the Cytoplasm responsible for?

It is responsible for holding the components of the cell and protects them from damage

What is the function of the Nucleus

• DNA Storage

• Coordinate cellular activities

• Inner & Outer Membrane

• Perinuclear space : each are made with a phospholipid bilayer for protection

the nucleus is also the control center of the cell

What is the function of the nuclear envelope? Additionally, what are nuclear pores and what are they made up of?

• separates genetic material from enzymes

  • nuclear pores (which are found in the nuclear envelope) are made up of 30 diff nucleoporins, and are used for molecule transport in the nucleus

What is the function of the Nucleoplasm and what is it made of?

• akin to the cytoplasm of the nucleus where everything is suspended

• Complex association of DNA & histone proteins (where chromatin is wrapped around)

What is the function of the nucleolus?

Ribosome factory through transcription of ribosomal DNA

What are Protoplasmic Organelles and where may they be found

Internal membrane bound sacs or compartments

found in the cytoplasm

What are the functions of Ribosomes

Sites of protein synthesis

What is the endoplasmic reticulum and where does its synthesized results get packaged to?

• 3D network of tubules and flatenned system

• The MOST EXTENSIVE, reaching through the cytoplasm

• It synthesizes, processes and packages to:

  • membranes

  • vacuoles

  • secretory pathways

What are the 3 types of cellular membranes?

1. Smooth ER

2. Rough ER

3. Plasma Membrane

What does Post-Translational Modification in the Rough ER modify?

modifies polypeptide chains afer being translated in the cell cytoplasm.

What hormones do the Smooth ER produce, and what shape is the smooth ER? Additionally, why is this the shape of the smooth ER?

Steroidal hormones | It is tubular to increase surface area & efficiency in storage of calcium, detoxification & synthesis

What does the endoplasmic reticulum give rise to, and what are the organelles in this system?

• Endomembrane System

  • Plasma Membrane

  • Golgi Apparatus

  • Nucleus

What is a Peroxisome, what are its functions and where may you find them?

• near the Rough ER

• degradative organelle with a single membrane that neutralizes toxins and free radicals

• Free radical scavengers wherein they actively seek out atoms w/ unpaired electrons by means of a catalase

• plays a role particularly in lipid synthesis [ from Smooth ER —> peroxisomes —> Rough ER ]

What is the Golgi apparatus and what is its function?

• occupies the central position in the secretory pathway

• Receives newly synthesized proteins & lipids from the cis face, then sorts it and sitributes it either to the cellular surface or the vacuoles via the trans face. The in-between pathway is called the medial.

What polysaccharides are assembled in the Golgi Apparatus?

1. Pectin

2. Hemicellulose

Where is cellulose processed?

Cellulose is processed in the Cellulose synthase: a large protein complex

What is a vacuole?

fluid filled compartment enclosed by a tonoplast membrane

(30-90% in volume and 90-98% full of H20 : VACUOLAR SAP )

What do pressure are vacuoles able to control?

Controls turgor pressure due to solutions either being

• Isotonic (=)

• Hypotonic (<solute | cell size expands)

• Hypertonic (<solvent | cell size shrinks)

Note : [ Reservoirs of protons & regulate cystolic pH ]

What are other functions of the Golgi Apparatus in relation to H20 and fruits? Also what enzyme does the GA contain?

• it is a vesicle for storage of H20 and proteins, and to why fruits / vegetables have a flavor profile to them

• It cuts bonds to allow for breakdown and recycling of cell.

  • done by acid hydrolases (in the GA)

What are the enzymes which vacuoles use to break down Carbohydrates, Proteins, Nucleic Acids and Lipids

1. Carbohydrate : Glycosidases

2. Proteins : Protease

3. Nucleic Acid : Nuclease

4. Lipids : Lipases

How do vacuoles regulate pH and homeostasis?

• reservoirs of protons Ca2+ (more protons = acidic)

• Regulates systolic pH

• defense against microbial pathogens (wherein it accumulates toxins via sequesteration of toxic compounds)

• Contains anthocyanin pigmentation

What is the function of the Mitochondria?

produce ATP by means of citric acid cycle, respiration, & ATP Synthase | Is the powerhouse of the cell

Note : The mitochondria is also known to be semiautonomous because it contains its own DNA

What are the 2 membranes of the Mitochondria and what may be found in them.

1. Inner membrane

   • has cristae for additional surface area

2. Outer

The mitochondria also contains 2 membrane bounded compartments, what are these compartments?

1. Intermembrane Space

2. Matrix

We know that the Mitochondria is semi autonomous, why does it need to have this property?

The mitochondria is semi autonomous because they need to produce specific proteins to meet their own requirements, hence why they also have ribosomes and hence why they are semi autonomous.

What is the cell wall and what are its functions?

• Elaborate Extracellular Matrix that encloses each plant cell

• Functions

  1. Protection

  2. Shaping

  3. Structural Support

What are the building blocks of cell walls?

• Sugars

  • More specifically

    • Cellulose (c/o cellulose synthase)

    • Hemicellulose (c/o GA)

    • Pectin (c/o GA)

In the cell wall, what is the description and function of the Primary Cell Wall?

These are thin & extensible walls to account for plant growth. (this is also why they are thin bc they need to grow)

In the cell wall, what is the description and function of the Secondary Cell Wall?

rises once plant matures & formed by depositing new layers inside old ones. Hence it is a thick wall | This cell wall allows permeability in the cell wall and have cellulose and lignin which makes the wall stronger for protection (this is why its thicker)

Which part of the plant are cellulose, hemicellulose, pectin and lignin formed?

The meristem of the plant.

In a plant cell wall, what is the description and function of Cellulose

• most abundant : 15 - 30% of the primary cell walls

• exists in the form of microfibrils in a network of cross-linked glycans

• provides strength to the cell wall

What does hemicellulose do in plant walls?

They help link cellulose fibers together

What is the role of lignin in a cell wall?

They are a complex polymer binding cellulose & hemicellulose in secondary walls

What is the description and function of Pectin in the cell wall?

• Gel-like matrix around the cellulose & hemicellulose network

• Glues the plant cells to each other

• Major component of the middle lamella

What are the function of plastids in plants?

• only found in plants

• Semiautonomous | contain their own DNA (but still relies on nucleus to replicate)

• able to differentiate, didifferentiate & redifferentiate

• storage of metabolites

  • (end product of metabolism)

Why are plastids semiautonomous?

They need to produce some of their own proteins hence they have their own DNA and ribosomes.

What are proplastids and where may they be found?

• These are the precursors to every plastid

• Totipotent (have the total potential to turn into any cell)

• Found in plant stem cells located in the meristem and reproductive tissues

Where may u find the lateral meristem, and what is it for in plants?

• Found at the vascular cambium of the plant

• Responsible for the widening and secondary growth of the plant!

What is the Apical Meristem, specifically where may u find it and what does it do for the plant?

• located at the root / shoot which divide to become the leaves, buds and shoots

• Responsible for the vertical primary growth of said plant

The meristem is a group of ? which are specialized for what

Group of Cells, which are specialized for the production of new cells.

What are Pregranal plastids and in what conditions may they develop?

These are plastids which only develop with the exposure of light, then will they mature into chloroplasts

What are Etioplasts and in what conditions may you find them?

• Transitionary state for plastids

• These develop in the absence of light, lacks chlorophyll & instead has protochlorophyllide

What are chloroplasts responsible for in plants?

responsible for containing chlorophyll which red & blue absorbs light for photosynthesis

When a proplastid becomes illuminated, they develop into chloroplasts. What system develops specifically in the stroma of the plant in this process?

A highly complex thylakoid membrane system develops in the stroma

What is endosymbiosis

Two organisms living together with one inside the other

What may have contributed to the double membrane of chloroplasts?

The Phagocytosis (engulfing of a smaller organelle) of cyanobacteria | Which is evidence of endosymbiosis

What is the thylakoid system a collection of ?

is a collection of membranous stacks

What are photosystems

They are chlorophyllprotein complexes.

What does chlorophyll do and what are they bound to?

They absorb red & blue light. They are protein-bound to photosystems

What do Chromoplasts contain and synthesize?

They contain and synthesize carotene & xanthophyll pigments

What is carotene and where may it be found?

A pigment which displays orange to red | Found in the chromoplast

What is xanthophyll, and where is it found?

A pigment which displays yellow to brown | Found in the chromoplast

During Autumn, we may notice that tree leaves which were once green become brown, why does this happen?

During autumn there is less sunlight, meaning there is less Chlorophyll production which means that the pigmentation of the plants are able to shine through, reflecting the brown color of autumn leaves.

What are Amyloplasts and why are they important?

• unpigmented plastids containing starch granules

• Essential during the night as there is no light to photosynthesize so plants must rely on starch

What is Gravitropism?

Wherein amyloplasts helps the plants which are growing irregularly, grow in the right direction

What are Elaioplasts responsible for storing what macromolecule, and additionally how is this macromolecule stored?

These are involved in storing lipids inside fat droplets called Plastoglobuli

What do Proteinplasts do?

Helps in storage & synthesis of proteins → note these are not the primary site of protein synthesis as that would be the Ribosomes

What are the 3 leukoplasts?

1. Amyloplast

2. Elaioplast

3. Proteinplast

When do Cells divide, and what happens to the cellular components of dividing cells?

• Cells divide only at appropriate times

• They are able to replicate critical cellular components w/ high fidelity (exactly the same)

Why are there Gap Phases in the cell growth process?

Time allotment for the monitoring of the internal & external environments for suitable conditions.

What is the importance of checkpoints in the cell cycle?

This is where the cell cycle performs quality control.

What occurs in the Gap 1 phase of cellular division?

• cells recover from cellular division

• Mostly organelles are replicated

if there is an issue Gap 1S inhibits cells to proceed to the synthesis phase.

What occurs in the S phase?

Checks if the cell is large enough w/ double the chromosomal DNA

What is chromosomal DNA?

It is the Nuclear DNA, different from mitochondrial and cytoplasmic DNA

DNA in the nucleus is what in terms of conservation, and why would this be the case?

DNA in the Nucleus is highly conserved as they are useful in the preservation of the genome of certain plants.

What do cyclic dependent kinases do?

1. these regulates gap phases by binding to cyclins

2. activate protein substrates by transferring a phosphate group from ATP to a molecule via Phosphorylisation

In case of DNA damage, what may Cyclic dependent kinases do?

CDK Inhibitors block the active site of the enzymes in case of DNA damage.

On the cell cycle, where may Cyclic dependent kinases be found the most and why would this be the case?

They would be found before the Mitosis phase, this is because this is the last checkpoint before a cell divides and each CDK is used to check if different parts of a cell are made correctly in order to avoid bad cell division.

What are Kinases

They are enzymes which catalyze the transfer of a phosphate group from ATP to a Molecule

What are the 3 steps of DNA Replication?

1. Initiation

2. Synthesis

3. Termination

What is Initiation in DNA Replication?

• Origin of replication is where DNA synthesis starts.

  • eukaryotes have multiple points of origin as they are more complex & are bigger

  • prokaryotes & simpler bacteria only have one and is generated randomly

What occurs in Synthesis in DNA Replication?

• Disassociation from histone proteins & unwind. Protein binding then takes place.

• DNA polymerase adds nucleotides to the 3’ end of the strand. Then base pairing rules.

What is the direction of DNA synthesis?

• Direction of synthesis would be from 5’ → 3’ !

What occurs during Termination in DNA replication?

• where replication forks meet.

• DNA Polymerase falls.

• The end result is a semi-consecutively replicated DNA strand.

• This means one is newly synthesized and the other is the template to preserve the identity of the parent strand

When DNA terminates, we know that the original strand and the daughter strand now coil together, why is this the case and why must it be done this way?

If there is an error in the daughter strand, the original strand serves as a basis for DNA to know the correct pattern so DNA does not mess up, same goes vise versa.

What is Endoreduplication

This is when a cell undergo extra rounds of DNA synthesis without a necessary cell division, thus producing various copies of DNA

Why do plants need to endoreduplicate?

happens to cells that NEED to be dividing fast or those that have rapid metabolism as a way to conserve resources & energy.

How common is endoreduplication in plants, and in which part of the plant may it occur in?

estimated to occur in 80% of all maturing plants, and it occurs in meristematic tissues

What happens during prophase?

• chromosomes condensation + spindle formation

• nucleolus disintegrates

What happens during metaphase?

• spindle fibers atach to centromeres

• Alignment in the equatorial plate

What happens during anaphase?

• chromosomes pull away to the ends of the cell

• Spindle fibers shorten

What happens during telophase?

• cytoplasm is fully divided

• reformation of nucleolus + organelles

• Disintegration of spindles

• Formation of cell plate guided by the Golgi apparatus

What happens in Cytokenisis?

Involves the phragmoplast ergo the scaffolding from the remnants of spindle fibers which guides the formation of a primary cell wall.

What is DNA stored as before cell division and after cell division

Before : Chromatin

After : Chromosome

During metaphase, it is observed that chromosomes align at the middle, why is this?

1. Central alignment ensures daughter cells to be able to receive the same amount of chromosomes.

2. also allows for spindle checkpoint ensures the proper segregation of chromosomes.