Eukaryotic Cells and DNA

Eukaryotes

• Eukaryotes possess a true nucleus and cytoplasmic organelles, with each organelle having its membrane
• They contain a membrane-bound nucleus and a cell wall

DNA

• Eukaryotic DNA is enclosed by a nuclear envelope consisting of two lipid bilayer membranes
• Lamins, which are protein filaments, reinforce the nuclear envelope in animal cells
• Proteins line the nuclear envelope
• The envelope contains nuclear pore complexes that are large, octagonal, and symmetrical, formed from nucleoporin proteins
• Nuclear pores are filled with nucleoporins, and small molecules can pass through them
• RNA and proteins require transport proteins to pass through nuclear pores
• Proteins destined for the nucleus have a tag of amino acids for nuclear localization
• Special proteins bind to this tag and facilitate transport into the nucleus, known as the Nuclear Localization Signal/Signature
• The nucleoplasm fills the nucleus, containing chromatin, a complex of DNA and proteins
• A chromosome consists of a complete DNA molecule along with its associated proteins
• Each DNA and protein combination forms a eukaryotic chromosome
• Eukaryotes have much more DNA
• Chromosomes coil around proteins, forming nucleosomes

Ribosomes

• The nucleus contains nucleoli, which are masses of fibers and granules formed around rRNA coding genes
• rRNA forms in the nucleus and combines with proteins to form ribosomal subunits
• These subunits leave the nucleus through nuclear pore complexes
• They join with mRNA to form a ribosome
• Ribosomes are responsible for protein synthesis and have a large and small subunit
• Eukaryotic ribosomes are larger than prokaryotic ribosomes
• They can be free in the cytosol or attached to membranes (ER)
• Proteins made in the cytosol either remain there, pass into the nucleus, or become components of other organelles
• Proteins made on the ER follow a path to other organelles

Endomembrane System

• The endomembrane system is a system of internal membranous sacs that divides the cell
• This system is connected via vesicles
• The functions of the endomembrane system include: protein synthesis and modification, protein transport, lipid synthesis, and detoxification
• The endoplasmic reticulum (ER) is folded into sheets and tubes to maximize surface area, forming a network of cisternae and compartments
• Folded membranes surround the ER lumen and are surrounded by an aqueous compartment

Rough ER

• Ribosomes stud the outer surface of the rough ER
• It manages proteins by synthesizing, processing, and transporting them
• Proteins enter the ER lumen, fold into their final shape, and are delivered to other regions in small vesicles that pinch off

Smooth ER

• Smooth ER lacks ribosomes and is involved in the production of lipids
• In the liver, it contains enzymes for detoxification
• The ER synthesizes phospholipid bilayer membranes, which are added to the ER or transported
• The amount of smooth and rough ER depends on the cell's needs

Golgi Complex

• The Golgi Complex is a stack of flattened, membranous sacs called cisternae, which are not connected, with 3-8 per cell
• It receives proteins from the ER via vesicles, forming the cis-Golgi network
• Enzymes modify proteins within the cisternae, adding or removing carbohydrates and polypeptides
• Proteins travel to the trans-side once modified and has a mechanism for regulating movement
• Proteins have "zip codes" that determine their destination

Lysosomes

• These are vesicles that contain enzymes to break down complex molecules into monomer subunits (proteins, lipids, nucleic acids) that are then transported across the membrane
• Synthesizes new molecules that are formed from budding off the Golgi complex
• Enzymes are formed in the rough ER, function at pH 5
• They digest dysfunctional organelles through autophagy
• Help with phagocytosis, and fuses with phagocytotic vesicles
• Enzymes then degrade the contents

Mitochondrion

• Performs cellular respiration, and energy rich molecules are broken down into CO2 and H2O
• Sugar + Fats and requires oxygen to create: CO2 + H20 + ATP
• The structure is of 2 lipid bilayer membranes which are a smooth outer membrane and a folded inner membrane (cristae)
• Encloses mitochondrial matrix
• Contains DNA and ribosomes.
• ATP is produced in cristae.

Cytoskeleton

• Consists of all eukaryotes containing microtubules and microfilaments
• Animals have intermediate filaments

Microtubules

• They function like scaffolding made from 13 tubulin filaments side-by-side
• Consists of a linear polymer of globular tubulin dimers which has an alpha and beta tubulin
• Length can change by adding or removing dimers

Microfilaments

• Consist of two polymers of wound actin molecules, which has a positive and negative end

Intermediate Filaments

• They are found in anchoring junctions between cells that keep cells together with intermediate filaments, which resemble button like spots or belts
• These are are the strongest and most durable

Functions of Microtubules

• Maintain cell shape
• Anchor cell organelles
• Provide tracks for vesicles and vesicles use dyneins and kinesins to transport, and use energy from microfilaments
• Transport ER
• Enable movement in animal cells and sperm tail movements
• Separate and move chromosomes

Microfilaments

• Transport nutrients, proteins, and organelles
• Responsible for amoeboid movement
• Myosin walks across

Flagella and Cilia

• Elongated, slender, motile structures that extend from the cell surface
• They are identical and cilia are often shorter, but more numerous
• Flagella provide an oar-like movement to propel through the water
• Cilia moves fluids over cell surface
• Consist of a bundle of microtubules arranged in a circle of nine double microtubules around a single pair (9+2 complex)

Specialized Plant Cell Structure

Chloroplasts

• The site of photosynthesis, and is disc-shaped
• Composed of a double membrane and the inter fluid is referred to as stroma
• Contains thylakoids which are grana when stacked

Amyloplasts

• Colourless, and store starch

Chromoplasts

• Are red and yellow

Plastids

• Have their own DNA genomes and machinery for protein synthesis
• Originated from photosynthetic bacteria
• Are similar in size and both divide through binary fission
• Both have circular DNA molecules
• Both code for ribosomes
• Has a similar bacterial membrane and DNA to bacteria

Central Vacuole

• Large vessicles that make up 90% of plant cell volume
• The turgor pressure supports the cell
• Has a membrane called tonoplast which contains transporter proteins
• Stores salt, organic acids, proteins, and pigments, and waste
• Enzymes break down molecules and has chemical defenses

Cell Wall

• Provides support and contains pressure to protect against pathogens
• Made up of cellulose fibres in a carb network

Initial Cell Wall (PCW)

• Soft and Flexible primary structure
• As cell grows, the PCWlays down in cellulose fibres and branched cabs between PCW and plasmamembrane

Secondary CW

• Is a more rigid and thicker layer that reinforces lignin in wood
• Cell walls are held together by the middle lamella made gel-like polysacharides, also known as pectin

Plasmodesmata

• Both the PCW and SCWare perforated by plasmodesmata, which is a tiny channel
• It is filled with cytosol and creates a continuous surface between cells, while also allowing ions and small molecules to pass

Plasmolysis

• Where the protoplast shrinks and pulls away from the cell wall; occurs when the cell loses water to a hypertonic environment

Animal Cell Surface

Cell Adhesion Molecules

• Animal cells organize into tissues and organs and they create body form and structure
• Glycoproteins embedded in the cell membrane bind to specific molecules for each end
• Bind to specific molecules
• They are partially responsible for cells recognition and play a role in tissue transplant rejection

Cell Junctions

• The tight junctions are tight connect that prevent ions from moving out and seal the spaces between cells
• Anchoring junctions weld cells together, and are more commonly found in tissues that stretch
• Gap junctions open direct channels between cells that allow ions and small molecules to pass

Extracellular Matrix

• Provides protection and support for the body.
• Creates mass of skin that has highly specialized structures
• Proteoglycan which determine consistency and matrix
• Fibronectins organized ECMand bind to receptor proteins