Cell Structure

Prokaryotic & Eukaryotic structure and organelles

Plasma Membrane

• controls the exchange of materials between the internal and external cell environment

• semi-permeable ; contains protein channels

• formed from a bilayer of phospholipids

Nucleus

• in all eukaryotic cells(except red blood cells) — surrounded by nuclear envelope

• Nuclear pores are important channels for allowing mthe RNA and ribosomes to travel out of the nucleus

  • allows enzymes(e.g DNA polymerases) and signalling molecules to travel in

• contains chromatin

  • DNA tightly wound around histone proteins

Rough ER

• found in plant and animal cells

• contains ribosomes

• modifies and processes proteins made by the ribosomes

• transports proteins using vesicles

• formed from folds of continuous membrane

Smooth ER

• no ribosomes

• produces lipids, cholesterol, and hormones

• detoxification - breaks down toxins

Ribosomes

• each ribosome is a complex of rRNA and proteins

• constructed in the nucleolus

• attatchd to the rough ER

• site of translation(protein synthesis)

Golgi Apparatus

• flattened sacs of membrane called cisternae

• modifies proteins and lipids before packaging them into Golgi vesicles — vesicles then transport them

• Proteins that pass through

  • exported(e.g. hormones like insulin)

  • put into lysosomes(e.g. hydrolytic enzymes)

  • delivered to membrane-bound organelles

Mitochondria

• site of aerobic respiration

• generates energy(ATP)

• small circular pieces of DNA & ribosomes are found in the matrix

Vesicles

• membrane-bound sacs for transport and storage

  • e.g. golgi vesicles transport proteins from the Golgi apparatus around the cell

Lysosomes

• contain digestive enzymes

• breaks down waste materials(worn-out organelles)

• used extensively by cells of the immune system and in apoptosis

• destroys pathogens(white blood cells)

Cytoplasm

• contains dissolved solutes(e.g. carbohydrates, lipids, etc…)

• gelly-like fluid —> cytosol

Microtubules & Microfilaments

Microtubules

• makes up the cytoskeleton

• made up of a & B tubulin proteins —> dimers —> protofilament

• strucutural support & transportation

Microfilaments

• smallest of the 3 network fibers

• made up of actin

• elongation and contraction

Intermediate Filaments

• provide mechanical support

Chloroplasts

• larger than mitochondria and surrounded by a double-membrane

• site of photosynthesis: produces glucose

  • light-dependent stage(thlyakoids)

  • light-independent stage(stroma)

• contains a green pigment - chlorophyll

Cell Wall

• found only in plant cells

• offers structural support & formed outside of cell wall

• structural support is provided by polysaccharide cellulose in plants / peptidoglycan in bacterial cells

• freely permeable

Large Permanent Vacuole

• sac in plant cells with a selectively permeable membrane

• animal cells contain temporary, small vacuoles

• stores water & nutrients

• provides structure support

DNA

• controls the production of enzymes and other vital proteins

• contains all genetic material

Capsule

• some prokaryotes(e.g. bacteria) are surrounded by a final outer layer —> slime capsule

• helps to protect bacteria from drying out and from attack by cells of the immune system of the host organism

Flagellum & Pilli

Flagellum

• long, tail-like structures that rotate

  • enables the prokaryotes to move

Pilli

• shorter and thinner structures than flagella

• assists with movement, avoidance of attack by white blood cells,

  • conjugatation(the sexual mode for bacteria)

  • Help bacteria adhere to cell surfaces

Striated Muscle Fibres

• longer than typical cells

• have multiple nuclei surrounded by a single membrane

• formed from multiple cells fused together that work together as a single unit

Aseptate Fungal Hyphae

• have long, narrow branches —> hyphae

  • hyphae have cell mebranes, cell walls and septa

• aseptate fungal hyphae do mot have septa —> multinucleated with continuous cytoplasm

Red blood cells

• do not contain a nucleus

  • reason: to enable the cell to carry a large golume of the oxygen bidning pigment haemoglobin

• biconcave shape due to lack of nucleus —> have maximum surface area to improve their oxygen carrying capacity

Phloem sieve tubes

• transporting dissolve substances(e.g. sucrose)

• no end cell wall and lack many cell organelles(e.g. nuclei, mitochondria, & ribosomes)

• can only survive due to presence of companion cells

Endosymbiosis

• when on organism lives within another

• relationship is beneficial if the engulfed organism is not digested

• one organisms must have engulfed the other by the process of endocytosis for endosymbiosis to occur

Endosymbiotic Theory

• Explanation for the evolution of eukaryotic cells

• Evidence for the theory comes from structure of mitochondria & chloroplasts

  • possession of DNA

  • cell membrane

  • replication

Heterotrophic Cells

• ancestral prokaryote cells develop folds in their membrane

  • from these infoldings organelles such as the nucleus and rough ER formed

• a larger anaerobically respiring cell engulfed a smaller aerobically respiring prokaryote

• gave the larger cell a competitive advantage with a ready supply of ATP and gradually evolved into the heterotrophic eukaryotes with mitochondria

Autotrophic cells

• Over time, photosynthetic prokaryotes engulfed by heterotrophic eukaryotic cells evolved into chloroplasts, and the heterotrophic cells into autotrophic eukaryotic cells

Cell Differentiation

• the process by which an specialized cell develops into a more specialized cell type with a distinct structure and function

Specialisation

• enables cells in a tissue to function more efficiently as they develop specific adaptations for that role

Gene Expression

• Differentiation occurs through changes in gene expression, where certain genes are turned on or off, leading to the synthesis of specific proteins that dictate the cell's characteristic

Multicellularity

1. in multicellular organisms, specialized cells of the same type group together to form tissues

2. a tissue is a group of cells that work together to perform a particular function

3. different tissues work together to form organs

4. different organs work together to form organ systems

Optical(light) Microscopes

• use light to form an image - limits the resolution of optical microscopes

  • using light, it is impossible to resolve two objects closer than half the wavelength of light

• can be used to observe eukaryotic cells, their nuclei and possibly mitchondria and chloroplasts

• cannot be used to observe smaller organelles(e.g. ribosomes, ER, or lysosomes)

Electron Microscopes

• use electrons to form an image

• greatly increases resolution compared to optical microscopes - gives a more detailed image

• can observe small organelles(e.g. ribosomes, ER and lysosomes)

HI MR GREN

1. Homeostasis: Maintenance of a constant internal environment

2. Metabolism: the sum of all the chemical reactions that occur within an organism

3. Response: As the environment changes, the organism adapts

4. Growth: the development of an organism

5. Reproduction: the ability to produce offspring

6. Excretion: the ability to release waste or harmful materials to the surrounding environment

7. Nutrition: the ability to acquire the energy and materials needed to sustain life

Nuclear Envelope

• Nuclear envelope has a double membrane structure

• Nuclear pores control the regulation of substances/materials in and out of the cell; selectively permeable membrane

• Contains nuclear pores throughout the membrane

• Nuclear lamina provides structural support to nuclear envelope

• Nuclear lamina helps regulate DNA replication

• Nuclear lamina is involved in cell division regulation