cell structure

atypical cell structure in eukaryotes

aseptate fungal hyphae - multinucleate

skeletal muscle - multinucleate

they are quiet big, elongated cytoplasm with more than one nucleus, not strictly seperated

red blood cells - no nucleus

phloem sieve tube elements - no nucleus

no nucleus, organelles, cannot reproduce, cannot make proteins

prokaryote cell structure

cell wall (peptidoglycogen), plasma membrane, cytoplasm, naked DNA loop, 70s ribosomes.

+pili and flagella/flagellum

features common to eukaryotes (functions specified later)

1. plasma membrane

2. compartmentalized cytoplasm

3. 80s ribosome

4. nucleus and chromosomes made of DNA bound to histone contained in a double membrane with pores

5. mitochondria

6. ER

7. golgi apparatus

8. vesicles or vacuoles containing lysosomes

9. cytoskeleton of microtubules and microfilaments

animal cell structures

1. plasma membrane

2. compartmentalized cytoplasm

3. 80s ribosome

4. nucleus and chromosomes made of DNA bound to histone contained in a double membrane with pores

5. mitochondria

6. ER rough

7. ER smooth

8. golgi apparatus

9. secretory vesicles

10. lysosomes

11. cytoskeleton of microtubules and microfilaments

plant cells

1. plasma membrane

2. compartmentalized cytoplasm

3. 80s ribosome

4. nucleus and chromosomes made of DNA bound to histone contained in a double membrane with pores

5. mitochondria

6. ER rough

7. ER smooth

8. golgi apparatus

9. sap vacuole

10. cytoskeleton of microtubules and microfilaments

11. chloroplasts

comparison between animal plant and fungi

cell wall: plant (cellulose) fungi (chitin)

vacuole: animal (small, scattered, stores materials and waste), plant (large central vacuole, maintains turgor pressure), fungi (both small and large)

plastids (two outer memebrane and internal membrane sacs): plants (chloroplasts, chromoplasts,amyloplast)

centrioles (cylindrical organelles that organise the assemply of structures composed of microtubles): animal (in mitosis and meiosis)

cilia/flagella (generate movement of a cell or movement of fluid adjacent to the cell): some animal cells

magnification eqaution

image size = actual * magification

fluorescent staining

Stains bind to some chemicals but not others. Fluorescence is when a substance absrobs light and then re-emits it at a longer wavelength

immunofluorescence

antibodies that bind to particular antigens in the cell are produced, then fluorescent markers of different colours are linked to these antibodies. colors

freeze fracture

produces images of surfaces within cells. A sample is plunged into liquid propane (-190oc) so it rapidly freezes, and a steel blade is then used to fracture the sample. The fracture goes through the weakest point of cells; some ice at the fracture surface is removed by vaporization in a process called etching. A vapor of platinum or carbon is then added to form a coating

Offers cross-section perspectives.

Gives a unique image of parts of cells.

Was used to split membranes and analyse membrane structure.

cyogenic electron microscopy

used for researching the structure of proteins

• Thin layer of pure protein solution is applied to a grid

• Solution is flash frozen to create smooth vitreous ice and to prevent the formation of water crystals

• The gird is then placed in an electron microscope and  detectors record the pattern of electrons transmitted by individual protein molecules

Doe not need crystals

Analyses proteins in the instant in time when the water around them froze.

Give resolutions of 0.12 nm

light microscope ad/disad

ad: Cheaper to run, live or dead specimen, no vacuum required

disad: Lower magnification

light micro using fluorescence

Allows labelling of organelles and other features of interest

Electron microscope

ad: Greater magnification

disad: Dead specimen only, vacuum required, give black white images, expensive

origin of eukaryotic cells by endosymbiosis

Eukaryotes evolved from a common unicellular ancestor that had a nucleus and reproduced sexually. to overcome a small sa:v ratio, ancestral prokaryote cells developed folds in their membrane to form rough ER and nucleus → future eukaryotic cells. Mitochondria/chloroplasts are then evolved by endosymbosis as it gave the cells a competitive advantage

endosymbiosis

one organism lives within another. One organism must have engulfed the other by the process of endocytosis. If the relationship is beneficial to both, the engulfed organism is not digested.

evidence for endosymbiosis

similar size to modern prokaryotes → bacteria can’t have a mitochondria

Both contain singular circular nonmembrane-bound DNA

has 70s ribosomes to synthesis their own proteins

Able to transcribe mRNA from their DNA

Mitochondria + Chloroplasts reproduce through binary fission

chloroplasts + mitochondira have double membranes resulting from the endocytosis of original small prokaryotic cell.

cell differentiation

cause newly formed cells to become more specialised and distinct from one another as they develop. it occurs when common parental cells (stem cells) develop into different cell types.

basis for differentiation: different patterns of gene expression often triggered by changes in the environment

key features of stem cells

1. undifferentiated

2. differentiating into specialized cells

3. endlessly reproducing

stem cells in plants

found in meristemic tissue

internal environment gene control:

1. there are some gene regulatory proteins that attach to specific sections of DNA which can either inhibit or stimulate that gene to be expressed.

2. DNA methylation, which is a chemical process that causes the DNA to be so tightly coiled, making it difficult to be transcribed)

3. DNA has attached proteins called histones. If histones undergo the process of acetylation it ends up causing  DNA to be loosely packed which increases the genes expression in those areas.

4. Hormones like steroids are able to enter the cell and interact with specific steroid receptor proteins that  in turn control gene expression.

multicellular specialized tissue

1. more efficient use of resources

2. longer life spans

3. better protected

4. consuming smaller organisms

5. has evolved repeatedly