2. Eukaryotic Cells Flashcards
Define cell ultrastructure
Internal structure of a cell (organelles present AS WELL AS structure of the organelles)
Define eukaryotic cells
A larger cell with a nucleus and membrane-bound organelles in its cytoplasm
Examples of eukaryotic cells
All animal & plant cells
Fungi
Protoctists
Define prokaryotic cells
A smaller cell that doesn’t have a true nucleus or membrane-bound organelles
Examples of prokaryotic cells
All bacteria
Archaea
Examples of membrane-bound organelles
Mitochondria
Chloroplasts
Vacuoles
4 differences between plant and animal cells
- Plant cells have a cell wall made of cellulose
- Plant cells have a large permanent vacuole containing cell sap
- SOME plant cells have chloroplasts containing chlorophyll
- Plant cells store carbohydrates as starch; glycogen for animals
What does a cell surface membrane look like at very high magnification?
Two dark lines separated by a pale area (plasma membrane)
4 functions of cell surface membrane
- Controls what enters & leaves cell
- Cell recognition (e.g. for immune system)
- Adhesion (cells sticking together - important in tissues in multicellular organisms)
- Signalling (e.g. receptors on surface)
What is the cell surface membrane composed of
A phospholipid bilayer
How wide is the cell surface membrane?
Very thin (10 nm)
Cytoplasm function
Contains organelles & enzymes for reactions
Size of nucleus
10-20 micrometres in diameter (largest organelle!)
Structure of nucleus
Double membrane (nuclear envelope) with nuclear pores (100nm diameter) that allows movement of molecules such as mRNA
What is inside the nucleus?
Nucleoplasm - granular, jelly-like material
How do chromosomes behave?
Visible during cell division but at other times are dispersed as chromatin (unravelled chromosome)
The outer membrane of the nucleus is…
Continuous with the rough endoplasmic reticulum
Functions of the nucleus
- Enables protein synthesis through production of mRNA and tRNA
- Retains genetic material as chromosomes
Structure of nucleolus
One or more darkly staining spherical areas within the nucleus
Is the nucleolus membrane bound?
NO
Function of nucleolus
Site of manufacture of ribosomal RNA and assembly of ribosomes
Size of ribosomes
around 20 nm diameter (smallest organelle)
Where are ribosomes
Free in cytoplasm or bough to rough ER (in eukaryotes)
Are ribosomes surrounded by a membrane?
NO
What are ribosomes made of
rRNA and protein
Function of ribosomes
Site of protein synthesis
Size of ribosomes
80S in eukaryotes
70S in prokaryotes (slightly smaller)
Ribosomes have…
a large and small subunit
Structure of rough endoplasmic reticulum
System of membrane bound, flattened sacs (channels) called cisternae
The cisternae are…
interconnected throughout the cell
Why is the rough ER rough
It’s studded with ribosomes
Proteins and the rough ER
Proteins are synthesised on the ribosomes on the rough ER. They are then passed into the cisternae and carried by vesicles to the Golgi
Which cells have the most rough endoplasmic reticulum?
- Pancreatic cell - produces & secretes insulin
- Cells lining stomach - produce & secrete pepsin
- Cells in salivary glands - produce & secrete amylase
- Pituitary glands - hormones (FSH & LH)
Generally cells that produce lots of protein
Singular of cisternae
cisterna
Structure of Golgi apparatus
A stack of flattened membranous sacs called cisternae
What type of structure does a Golgi have
Dynamic structure: vesicles join from the ER and bud off to form secretory vesicles and lysosomes
Function of Golgi
Sorting, modifying and packaging of polymers (e.g. proteins) for secretion
How are proteins secreted in a cell?
- Protein made on ribosomes enter rough ER
- Protein moves through ER assuming three-dimensional shape en route
- Vesicles pinched off rough ER contain the protein
- Vesicles from rough ER fuse to form flattened sacs of Golgi apparatus
- Proteins modified within Golgi
- Vesicles pinched off Golgi contain modified protein
- Vesicle fuses with cell surface membrane releasing protein
What is the Golgi vesicle?
A small, spherical sac of cytoplasm enclosed by single membrane. Part of Golgi apparatus.
What are lysosomes?
- Vesicles containing up to 50 different hydrolytic enzymes (e.g. proteases, lipases & lysozymes)
- They remain inside the cell!
What do lysozymes do?
Break down bacterial cell walls
What do lysosomes do?
- Fuse with phagocytic vesicles to digest contents in a phagocyte
- Digest old dead cells (autolysis) and worn out organelles
Function of smooth endoplasmic reticulum
Synthesis, storage and transport of lipids and carbohydrates
Compare structure of smooth ER to rough ER and Golgi (apart from having no ribosomes)
Less compact
Why is the smooth ER smooth?
No ribosomes at all
What does smooth ER look like under a microscope?
Lots of little “bubbles” - see OneNote
How long are mitochondria?
Around 1-10 micrometres
What shape are mitochondria?
Rod shaped or cylindrical
Describe membrane of mitochondria
- Double membrane
* Inner membrane folded into extensions called cristae (large surface area for enzymes involved in aerobic respiration)
What does interior of mitochondria contain?
Aqueous solution of metabolites and enzymes (e.g. those involved in Krebs cycle), called the matrix
What does the matrix contain?
Its own DNA and ribosomes
What is the chloroplast?
Site of photosynthesis in green plants and photosynthetic protoctists
How long is a chloroplast?
2-10 micrometres (considered large)
What is the chloroplast surrounded by?
An envelope (double membrane - outer and inner)
The chloroplast has a fluid-filled ____ called the ____
matrix; stroma
What does the stroma contain?
Starch grains
What are thylakoids?
Disc-like structures that have chlorophyll within their membrane
A stack of thylakoids is a…
granum
Plural of granum
grana
What do some thylakoids have?
Tubular structures connecting with an adjacent granum
Chloroplasts have their own…
DNA and ribosomes
Chloroplasts adaptations (3)
- Thylakoid membranes of grana create large SA for attachment of chlorophyll & enzymes involved in 1st stage of photosynthesis
- Stroma contains enzymes required for 2nd stage
- Contains DNA & ribosomes: can quickly make proteins (enzymes) required in photosynthesis
What is the vacuole?
A fluid-filled sac surrounded by a single membrane - the tonoplast
What does the vacuole contain?
A solution of mineral salts, sugars, amino acids, wastes and coloured pigments
What does the vacuole do?
Supports plants by making cells turgid
What do sugars and amino acids in the vacuole act as?
A temporary food store
What else does the vacuole contain?
Pigments (e.g. anthocyanins) - used to attract insects
Structure of plant cell walls
Cellulose microfibrils laid down at different angles and embedded in a polysaccharide matrix
Plant cell wall function
Provides mechanical strength and support, and stops cells bursting.
Are plant cell walls freely permeable?
Yes :)
Middle lamella
Marks boundary between adjacent cell walls & cements cells together
Plasmodesmata
Cytoplasmic connections between plant cells through gaps in their cell walls
What are fungi cell walls made of?
Mixture of chitin and glycoproteins
What are algae cell walls made of?
Either cellulose or glycoproteins, or a mix of both
Does the Golgi contain DNA
NO
Does the smooth or rough ER contain DNA
NO
Do the vesicles contain 70S ribosomes
NO
Do the ER contain 70S ribosomes
NO
Do mitochondria contain 70S ribosomes
YES
Do chloroplasts contain 70S ribosomes
YES
