3.4- EUKARYOTIC CELL STRUCTURE Flashcards
What is the name for when each cell type has an internal structure that suits it for its job?
ultrastructure
What do eukaryotic cells have that prokaryotic cells do not?
(2)
distinct nucleus
possess membrane-bound organelles
What can be used to see the structure of organelles within a cell?
electron microscope
What is the most prominent feature of a eukaryotic cell?
nucleus
What does the nucleus contain?
organism’s hereditary material
What does the nucleus do?
controls the cell’s activities
What shape is the nucleus usually?
spherical
Usually what is the diameter of the nucleus?
between 10 and 20μm in diameter
What is the nuclear envelope?
double membrane that surrounds the nucleus
What does the outer membrane of the nuclear envelope continuous with?
endoplasmic reticulum of cell and often has ribosomes on its surface
What does the nuclear envelope do? (2)
controls entry and exit of materials in and out of nucleus
contains reactions taking within in
What do the nuclear pores do?
allow passage of large molecules
Example of large molecules nuclear pores allow the passage of?
messenger RNA out of nucleus
Typically how many nuclear pores are in each nucleus?
3000 pores
What is the diameter of the nuclear pores like?
40-100 nm in diameter
What is the nucleoplasm?
granular, jelly-like material that makes up bulk of nucleus
What do chromosomes consist of?
protein-bound, linear DNA
What is the nucleolus?
small spherical region within the nucleoplasm
What does the nucleolus do? (2)
manufactures ribosomal RNA
assembles ribosomes
Can there be more than one nucleolus in the nucleus?
yes
Functions of the nucleus? (3)
act as control centre of cell through production of mRNA and tRNA and hence protein synthesis
retain genetic material of cell in form of DNA + chromosomes
manufacture ribosomal RNA and ribosomes
What shape is the mitochondria usually?
rod-shaped
What is usually the length of mitochondria?
1-10μm in length
Is there a double membrane around mitochondria?
yes
What does the double membrane around mitochondria do?
controls entry + exit of material
What is done to the inner membrane of the double membrane of the mitochondria?
folded to from extensions known as cristae
What are cristae? (mitochondria)
extensions of the inner membrane
What does the cristae do in some species? (mitochondria)
extend across the whole width of the mitochondria
What do the cristae do?
mitochondria
provide large SA for attachment of enzymes and other proteins involved in respiration
What does the matrix make up? (mitochondria)
makes up the remainder of the mitochondrion
What does the matrix contain? (mitochondria)
protein, lipids, ribosomes, and DNA
What does the substances the matrix contains allow the mitochondria to do?
allows mitochondria to control the production of some of their own proteins
What is also found in the matrix? (mitochondria)
enzymes involved in respiration
What is mitochondria the site of?
aerobic stages of respiration
As mitochondria is the site of the aerobic stages of respiration, what is it responsible for?
production of energy-carrier molecule, ATP, from respiratory substances such as glucose
As mitochondria is responsible for production of ATP what may vary about mitochondria in cells that have a high level of metabolic activity? (2)
number and size of mitochondria
number of their cristae
Examples of metabolically active cells? (2)
muscle cells
epithelial cells
Why do epithelial cells in the intestines require a lot of ATP?
in process of absorption of substances from intestines by active transport
What do chloroplasts carry out?
photosynthesis
What do chloroplasts vary in?
shape and size
Typically what shape are chloroplasts?
disc-shaped
Typically how long is a chloroplast?
2-10μm long
Typically what is the diameter of a chloroplast?
1μm in diameter
What is the chloroplast envelope?
double plasma membrane that surrounds the organelle
How selective is the chloroplast envelope?
highly selective
What is the chloroplast envelope highly selective in?
in what is allows to enter and leave the chloroplast
What is the grana? (chloroplast)
stacks of up to 100 disc-like structures called thylakoids
What is within the thylakoid? (chloroplast)
photosynthetic pigment called chlorophyll
What do some thylakoids have? (chloroplast)
tubular extensions that join up with thylakoids In adjacent grana
What happens at the grana? (chloroplast)
where the first stages of photosynthesis takes place
What is the first stage of photosynthesis? (chloroplast)
light absorption
What is the stroma? (chloroplast)
fluid-filled matrix
What happens at the stroma? (chloroplast)
where second stage of photosynthesis takes place
What is the second stage of photosynthesis?
synthesis of sugars
What is within the stroma? (chloroplast)
number of other structures, i.e. starch grains
How is chloroplast adapted to its function of harvesting sunlight and carrying out photosynthesis? (3)
granal membranes provide large SA for attachment of chlorophyll, electron carriers and enzymes that carry out first stages of photosynthesis. these chemicals attached to membrane in highly ordered fashion
fluid of stroma possesses all the enzymes needed to make sugars in second stage of photosynthesis
chloroplast contain both DNA and ribosomes so they can quickly + easily manufacture some of the proteins needed for photosynthesis
What is the endoplasmic reticulum?
elaborate, three-dimensional system of sheet-like membranes,, spreading the cytoplasm of the cells
What is the ER continuous with?
outer nuclear membrane
What do the membranes enclose? (ER)
network of tubules and flattened sacs called cisternae
What are the two types of ER?
rough endoplasmic reticulum (RER) and smooth endoplasmic reticulum (SER)
What does the RER have?
ribosomes present on the outer surfaces of the membranes
What are the functions of RER? (2)
provide large SA for synthesis of proteins and glycoproteins
provide pathway for transport of materials, especially proteins, throughout cell
What does the SER lack?
ribosomes on its surface
How does the appearance of the SER differ from the RER?
often more tubular in appearance
What are the functions of SER? (2)
synthesise, store and transport lipids
synthesise, store and transport carbohydrates
What cells have a very extensive ER?
cells that manufacture and store large quantities of carbohydrates, proteins and lipids
Examples of cells that have very extensive ER? (2)
liver cells
secretory cells- e.g. epithelial cells that line the intestines
What is the structure of the Golgi apparatus similar to?
SER
How is the structure of the Golgi apparatus different to the SER?
Golgi is more compact
What does the Golgi apparatus consist of?
stack of membranes that make up flattened sacs, or cisternae, with small rounded hollow structures called vesicles
What are the proteins and lipids produced by the ER passed through?
passed through the Golgi apparatus
What does the Golgi do to the proteins made by the ER?
modifies proteins often adding non-protein components i.e. carbohydrates to them
‘labels’ them, allowing them to be accurately sorted + sent to correct destinations
What happens once the proteins and lipids are modified by the Golgi apparatus?
modified proteins and lipids transported in Golgi vesicles which are regularly pinched off from ends of Golgi cisternae
Where may the Golgi vesicles move to and what do they do?
move to the cell surface, where they fuse with the membrane + release contents to outside
Functions of Golgi apparatus (5)
add carbohydrates to proteins to form glycoproteins
produce secretory enzymes, i.e. those secreted by pancreas
secrete carbohydrates, i.e. those used in making cells walls in plants
transport, modify + store lipids
form lysosomes
In what cells is the Golgi apparatus well developed in?
secretory cells- e.g. epithelial cells that line intestines
How are lysosomes formed?
when vesicles produced by Golgi apparatus contain enzymes such as proteases and lipases
What else do the lysosomes contain?
contain lysozymes
What do lysozymes do?
hydrolyse cell walls of certain bacteria
Up to how many lysozymes can be in a single lysosome?
50
What is the diameter of lysosomes like?
1.0 μm
What does the lysosome do to the enzymes?
isolate enzymes from rest of the cell before releasing them
Where can the lysosome release the enzymes?
to the outside
OR
into a phagocytic vesicle within the cell
What are the functions of lysosomes? (4)
hydrolyse material ingested by phagocytic cells, i.e. white blood cells + bacteria
release enzymes to outside of cell (exocytosis) to destroy material around cell
digest worn out organelles so useful chemicals they’re made of can be re-used
completely break down cells after they have died (autolysis)
What types of cells are lysosomes especially abundant in? (2)
secretory cells- i.e. epithelial cells
phagocytic cells
What are ribosomes?
small cytoplasmic granules found in all cells
How can ribosomes occur? (2)
in cytoplasm OR associated with RER
What does the types of ribosome depend on?
depends on cells in which they’re found
What are the two types of cells?
80S and 70S
Where are all 80S ribosomes found?
in eukaryotic cells
What is the diameter of 80S ribosomes like?
around 25μm in diameter
Where are all 70S ribosomes found?
in prokaryotic cells, mitochondria and chloroplast
What is the size of 70S ribosomes like in comparison to 80S ribosomes?
70S ribosomes are smaller
How many subunits do ribosomes have?
two
What are the subunits of ribosomes like?
one large and one small
What do each subunit of the ribosome contain?
contains ribosomal RNA and protein
In what numbers do ribosomes occur in?
in vast numbers
As ribosomes occur in vast numbers what percent of dry mass of a cell do they account for?
25%
What is the ribosome the site of?
protein synthesis
What type of cell is cell walls a characteristic of?
plant cells
What do the cell walls of plant cells consist of?
microfibrils of the polysaccharide cellulose, embedded in a matrix
What characteristic do cellulose microfibrils have?
considerable strength
As cellulose microfibrils have considerable strength what do they contribute to?
to overall strength of cell wall
What features do cell walls have? (2)
consist of number of polysaccharides, i.e. cellulose
there’s a thin layer, called middle lamella, which marks boundary between adjacent cell walls + cements adjacent cells together
What are the functions of the cellulose cell wall? (3)
provide mechanical strength to prevent cell bursting under pressure created by osmotic entry of water
give mechanical strength to plant as a whole
allow water to pass along it and so contribute to movement of water through plant
What are the cell walls of algae made up of?
either cellulose or glycoproteins, or a mixture of both
What are the cell walls of fungi made up of?
mixture of nitrogen-containing polysaccharide called chitin, a polysaccharide called glycan and glycoproteins
What may be termed as a vacuole?
fluid-filled sacs bounded by a single membrane
Within a mature plant cell what is the vacuole like?
one large central vacuole
What is the single membrane around a vacuole called?
tonoplast
What does a plant vacuole contain?
solution of mineral salts, sugars, amino acids, wastes and sometimes pigments
Example of pigment that may be in a vacuole?
anthocyanins
What are the functions of vacuoles? (3)
support herbaceous plants, + herbaceous parts of woody plant, by making cells turgid
sugars + amino acids may act as temporary food store
pigments may colour petals to attract pollinating insects
