2.4 Eukaryotic cell structure Flashcards
Microscopes not only make cells visible, what also do they do?
they also enable us to look deep inside individual cells
The basic unit of all living things is the cell. What are the two fundamental types of cell?
prokaryotic and eukarytoic
What are prokaryotes?
single-celled organisms with a simple structure of just a single undivided internal area called the cytoplasm
Development of microscopes has allowed biologists to discover increasing amounts of detail of cell ultrastructure.
The increased knowledge of structure has led to a better understanding of cell structure
What is the cytoplasm composed of
cytosol, which is made of water, salts ad organic molecules
What do eukaryotic cells make up?
multicellular organisms like animals, plants and fungi
Eukaryotic cells have a much more complicated internal structure, containing what?
a membrane bound nucleus (nucleoplasm) and cytoplasm, which contains many membrane-bound cellular components
Chemical reactions are the fundamental processes of life, in cells what do they require?
both enzymes and specific reaction conditions
What does metabolism both involve?
1) the synthesis and the breaking down of molecules
What is synthesis?
building up
Different sets of reactions take place in…
different regions of the ultrastructure of the cell
Where do reactions take place?
in the cytplasm
what is the cell cytoplasm separated from?
the external environmnt by a cell-surface membrane
In eukaryotic cells, the cytoplasm is divided into many different what?
membrane-bound compartments, known as organelles
What do organelles provide
distinct environments and therefore conditions for the different cellular reactions
Membranes are _______ ________ and control the ______ of substances into and out of the ____ and ________
i) selectively permeable
ii) movement
iii) cell
iv) organelles
Membranes are effective what?
barriers in controlling which substances enter and exit cells
What is a drawback of membranes?
fragile
The nucleus contains what?
coded genetic information in the form of DNA molecules
What does DNA do?
direct the synthesis of all proteins required by the cell (although this protein synthesis occurs outside of the nucleus at ribosomes)
DNA can direct the synthesis of all proteins required by the cell. What does this mean DNA can do and why?
i) DNA controls the metabolic activities of the cell
ii) as many of these proteins are the enzymes necessary for metabolism to take place
What is often the biggest single organelle in the cell?
nucleus
Where is DNA contained and why?
within a double membrane called a nuclear envelope to protect it from damage in the cytoplasm
What does the nuclear envelope (double membrane) contain?
nuclear pores that allow molecules to move into and out of the nucleus
Why can’t DNA itself leave the nucleus to the site of protein synthesis in the cell cytoplasm?
it is too large
DNA is too large to leave the nucleus to the site of protein synthesis in the cell cytoplasm?
transcribed into smaller RNA molecules, which are exported via the nuclear pores
What do DNA associates with and what does it form?
i) proteins called histones
ii) a complex called chromatin
What does chromatin do?
coils and condenses to form structures known as chromosomes
When do chromosomes only become visible?
when cells are preparing to divide
What is the nucleolus?
an area within the nucleus, responsible for producing RIBOSOMES
What is the nucleolus composed of?
proteins and RNA
What is RNA used for?
to produce ribosomal RNA (rRNA) which is then combined with proteins to form the ribosomes necessary for protein synthesis
What is the singular for mitochondria?
mitochondrion
What are mitochondria?
the site of the final stages of cellular respiration, where the energy stored in the bonds of complex, organic molecules is made available for the cell to use by the production of the molecule ATP
The number of mitochondria in a cell is generally a reflection of what?
the amount of energy it uses, so very active cells usually have a lot of mitochondria
Mitochondria have a _______ ________
double membrane
describe the inner membrane of the mitochondria
highly folded to form structures called cristae and the fluid interior is called the matrix
What does the membrane forming the cristae in mitochondria contain?
the enzymes used in aerobic respiration
Mitochondira also contain a small amount of ___, called _________ __
DNA, mitochondrial (mt) DNA
What can the mitochondria produce and how?
can produce their own enzymes and reproduce themselves
What are vesicles?
membranous sacs that have storage and transport roles
What do vesicles consist of?
simply of a single membrane with fluid inside
What are vesicles used for?
to transport materials inside the cell
What are lysosomes?
specialised forms of vesicles that contain hydrolytic enzymes
What are lysosomes responsible for
breaking down waste material in cells, including old organelles
What system do lysosomes play an important part in and why?
immune system as they are responsible for breaking down pathogens ingested by phagocytic cells
What do lysosomes also play an important role in other than the immune system?
programmed cell death or apoptosis
Where is the cytoskeleton present?
throughout the cytoplasm of all eukaryotic cells
What is the cytoskeleton?
a network of fibres necessary for the shape and stability of the cell
How are organelles held in place?
by the cytoskeleton
What does the cytoskeleton control?
cell movement and the movement of organelles within cells
What three components to the cytoskeleton have?
1) microfilaments
2) microtubules
3) intermediate fibres
What are microfilaments
contractile fibres formed from the protein actin
What are microfilaments responible for?
cel movement and also cell contraction during cytokinesis
what is the process cytokinesis?
the cytoplasm of a single eukaryotic cell is divided to form two daughter cells
What are microtubules?
globular tubulin proteins polymerise to form tubes that are used to form a scaffold-like structure that determines the shape of a cell
What do microtubules act as?
tracks for the movement of organelles, including vesicles, around the cell
What are spindle fibres composed of?
microtubles
What role do spindle fibres have?
a role in the physical segregation of chromosomes in cell division
What do intermediate fibres do?
give mechanical strength to cells and help maintain their integrity
What is integrity
the state of being whole and undivided.
what is segregation?
the separation of pairs of alleles at meiosis and their independent transmission via separate gametes.
The movement of cells like phagocytes depends on the activity of what?
actin filaments in the cytoskeleton
what are phagocytes
cells that protect the body by ingesting harmful foreign particles, bacteria, and dead or dying cells
When do the actin filament lengths in the cytoskeleton change?
with the addition and removal of monomer subunits
The rate at which these monomer subunits is added are what to each end of a filament for the filament lengths to change?
the rate at which these subunits are added is different at each end of a filament
Describe the subunits for the filament lengths to change?
not symmetrical and can be only added if they are in the correct orinetation
What do the subunits have to do befor they are added to one end (the minus end) of the filament but not the other end (the plus end)
they have to change shape
What does the subunits having to change shape befire they are added to one end of the filament for cell movement mean?
the subunits are added at a faster rate at the plus end
What dothe subunits being being added to the plus side faster therefore result in?
an increase in length at a faster rate in one particular direction
What are the subunits being added or removed at either end is determined by what?
the concentration of subunits in the cytoplasm
Due to the different rates of addition of subunits of filaments at either end, at certain concentrations…
what is this called
i) subunits will be added at one end and removed at the other
ii) treadmilling
What does the increasing length of the filaments at one edge of a cell, the leading edge, leads to?
cells such as phagocytes in a particular direction
What are centriules?
a component of the cytoskeleton present in most eukaryotic cells with the exception of flowering plants and most fungi
What are centrioles composed of?
microtubles
What do two associated centrioles form?
the centrosome
What is the form of the centrosome involved in?
two centrioles form the centrosome, which is invlolved in the assembly and organisation of the spindle fibres during cell division
In organisms with flagella cilia, what do centriules play a role in?
the positioning of the flagella and cilia
What is a similarity between flagella (whip-like) and cilia (hair-like)
they both are extensions that produce from some cell types
Flagella are ____ than cilia but cilia are usually present in much _____ numbers
i) longer
ii) greater
What are flagella primarily used for
to enable cells motility
what is motility?
the ability of organisms and fluid to move or get around
In some cells, what can flagella be used for?
used as a sensory orgonelle detecting chemical changes in the cells environement
Cilia can be ____ or statiionary
mobile
Stationary cilia are present where?
on the surface of many cells and have important function in sensory such as the nose
How do mobile cilia beat?
in a rhythmic manner, creating a current, abd cause fluids or objects adjacent to the cell to move
Give two examples of mobile cilia
1) they are present in the trachea to move mucus away from the lungs (helping tokeep the air passages clean)
2) fallopian tubes to move egg cells from the ovary to the uterus
What does each cillium contain?
two central microtubles (black circles) surrounded by nine pairs of microtubles arranged like a “wheel”
What are the nine pairs of microtubles arranged like a whell known as?
the 9+2 arrangement
What causes the mobile cilia to movie in a beating motion?
pairs of parallel microbules slide over each other
A key function of a cell is to synthesise proteins (including enzymes). What for?
internal use and for secretion (transport out of the cell)
A significant portion of what is required for secretion?
internal structure of the cell
What internal structures are closely linked and coordinate the production of proteins and their preparation for different roles within the cell
i) the ribosomes
ii) the endoplasmic reticulum
iii) golgi apparatus
The cytoskeleton plays a key role in coordinating what?
coordinating protein synthesis
What is the endoplasmic reticulym (ER)?
a network of membranes enclosing flattened sacs called cisternae
What is cisternae
flattened sacs
What is cisternae connected to ?
the outer membrane of the nucleus
What are the two types of endoplasmic reticulum
i) smooth endoplasmic reticulum
ii) rough endoplasmic reticulum
what is the smooth endoplasmic reticulum responsible for?
lipid and carbohydrate synthesis, and storage
what is the rough endoplasmic reticulum responsible for?
has ribosomes bound to the surface and is responsible for the synthesis and transport of proteins
What sort of cells have more rough endoplasmic reticulum than cells that do not release proteins?
secretory cells
Where are the ribosomes located?
it can be free-floating in the cytoplasm or attached to endoplasmic reticulum. forming rough endoplasmic reticulum
What are ribosomes not surrounded by?
a membrane
What are ribosomes constructed with and where?
RNA molecules made in the nucleolus of the cell
What are the site of protein synthesis
ribosomes
What also contains ribosomes other than being free floating inthe cytoplasm or attached to endoplasmic reticulum
mitochondria and chloroplasts, as do prokaryotic cells
What is the Golgi apparatus similar in strucutre to?
the smooth endoplasmic reticulum
What sort of structure of the Golgi appartus?
a compact structure formed of cisternae and does not contain ribosomes
What is the Golgi apparatus
an organelle in most eukaryotic cells formed from an interconnected network of flattened, membrane-enclosed sacs or cisternae
What does the Golgi apparatus play a role in?
modifying and packaging proteins into vesicles
What sort of vesicles could the Golgi appartus package?
secretory vesicles, if the proteins are destined to leave the cell, or lysosomes, which stay in the cell
Proteins are synthesised on what ribosomes?
on the ribosomes bound to the endoplasmic reticulum
After the proteins are synthesised on the ribosomes, what happens?
they are pass into a cisternae and are packaged into transport vesicles
Vesicles containing the newly synthesised proteins move towards the what and how?`
the Golgi apparatus via the transport function of the cytoskeleton
What do the vesicles fuse with while the proteins enter?
the vesicles fuse with the cis face of the Golgi apparatus
Describe the proteins before leaving the Golgi aparatus in vesicles from its trans face
structurally modified
Secretory vesicles carry proteins that are..
to be released from the cell
The secretory vesicles move towards and fuse with the what after they carriend the proteins that are ? and releasing what and how in the process?
with the cell surface membrane, releasing their contents by exocytosis
Some vesicles form what which contain enzymes for use in the cell?
lysosomes
Some vesicles form lysosomes. What do these contain?
enzymes for use in the cell
