eukaryotic cells structure and functions Flashcards
what are the functions of the nucleus?
-acts as the control centre of the cell through the production of mRNA and tRNA and hence protein synthesis
-retain genetic material of the cell in the form of DNA and chromosomes
-manufacture ribosomal RNA and ribosomes
what are the parts of the nucleus?
-nuclear envelope
-nuclear pores
-nucleoplasm
-chromosomes
-nucleolus
what is the nuclear envelope?
a double membrane that surrounds the nucleus
its outer membrane is continuous with the endoplasmic reticulum of the cell and often has ribosomes on its surface
what is the function of the nuclear envelope?
controls the entry and exit of materials in and out of the nucleus and contains the reactions taking place within it
what do nuclear pores do?
allow passage of large molecules, such as messenger RNA, out of the nucleus
how many nuclear pores are there typically in each nucleus?
3000, each 40-100nm in diameter
what is the nucleoplasm?
granular, jelly like material that makes up the bulk of the nucleus
what do chromosomes consist of?
protein bound, linear DNA
what is the nucleolus and what does it do?
small spherical region within the nucleoplasm- it manufactures ribosomal RNA and assembles the ribosomes.
There may be more than one nucleolus in a nucleus
what shape and size are mitochondria usually?
rod-shaped
1-10 micrometers in diameter
what surrounds the mitochondria?
a double membrane that controls the entry and exit of material
what happens to the inner membrane of mitochondria?
it is folded to form extensions known as cristae
what do cristae do in mitochondria?
they provide a large surface area for for the attachment of enzymes and other proteins involved in respiration eg ATP synthase
what is the matrix in mitochondria?
what makes up the remainder of the mitochondrion
it contains protein, lipids, ribosomes and DNA that allows the mitochondria to control the production of their own proteins
what else can be found in the matrix?
many enzymes involved in respiration
what are mitochondria the site of?
aerobic stages of respiration (the Krebs cycle and oxidative phosphorylation pathway)
what molecule is the mitochondria responsible for making?
the energy-carrier molecule ATP from respiratory substrates such as glucose
how are mitochondria effected in cells that require a plentiful supply of ATP due to the high metabolic activity in them?
the number and size of mitochondria will be high
number of cristae will be high
why do epithelial cells require a lot of ATP?
they require a lot of ATP in the process of absorbing substances from the intestines by active transport
what is the endoplasmic reticulum?
3D system of sheet-like membranes spreading through the cytoplasm. It is continuous with the outer nuclear membrane
what do the membranes of the ER do?
membranes enclose a network of tubules and flattened sacs called cisternae
what does the rough ER have on the surface?
ribosomes(for protein synthesis)
what are the functions of the rough ER?
-provide a large surface area for the synthesis of proteins by the ribosomes attached to the surface
-provide a pathway for the transport of materials, especially proteins, throughout the cell
what is the function of the smooth ER?
-synthesise, store and transport lipids
-synthesise, store and transport carbohydrates
what is the primary difference between the structures of the ER and golgi body?
The ER is a continuous network of sacs and tubules called cisternae, while the Golgi apparatus is made up of stacks of flattened sacs called cisternae
(connected vs not connected)
what is the structure of the golgi apparatus?
consists of a stack of membranes that make up flattened sacs , or cisternae, with small rounded hollow structures called vesicles
what happens to proteins and lipids produced in the ER?
passed through the Golgi apparatus in strict sequence. The Golgi modifies these proteins often adding non-protein components, such as carbohydrates to them
what else does the Golgi do to proteins and lipids, other than modifying them?
labels them- allowing them to be accurately sorted and sent to the right locations
once sorted, what happens to the modified proteins?
they are transported in Golgi vesicles which are regularly pinched off from the ends of the Golgi cisternae- these vesicles may move to the cell surface, where they fuse with the membrane and release their contents to the outside of the cell
what are the functions of the Golgi apparatus?
- protein, lipid and carbohydrate molecules produced in the ER are modified, stored and transported to the cell surface through secretory vesicles eg carbohydrate can be added to protein to produce glycoprotein
- form lysosomes
where might the Golgi apparatus be especially well developed?
in secretory cells, such as the epithelial cells that line the intestines
when are lysosomes formed?
when the vesicles produced by the Golgi apparatus contain enzymes such as proteases and lipases
what are lysozymes?
enzymes contained in the lysosomes that hydrolyse the cell walls of certain bacteria
what are the functions of lysosomes?
-hydrolyse material ingested by phagocytic cells, such as white blood cells and bacteria
-release enzymes to the outside of the cell (exocytosis) in order to destroy material around the cell
-digest worn out organelles so that the useful chemicals they are made of can be reused
-completely break down cells after they die (autolysis)
what is the role of ribosomes?
protein synthesis
which organelles are membrane bound?
-nucleus
-ER
- Golgi apparatus
-mitochondria
-lysosomes
-vesicles
compare DNA in the nucleus with DNA in mitochondria?
-DNA in the nucleus is linear whereas DNA in mitochondria is circular
-DNA in nucleus long and associated with proteins called histones whereas DNA in mitochondria is short and not associated with histones
in nuclear DNA, how is a chromosome formed?
together a DNA molecule and its associated proteins forms a chromosome
