3.4 Eukaryotic cell structure Flashcards
What is the nucleus of a cell
How big is the nucleus
The nucleus is the most prominent feature of a eukaryotic cell, as it contains the organisms heriditary material and controls the cells activities
They are spherical and between 10qm and 20qm in diameter
The nucleus has 5 parts, name them
The nuclear envelope
Nuclear pores
Nucleoplasm
Chromosomes
The nucleolus
What is the nuclear envelope
(found in nucleus)
. It’s 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
. It controls the entry and exit of materials in and out of the nucleus and contains the reactions that take place within it
What are nuclear pores (found in nucleus)
How many are there in each nucleus and how big are they
. Allow the passage of large molecules such as messenger RNA out of the nucleus
. There are typically around 3000 pores in each nucleus, each 40-100nm in diameter
What is nucleoplasm
(found in nucleus)
Is the granular, jelly like material that makes up the bulk of the nucleus
What are chromosomes
(found in nucleus)
Consist of protein bound, linear DNA
What is the nucleolus
(found in the nucleus)
A 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 are the functions of the nucleus
. Act as a control centre of the cell through the production of mRNA and tRNA and hence protein synthesis
. Retain the genetic material of the cell in the form of DNA and chromosomes
. Manufacture ribosomal RNA and ribosomes
What is the size and shape of mitochondria
. They are rod shaped and are 1-10qm in length
A double membrane is found around the mitochondria, what does it do
What does the inner membrane do
. It controls the entry and exit of material
. The inner of the two membranes is folded to form extensions known as cristae
What are cristae and what do they do in mitochondria
. They are extensions of the inner membrane, which in some species extend across the whole width of the mitochondria
. They provide a large surface area for the attachment of enzymes and other proteins involved in respiration
What is the matrix in mitochondria
It makes up the remainder of the mitochondria
It contains protein, lipids, ribosomes, and DNA that allows the mitochondria to control the production of some of their own proteins
Many enzymes involved in respiration are found in the matrix
Why is the number of mitochondria in cells high
. They are the sites of the aerobic stages of respiration, so are responsible for the production of the energy carrying molecule ATP from respiratory substrates such as glucose
So the number of them are high in cells that have a high level of metabolic activity and therefore require a plentiful supply of ATP
Examples of metabolically active cells
Muscle and epithelial cells
Epithelial cells in the intestines require lots of ATP in the process of absorbing substances from the intestines by active transport
What are chloroplasts
How big are they
They are the organelles that carry out photosynthesis
They vary in shape and size but are typically disc shaped
They are 2-10qm long and 1qm in diameter
What are the 3 parts of chloroplasts called
The chloroplast envelope
The grana
The stroma
What does the chloroplast envelope do in chloroplasts
. It is a double plasma membrane that surrounds the organelle
. It is highly selective in what it allows to enter and leave the chloroplast
What is the grana found in chloroplasts
. They are stacks of up to 100 disc like structures called thylakoids
. Within the thylakoids is the photosynthetic pigment called chlorophyll
. Some thylakoids have tubular extensions that join up with thylakoids in adjacent grana
The grana are where the first stage of photosynthesis occurs (light absorption)
What is the stroma found in chloroplasts
Stroma is a fluid filled matrix where the second stage of photosynthesis occurs
(synthesis of sugars) and also protein synthesis
Within the stroma are a number of other structures such as starch grains
There are ribosomes found there
3 ways chloroplasts adapted to their function of harvesting sunlight and carrying out photosynthesis
- Granal membranes provide large surface area for the attachment of chlorophlyll, electron carriers and enzymes that carry out the first stage of photosynthesis.
These chemicals are attached to the membrane in a highly ordered fashion - The fluid of the stroma contains all of the enzymes needed to make sugars in the second stage of photosynthesis
- Chloroplasts contain both DNA and ribosomes so they can quickly and easily make some of the proteins needed for photosynthesis
What is the endoplasmic reticulum
It is an elaborate, 3D system of sheet like membranes, spreading through the cytoplasm of the cells.
It is continuous with the outer nuclear membrane
The membranes enclose a network of tubules and flattened sacs called cisternae
There are two types of endoplasmic reticulum
What is rough endoplasmic reticulum
. Has ribosomes present on the outer surfaces of the membranes: Its functions are to:
- Provide a large surface area for the protein synthesis
- Provide a pathway for the transport of materials, especially proteins, throughout the cell
There are two types of endoplasmic reticulum
What is smooth endoplasmic reticulum
. It lacks ribosomes on its surface and is even more tubular in appearance
Its functions:
- Sythesise, store and transport lipids
- Synthesise, store and transport carbohydrates
What cells store large quantities of ER
Cells that contain large quantities of carbohydrates, proteins and lipids.
Eg liver and secretory cells eg the epithelial cells that line the intestines
What is the Golgi apparatus and what is the structure
. Occurs in almost all eukaryotic cells and is similar to the SER in structure except it is more compact
. It consists of stacks of membranes that make up flattened sacs, or cisternae with small rounded hollow structures called vesicles
.
What happens when proteins and lipids are passed through the Golgi apparatus
. Proteins and lipids produced by the ER are passed through the Golgi apparatus in strict sequence
. The Golgi modifies these proteins often adding non protein components eg carbohydrates to form glycoproteins
. It also labels them so they can be accurately sorted and sent to the correct destinations
. Once sorted, the modified proteins and lipids 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
What are the functions of the Golgi apparatus
- Add carbohydrate to proteins to form glycoproteins
- Produce secretory enzymes
- Secrete carbohydrates such as cellulose used in making cell walls in plants
- Transport, modify and store lipids
- Form lysosomes
What are lysosomes and how are they formed
How big are they
Where are the found
- They are formed when the vesicles produced by the Golgi apparatus contain enzymes such as proteases and lipases
Lysosomes are 1qm in diameter
They are abundant in secretory cells eg epithelial cells and phagocytic cells
What do lysosomes contain
Lysozymes are enzymes that hydrolyse the cell walls of certain bacteria
- As many as 50 of these enzymes can be contained in a single lysosome
Lysosomes isolate these enzymes from the rest of the cell before releasing them, either to the outside or into a phagocytic vesicle within the cell.
What are the 4 functions of lysosomes
. Hydrolyse material injested by phogocytic cells, eg 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 the useful chemicals they are made of can be reused
. Completely break down cells after they have died (autolysis)
What are ribosomes, where are they found
Ribosomes are the site of in protein synthesis, so make proteins.
There are 2 stages of it (transcription and translation)
Ribosomes are small cytoplasmic granules found in all cells
They may occur in the cytoplasm or be associated with RER
There are 70s and 80s ribosomes
70s are found in mitochondria and chloroplasts
What are the two types of ribosomes and how big are they
. 80s: found in all eukaryotic cells, around 25nm in diameter
. 70s: Found in prokaryotic cells, mitochondria and chloroplasts , they are slightly smaller
What subunits do ribosomes have, what percentage of the dry mass of the cell do they make up
They have two sub units, one large and one small each of which containing ribosomal RNA and protein
Despite their small size, they occur in vast numbers so they account up for 25% of the dry mass of a cell
Why do mitochondria and chloroplasts contain 70s ribosomes
So they can make their own proteins eg enzymes for photosynthesis and respiration
What is the cell wall, what is it made of and why is this important for its function
Characteristic of all plant cells, cell walls consist of microfibrils of the polysaccharide cellulose, embedded in a matrix
Cellulose microfibrils have considerable strength so contribute to the overall strength of the cell wall
what features do cell walls have
What is lamella
. They consist of a number of polysaccharides eg cellulose
. There is a thin layer called the middle lamella which marks the boundary between adjacent cell walls together
What are the functions of the cellulose cell walls
. Provide mechanical strength in order to prevent the cell bursting under pressure. created by the osmotic entry of water
. Give mechanical strength to the plant as a whole
. Allow water to pass along it and so contribute to the movement of water through the plant
What are the cell walls of fungi made of
What are the cell walls of algae made of
. Cell walls of fungi contain a mixture of a nitrogen containing polysaccharide called chitin, a polysaccharide of glycan, and glycoproteins
Cell walls of algae are made of either cellulose or glycoproteins or a mixture of both
What is a vacuole, what is the membrane around it called
. A fluid filled sac bounded by a single membrane
. Within mature plant cells there is usually one large central vacuole
The single membrane around it is called the tonoplast
What do vacuoles contain
. Plant vacuole contains a solution of mineral salts, sugars, amino acids, wastes and sometimes pigments called anthocyanins
What functions do plant vacuoles have
. They support herbaceous plants, and herbaceous parts of woody plants by making cells turgid
. The sugars and amino acids may act as a temporary food store
. The pigments may colour petals to attract pollinating insects
How can you relate cell ultrastructure to function
. Each organelle has its own function, so you can find out the role of a cell by looking at the number and size of the organelles it contains
Eg as mitochondria produce ATP that is used as a temporary energy store, cells with many mitochondria are likely to require lots of ATP so therefore have a high rate of metabolism
How do Eukaryotic cells produce and release proteins.
DNA in nucleus is code (for protein)
Ribosomes/rough endoplasmic reticulum produce (protein)
Mitochondria produce ATP which provides the energy for protein synthesis
Golgi apparatus package/modify the proteins
Carbohydrate added/glycoprotein produced by Golgi apparatus
Vesicles transport or
Rough endoplasmic reticulum transports
(Vesicles) fuse with cell(-surface) membrane so exocytosis occurs
