Cell structure and specialisation Flashcards
Describe the function of the nucleus
Act as the 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 ribosomes and ribosomal RNA
What are the five structures within the nucleus
Nuclear envelope
Nuclear pores
Chromosomes
Nucleoplasm
Nucleolus
What is the nuclear envelope and what does it do
The nuclear envelope is 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 taking place within it.
Describe the role of the nuclear pores
Nuclear pores allow the passage of large molecules such as mRNA out of the nucleus. There are typically around 3,000 pores in each nucleus, each 40-100 nm in diameter.
What are chromosomes
Chromosomes are molecules that contain protein bound, linear DNA.
What is the nucleoplasm
The nucleoplasm is the granular, jelly-like substance that makes up the bulk of the nucleus.
What is the nucleolus
The nucleolus is 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 three structures within the mitochondrion
Double membrane
Cristae
Matrix
What is the role of the double membrane that surrounds the mitochondrion
Each mitochondrion organelle is surrounded by a double membrane that controls the entry and exit of materials. The inner of the two membranes is folded to form extensions known as cristae.
What are the cristae (mitochondria)
Cristae are extensions of the inner membrane (in some species they extend across the whole width of the mitochondrion)
What do the cristae (mitochondria) do
Provide a large surface area for the attachment of enzymes and other proteins involved in respiration.
What is the matrix (mitochondria) and what is its function?
The matrix makes up the resort of the mitochondrion (thats not cristae or double membrane). It contains protein, lipid, 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.
What is the role of the mitochondria
Mitochondria are the sites of the aerobic stages of respiration- they are therefore responsible for the production of ATP from respiratory substrates such as glucose.
What are the three structures within the chloroplasts
The chloroplast envelope
The grana (and thylakoids)
The stroma
What is the chloroplast envelope
The chloroplast envelope is a double plasma membrane that surrounds the organelle. It is highly selective in what it allows to enter and leave the chloroplast.
What are the grana and thylakoids (chloroplasts)
Thylakoids are disc-like structures that contain the chlorophyll needed to absorb light in the first stage of photosynthesis. The grana are stacks of the disc-shaped thylakoids.
What is the stroma (chloroplasts) and what is its role
The stroma is a fluid filled matrix within the chloroplasts where the second stage of photosynthesis (synthesis of sugars) takes place.
Describe how chloroplasts are adapted to their function of harvesting sunlight and carrying out photosynthesis
The granal membranes provide a large surface area for the attachment of chlorophyll, electron
carriers and enzymes that carry out the first stage of photosynthesis. These chemicals are attached to the membrane in a very ordered fashion.
The fluid of the stroma possesses the enzymes needed to make sugars in the second phase of photosynthesis.
Chloroplasts contain both DNA and ribosomes so that they can quickly and easily manufacture some of the proteins needed for photosynthesis.
Describe the endoplasmic reticulum
The endoplasmic reticulum is an elaborate, three-dimensional system of sheet-like membranes that spreads through the cytoplasm of the cells. It is continuous with the outer nuclear membrane and the membranes enclose a network of tubules and flattened sacs called cisternae.
What are the two types of endoplasmic reticulum
The rough endoplasmic reticulum
The smooth endoplasmic reticulum
What is the rough endoplasmic reticulum and what is its function
The rough endoplasmic reticulum has ribosomes on its surface.
It’s function is to provide a large surface area for the synthesis of proteins and glycoproteins and to provide a pathway for the transport of materials (especially proteins) throughout the cell.
What is the smooth endoplasmic reticulum and what is its function
The smooth endoplasmic reticulum does not have ribosomes on its surface and is more tubular in appearance. Its function is to synthesise, store and transport lipids and carbohydrates.
What is the Golgi apparatus
The Golgi apparatus consists of a stack of membranes that make up flattened sacs, or cisternae, with small rounded hollow structures called vesicles.
Describe what happens in the Golgi apparatus
The proteins and lipids produced by the endoplasmic reticulum are passed through the Golgi apparatus in strict sequence. The Golgi modifies these proteins and often adds non-protein components to them.
It also ‘labels’ them, allowing proteins to be accurately sorted and sent to their correct destinations. Once sorted, the modified proteins and lipids are transported in Golgi vesicles which are regularly pinched off from the ends of Golgi cisternae.
These vesicles may move to the cell surface where they fuse with the membrane and release their contents to the outside.
List the functions of the Golgi apparatus
Add carbohydrates to proteins to form glycoproteins
Produce secretory enzymes
Secrete carbohydrates, such as those used in making cell walls in plants.
Transport, modify and store lipids
Form lysosomes
What are lysosomes
Lysosomes are formed when the vesicles produced by the Golgi apparatus contain enzymes such as proteases and lipases. They also contain lysozymes- enzymes that hydrolyse the cell walls of certain bacteria.
List the functions of the 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 re-used.
Completely break down cells after they have died (autolysis)
What is the function of ribosomes
Protein synthesis
Describe the structure of ribosomes
Ribosomes are small cytoplasmic granules found in cells. They may occur in the cytoplasm or be associated with the rough endoplasmic reticulum. The type of ribosomes present depends on what type of cell it is. Ribosomes have two subunits (one large and one small), each of which contains ribosomal RNA and proteins.
What are 80S ribosomes
The ribosomes found in eukaryotic cells and they are around 25nm in diameter.
What are 70s ribosomes
The ribosomes found in prokaryotic cells, mitochondria and chloroplasts. 70S ribosomes are much smaller than 80S ribosomes.
Describe the structure of a plant cell wall.
Cell walls consist of microfibrils of the polysaccharide cellulose embedded in a matrix.
They consist of many polysaccharides such as cellulose.
There is a thin layer called the middle lamella which forms the boundary between adjacent cell walls and cements adjacent cells together.
List the functions of a cellulose cell wall
To provide mechanical strength in order to prevent the cell from bursting under the pressure created by the osmotic entry of water.
To give mechanical strength to the plant as a whole.
To allow water to pass along it and so contribute to the movement of water through the plant.
What are the cell walls of algae made up of
Cellulose, glycoproteins, or a mixture of both.
What are the cell walls of fungi made of
The cell walls of fungi do not contain cellulose but comprise of a mixture of a nitrogen-containing polysaccharide called chitin, a polysaccharide called glycan and glycoproteins.
What is a vacuole and what is its structure
A vacuole is a fluid filled sac bound by a single membrane.
In mature plants, there is usually one large central vacuole although a cell can have more than one vacuole.
The single membrane around it is called the tonoplast.
A plant vacuole contains a solution of mineral salts, sugars, amino acids, wastes and sometimes more/others.
List the functions of a plant vacuole
They support herbaceous plants, and herbaceous parts of woody plants by making cells turgid.
The sugars and amino acids stored in it act as a temporary food store.
The pigments may colour petals to attract pollinating insects.
What types of cells contain an extensive endoplasmic reticulum
Cells that manufacture and store large quantities of carbohydrates, proteins and lipids. This includes cells such as liver cells, and epithelial cells that line the intestines.
What types of cells have a well developed Golgi apparatus
Secretory cells such as the epithelial cells that line the intestines.
What types of cell have many lysosomes
Secretory cells such as phagocytic cells and epithelial cells.
List the sub-cellular structures that can be found in eukaryotic cells
Nucleus
Mitochondria
Chloroplasts
Endoplasmic reticulum (smooth and rough)
Golgi apparatus
Ribosomes
Cell wall
Vacuoles
List the sub-cellular structures that can be found in prokaryotic cells
Ribosomes
Cell membrane
Circular loop of DNA
Plasmids
Flagellum
Cytoplasm
Cell wall
Slime capsule
What is a slime capsule and what is its function
A slime capsule is a mucilaginous layer of slime (only found in certain species) that protects bacterium from other cells and helps groups of bacteria stick together for further protection.
Describe a bacterial cell wall
A bacterial cell wall is 10-80nm thick and made of murein. It is a physical barrier that excludes certain substances and protects against mechanical damage and osmotic lysis.
What is a flagellum
A ‘tail’ found in some prokaryotic cells that is used for locomotion. There may be more than one (flagella)
What is the cytoplasm of a cell
The jelly-like substance found in a cell. It contains enzymes and other soluble materials.
What are plasmids and what is their function
Plasmids are small,circular pieces of DNA found in certain bacterial species. They contain the genetic material/genes that may aid the survival of bacteria in adverse conditions.
What is the circular DNA in prokaryotic cells
A loop of DNA that possesses the genetic information for the replication of bacterial cells.
Summarise the role of a cell surface membrane
To act as a differential permeable layer around the outside of the cell that controls the entry and exit of chemicals.
Compare the nucleus’ and DNA in prokaryotic and eukaryotic cells
In prokaryotic cells there is no true nucleus, only an area where DNA is found whereas eukaryotic cells have a distinct nucleus with a nuclear envelope.
Prokaryotic DNA is not associated with proteins whereas eukaryotic DNA is associated with proteins called histones.
In prokaryotic cells, some DNA may be in the form of circular strands called plasmids but in eukaryotic cells there are no plasmids and DNA is linear.
Compare how organelles are found in prokaryotic and eukaryotic cells
In prokaryotic cells, there are no membrane-bound organelles. In eukaryotic cells, membrane bound organelles such as mitochondria are present.
Compare the difference in chloroplasts between prokaryotic and eukaryotic cells.
There are no chloroplasts in prokaryotic cells, but in some bacteria there is bacterial chlorophyll associated with the cell-surface membrane. In eukaryotic cells, chloroplasts are found in plants and algae.
Compare the difference in ribosomes in prokaryotic and eukaryotic cells
70S ribosomes are found in prokaryotic cells which are smaller than the larger 80S ribosomes found in eukaryotic cells.
Compare the difference in cell walls between eukaryotic and prokaryotic cells
The cell walls in prokaryotic cells are made of murein (peptidoglycan) but where present in eukaryotic cells, the cell walls are made of cellulose (in plants) or chitin (fungi)
Compare the outer layers of prokaryotic and eukaryotic cells
Prokaryotic cells may have an outer mucilaginous layer called a capsule but eukaryotic cells have no capsule.
List key comparison points between prokaryotic and eukaryotic cells
DNA and nucleus’
Organelles-membrane bound or not
Chloroplasts/chlorophyll
Sub-cellular structures present
Type of ribosomes
Difference in cell walls
Outer capsule/no outer capsule.
How do cells become specialised? (When they all have the same DNA)
Every cell contains the genes needed for it to develop into any one of the many different cells in an organism. However, only some of these genes are switched on (expressed) in anyone cell, at any one time. Different genes are switched on in each type of specialised cell and others are switched off.
What varies in a cell when it becomes specialised
The cells shape and its organelles.
What is a tissue
A group of similar specialised cells working together to carry out a specific function.
What are epithelial tissues
Tissues found in animals that consist of sheets of cells. They line the surface of organs and often have a protective or secretory function. There are many different types including ones consisting of thin, flat cells that line the surface of organs where diffusion takes place.
What are some examples of epithelial tissues
Alveoli of the lungs, ciliated epithelium that lines a duct such as the trachea.
What is an organ
A group of different specialised tissues that work together to carry out a specific function
Why are arteries and veins organs but capillaries aren’t
Both arteries and veins are made up of a variety of different tissues whereas capillaries are only made up a epithelial tissues so are not organs.
What is an organ system
A group of organs working together to carry out a key metabolic process such as respiration, digestion and circulation.
