Cells 2.1-2.2 Flashcards
Structure of eukaryotic cells
Cell surface membrane Nucleus Mitochondria Chloroplasts Golgi Apparatus and Golgi vesicles Lysosomes Ribosomes Rough and smooth endoplasmic reticulum Cell wall Cell vacuole
The nucleus structure
Nuclear envelope Nuclear pores Nucleoplasm Chromosomes Nucleolus
Nucleus’ functions
Act as the control centre of the cells 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
Nuclear envelope
A double membrane that surrounds the nucleus. It’s outer membrane is continuous with the endoplasmic reticulum of the cell and often has ribosomes on the surface. It controls the entry and exit of materials in and out of the nucleus and contains the reactions taking place within it
Nuclear pores
Allow the passage of large molecules, such as messenger RNA, out of the nucleus. There are typically around 3000 pores in each nucleus
Nucleoplasm
The granular, jellylike material that makes up the bulk of the nucleus
Chromosomes
Consist of protein-bound, linear DNA
Nucleolus
A small spherical region within the nucleoplasm. It manufactures ribosomal RNA and assembles the ribosomes. There may be more than one nucleolus in the nucleus
mitochondria’s structure
Double membrane
Cristae
Matrix
Mitochondria’s double membrane
Around the organelle is a double membrane that controls the entry and exit of material. The inner of the two membranes is folded to form extensions known as Cristae
Cristae
Are extensions of the inner membrane, which in some species extend across the whole width of the mitochondrion. These provide a large surface area for the attachment of enzymes and other proteins involved in respiration
Matrix
The matrix makes up the remainder of the mitochondrion. 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
Mitochondria’s function
Mitochondria are the sites of the aerobic stages of respiration
They are therefore responsible for the production of the energy carrier molecule, ATP, from respiratory substrates such as glucose. Because of this, the number and size of mitochondria, and the number of the Cristae, 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 include muscle and epithelial cells.
Chloroplasts structure
The chloroplast envelope The grana Thylakoids Chlorophyll The stroma
The chloroplast Envelope
A double plasma membrane that surrounds the organelle
It is highly selective in what it allows to enter and leave the chloroplast
The grana
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
Grana are where the first stage of photosynthesis (light absorption) takes place
The stroma
A fluid filled matrix where the second stage of photosynthesis (synthesis of sugars) takes place
Within the stroma are a number of other structures, such as grains
Chloroplast adaptions for 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 attach the membrane in a highly ordered fashion
The fluid of the stroma possesses all the enzymes needed to make sugars in the second stage of photosynthesis
Chloroplasts contain both DNA and ribosomes so they can quickly and easily manufacture some of the proteins needed for photosynthesis
Rough endoplasmic reticulum
Has ribosomes present on the outer surfaces of the membranes.
Endoplasmic reticulum
An elaborate, three-dimensional 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 ER
Smooth endoplasmic reticulum
Lacks ribosomes on its surface and is often more tubular in appearance
RER functions
Provide a large surface area for the synthesis of proteins and glycoproteins
Provide a new pathway for the transport of materials, especially proteins, throughout the cell
SER functions
Synthesise, store and transport lipids
Synthesise, store and transport carbohydrates
Golgi apparatus function
Add carbohydrate to proteins to form glycoproteins
Produce Secretary enzymes, such as those secreted by the pancreas
Secrete carbohydrates, such as those used in making cells walls in plants
Transport, modify and store lipids
Form lysosomes
Golgi apparatus sequence
The proteins and lipids produced by the ER are passed through the Golgi apparatus in strict sequence. The Golgi modifies proteins often adding nonprotein components such as carbohydrates to them
It also ‘labels’ them, allowing them to be accurately sorted and sent to the correct destinations
Once sorted, modified proteins and lipids are transported in Golgi vesicles
Lysosomes functions
Hydrolyse material ingested by phagocytic cells, such as white blood cells and bacteria
Release enzymes to the outside of the cell 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 have died
How are lysosomes formed
Formed when the vesicles produced by the Golgi apparatus contain enzymes such as proteases and lipases
Lysosomes are a type of Golgi vesicle that releases lysozymes
Ribosomes structure
Small cytoplasmic granules found in all cells
They may occur in the cytoplasm or be associated with the RER
Have two subunits – one large and one small – each of which contains ribosomal RNA and protein
Two types of ribosomes
80S – found in eukaryotic cells, is around 25 nm in diameter
70 S – found in prokaryotic cells, mitochondria and chloroplasts, is slightly smaller
Ribosomes function
Despite the small size, they are quite in such fast numbers that they can account for up to 25% of the dry mass of the cell
The site protein synthesis
Cell wall features
Consist of a number of polysaccharides, such as Celulose
There is a thin layer called the middle lamella, which marks the boundary between adjacent cells and cements adjacent cells together
Cell wall functions
Provide mechanical strength in order to prevent the cell busting 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 plants
Vacuoles functions
Support herbaceous plants, and herbaceous parts of woody plants, making cells turgid
Sugars and amino acids may act as a temporary food store
The pigments may colour petals to attract pollinating insects
Vacuoles structure
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
A plant vacuole contains a solution of mineral salts, sugars, amino acids, wastes and sometimes pigments
specialised cells
In complex multi cellular organisms, eukaryotic cells become specialised for specific functions
Specialised cells are organised into tissues, tissues into organs and organs into systems
Tissues
A collection of similar cells that perform a specific function are known as a tissue
Examples of tissues include
Epithelials tissues
Xylem
Epithelial tissues
Found in animals and consist of sheets of cells
They line the surface of organs and often have a protective or secretary function
There are many similar types, including those made up of thin, flat cells that line organs where diffusion takes place, for example the alveoli of the lungs, and ciliated epithelium that lines a duct such as the trachea
The cilia are used to move the mucus over the epithelial surface
