1. HOW MUCH DO YOU KNOW ABOUT CELLS?

Transcription

1 UNIT 3. THE CELL

2 1. HOW MUCH DO YOU KNOW ABOUT CELLS? 1. Watch a video and then answer the questions: - What is a cell? - Why the cell is a important structure?

3 1. HOW MUCH DO YOU KNOW ABOUT CELLS? 2. Look at the microscope photos and answer the questions - Are all the cells the same? - What do you think they have in common? - Try to classify the cells and explain what criterion you have used.

4 2. THE CELL odefinition: - Cells are the smallest unit of life - They are structural and functional units for all living thing ocellular THEORY: -All living things are made up of one or more cells -Cell carry out the functions of nutrition, interaction with the enviroment and reproduction -All cells come from other cells

5 3. THE ANATOMY OF A CELL Parts of a cell: The plasmatic membrane: is a thin strip made up of a double layer of phospholipids and proteins which separate the interior and the exterior of the cell. Functions: It is responsible for regulating the interchange of substances between the cellular interior and the exterior It protects the cell It distinguishes it from other cells. Vegetable cells also have a hard cellular wall of cellulose which covers the membrane.

6 3. THE ANATOMY OF A CELL Parts of a cell: The cytoplasm: is a jelly substance inside the cell. It is made up of a fluid, the hyaloplasm, which houses the cytoplasmatic organelles and a series of filaments of proteins which give the cell its shape, known as cytoskeleton. Numerous metabolic chemical reactions are produced in the hyaloplasm.

7 3. THE ANATOMY OF A CELL The cytoplasm: The most important organelles are the following: Ribosomes: Are spherical particles which consist of two different sized sub-unid which can be found in great number in the cytoplasm or associated to the membranes. These are the organelles which are responsible for the synthesis of proteins.

8 3. THE ANATOMY OF A CELL The cytoplasm: Endoplasmatic reticules: This is a set of membranes which limits cavities, tubes and cisterns which are intercommunicated with the plasmatic membrane and with the nuclear membrane. There are two types: Rough endoplasmatic reticule: close to the nucleus and in contact with the nuclear envelope. It has ribosomes attached to its membranes. Smooth endoplasmatic reticule: more distant from the nucleus and with no ribosomes. - Function: - The function of the endoplasmatic reticule is to transport substances, especially the proteins made by the ribosomes of the membrane

9 3. THE ANATOMY OF A CELL The cytoplasm: Golgi apparatus: This is made up of a series of vesibles which are piled onto each other, know as dictyosomes, surrounded by another series of vesicles which are smaller (secretion vesicles), formed from the dictyosomes themselves.

10 3. THE ANATOMY OF A CELL The cytoplasm: Mitochondria: These are long and ovoid in shape. They are limited by a double membrane, a flat exterior and an interior folds facing inwards known as mitochondrial crests. Between these there is a space known as the matrix. Responsible of cell respiration.

11 3. THE ANATOMY OF A CELL The cytoplasm: Chloroplasts: are formed by a double membrane: the exterior membrane is smooth and the interior membrane is in the form of flat sheets and sacks known as thylakoids. These sacks may be piled up to form grana. The chlorophyll is found in the membrane of the thylakoids. The interior space of the chloroplast is called stroma. Responsible for the photosynthesis

12 3. THE ANATOMY OF A CELL The cytoplasm: Vacuoles: These are reasonably large bags which are limited by a membrane and they accumulate reserve or waste sustances in their interior. The system of vacuoles is much more developed in vegetables cells than in animal cells.

13 3. THE ANATOMY OF A CELL The cytoplasm: Lysosomes: are a special type of vesicle which comes from the dictyosome, and they contain enzynes which are specialised in intracellular digestion. Centriole: this is an organelle which is exclusive to animal cell. It is a cylindrical structure, close to the nucleus, which intervenes in cellular division

14 3. THE ANATOMY OF A CELL The cytoplasm: Cilia and flagella: These are prolongations of the plasmatic membrane. Cilia: are numerous and short Flagella: are long and there are less of them They are related to cellular movement

15 3. THE ANATOMY OF A CELL Parts of a cell: The nucleus: This is the largest and most easily visible structure in a cell. It is surrounded by a nuclear membrane and its interior is taken up with a substance, the nucleoplasm, where the chromatin and the nucleole are inmersed. Parts: The nuclear membrane: is a double membrane and it is perforated by pores. It communicates with the rough endoplasmatic reticule. Its function is to regulate the interchange of substances between the nucleus and the cytoplasm Nucleole: This is spherical structure without a membrane formed by nucleic acid and proteins. Chromatin. Is an amorphous substance which takes up most of the nucleus. It is formed by DNA associated to proteins. These chains of DNA contain the genetic information of the cell. During cellular division, the chromatin condenses, forming structures which are shorter, thicker and more visible, the chromosomes.

16 4. TYPES OF CELL owe can different two basic types of cell: - Prokaryotic cells: - Are very simple and very small. - Don t have a defined nucleus, separated from the rest of the cell by a nuclear envelope - Don t have the majority of the cytoplasmatic organelles. - Only form single-celled organisms such as bacteria.

17 4. TYPES OF CELL - Eukaryotic cells: - Are more complex and bigger - Have a differentiated nucleus with a nuclear membrane which surrounds the genetic matter. - They can form single-celled and pluricellular organisms - We can distinguish two types of cell: animal and vegetable cell.

18 4. TYPES OF CELL - Animal and vegetable cell - Although their estructure and organisation is very similar, there are some diferrences betwen them: VEGETABLE CELL ANIMAL CELL - HAVE A CELLULAR WALL OF CELLULOSE WHICH COVER THE PLASMATIC MEMBRANE - ONLY HAVE A PLASMATIC MEMBRANE - HAVE PLAST IN THE CYTOPLASM - DON T HAVE PLASTS - HAVE A HIGHLY DEVELOPED SYSTEM OF VACUOLES - HAVE ONLY SMALL VACUOLES - DON T HAVE CENTRIOLES - HAVE CENTRIOLES

19 5. CELLULAR NUTRITION. METABOLISM Cells need energy to carry out their activities and matter to build their components. Cellular nutrition ensures the interchange of matter and energy between the cell and its enviroment. Cellular nutrition can happen in different ways, depending on the type of material and energy used: Heterotrophous: When organic and inorganic matter is incorporated. Use the chemical energy stored in the links of the organic material they incorporate. All animals, protozoa, fungi and many bacteria are made up heterotrophous cells. Autrotrophous: If only inorganic matter is incorporated. Use luminous energy which, by means of photosynthesis, they transform into chemical energy which they can use Green plant, cianobacteria and a significant group of bacteria are made up of autotrophous cells.

20 5. CELLULAR NUTRITION. METABOLISM Cellular nutrition has three phases: The entrance of matter and energy in the cell Transformation of matter and energy in the interior of the cell Exit of matter and energy to the external medium

21 5.1 THE INTERCHANGE OF SUBSTANCES The entrace and exit of matter in cells is controlled by the plasmatic membrane and can be done in various ways Osmosis: This is the normal way of interchange water. It passes from a less concentrated solution to a more concentrated one separated by a semipermeable membrane (like cellular membrane) which allow water to pass through but not the dissolved substances.

22 5.1 THE INTERCHANGE OF SUBSTANCES Diffusion: Small molecules which are soluble in water (mineral ions, O2, CO2) pass through the membrane plasmatic by diffusion from where there is greater concentration to where is less concentration. Facilitated diffusion: is the process of passive transport of molecules or ions across a cell membrane via specific transmembrane integral proteins. Facilitated transport does not involve the use of chemical energy; rather, molecules and ions move down their concentration gradient. Active transport: is the movement of molecules across a cell membrane against its concentration gradient (from low to high concentration). This transport requires energy and the participation of transporting proteins of the plasmatic membrane

23 5.1 THE INTERCHANGE OF SUBSTANCES

24 5.1 THE INTERCHANGE OF SUBSTANCES Endocytosis: is the process by which materials move into the cell. The cell s plasmatic membrane surrounds a macromolecule, liquid or even an entire cell from the extracellular environment and buds off to form a vesible. Exocytosis: materials are exported out of the cell via secretory vesicles. In this process, the Golgi complex packages macromolecules into transport vesicles that travel to and fuse with the plasmatic membrane. This fusion causes the vesicle to spill its contents out of the cell.

25 5.2 CELLULAR METABOLISM The matter and energy that enter the cells are subject to complex chemical transformation which are known as cellular metabolism. Cellular metabolism has two parts Catabolism: is the set of metabolic pathways that breaks down molecules into smaller units to release energy (ATP) Anabolism: is the set of metabolic pathways that construct molecules from smaller units. These reactions require energy (ATP).

26 6. THE INTERACTIVE FUNCTION IN A CELL Cells interact with the medium that surrounds them. Cells receive a series of stimuli (chemical, luminous, thermal ) which allows them to know the physical and chemical conditions of the external medium. Cells respond in accordance with the stimulus that they receive to ensure their survival. The responses of the cell may be very different and may manifest themselves in: changing of shape, movement, changes in metabolism, secretions

27 6. THE INTERACTIVE FUNCTION IN A CELL The movement responses are known as tactisms, which may be positive or negative depending on whether the cell goes towards or away from the stimulus. Cellular movement is made in three ways: pseudopods, flagella and cilia

28 6. CELLULAR REPRODUCTION By means of cellular reproduction, cell divide forming new cells. THE CELLULAR CYCLE It is the sequence of changes that occur in a cell from its formation until it divides giving rise to two daughter cells There are different phases: The interphase: is the phase in which the cell develops it normal activity. It grows until it reaches a specific size and DNA replication occurs. At the end of this process cell gets ready to divide. The phase of cellular division is the period in which the cell divides to from two daughter cells. Cellular division is known as mitosis and consists of two phases: Karyokinesis or the division of the nucleus Cytokinesis or the division of the cytoplasm

29 6. CELLULAR REPRODUCTION THE CELLULAR CYCLE

30 6.1 GENETIC MATERIAL AND CHROMOSOMES When the cell begins to divide a large number of transformations affect both the nucleus and the cytoplasm. The DNA which is found in a nucleus in interphase duplicates itself before beginning to divide. When the division is about to begin, the fibres of chromatin begin to fold in on themselves and are transformed into chromosomes. At the beginning of the division, the chromosomes are separated in two parts known as chromatids, joined together at a point known as the centromere.

31 6.1 GENETIC MATERIAL AND CHROMOSOMES The number of chromosomes of each species is always constant. (46 chromosomes in human species) In the majority of species this number is even (2n) and therefore they are known as diploid cells. This is because they posses two series of identical chromosomes in twos. The chromosomes of each pair are know as homologous. There are other cells which only have one series of chromosomes and, therefore, half the number (n); these cells are known as haploids. Generally, in species with diploid cells, the haploid cells are the gametes or reproductive cells which originate in sexual reproduction.

32 6.1 MITOSIS It is a conservative cellular division given that the daughter cells which are formed conserve the number of chromosomes and the genetic information of the mother cell. (Daughter cell are identical to each other and identical to the mother cell)

33 6.1 MITOSIS The first part of mitosis is Karyokinesis or the division of the nucleus. This stage has four phases: Prophase: Chromatin condenses into chromosomes. The centrioles begin to separate and emigrate to the poles of the cell. The nuclear membrane becomes disorganised and finally disappears. The nucleole disappear. Metaphase: The chromosomes are perfectly formed. The achromatic spindle appears which is a set of protein fibres which join the two centrioles. The chromosomes are at the centre of the cell (metaphase plate) The chromosomes are joined at the centromere to the spindle fibers

34 6.1 MITOSIS Anaphase: The chromosomes break at the centromere and divide into two sister chromatid. Each chromatid goes towards the opposite pole of the cell. Telophase: The emigration of the chromatid finishes. At each pole of the cell the chromatid begin to disappear. The nuclear membranes are formed of the two new nuclei The achromatic spindle appears The nucleole appear. Cytokinesis begins

35 6.1 MITOSIS Cytokinesis: This may be done in two ways Strangulation: A trough appears in the equatorial zone of the cell which gets bigger and bigger until it divides the cell in two. This is the way in which animal cells divide Partitioning: A plasmatic membrane is created in the equatorial zone which finally divides the cell in two. This form of division is typical of vegetable cells.

36 6.1 MITOSIS

37 6.2 MEIOSIS It is a very special division which can only be found in diploid cells and it is related with sexual reproduction. The result of meiosis is not only the creation of daughter cells but also the division of the genetic material, in such a way that from a mother diploid cell four haploid daughter cells appear (with half the number of chromosomes as the initial cell)

38 6.2 MEIOSIS Meiosis consists of two successive divisions. First meiotic division: separates homologous chromosomes Prophase I: The nuclear envelope disappears and the centrioles (located at the top and bottom of the nucleus) begin forming spindle fibres The chromosomes become visible The homologous chromosomes formed a tetrad and crossover take place (between two of the non-sister chromatids; the other two remain uncrossed) DNA is exchanged between homologous chromosomes in a process called recombination. Metaphase I: Tetrads ( that are joined to the achromatic spindle) align at the metaphase plate Anaphase I: Each chromosome goes towards the opposite pole of the cell Telophase I: Two daughters haploid cells are formed

39 6.2 MEIOSIS Second meiotic division: separates sister chromatids Prophase II Metaphase II Anaphase II Telophase II This is a normal mitosis, with no significant difference to that described previously. As a result of the meiosis, from one diploid cell, four haploid cells are formed which are all different from each other and different from the mother cell. Meiosis is an important source of genetic variety in organisms.

40 6.2 MEIOSIS