U6-7- CELL ORGANISATION

MEIOSIS

MITOSIS

CELL CYCLE

CHROMOSOMES

CELL STRUCTURE

CELL THEORY

the cell, cell cycle and chromosomes

CELL THEORY

CELL THEORY

Components of cells

Eukaryotic

prokaryotic

cell types

eukaryotic cells

ROUGH

• Structure: ribosomes attached to the membrane
• Function: Protein synthesis and transport

SMOOTH

• Structure: without ribosomes
• Function: Lipid syntheis, storage and transport.

Endoplasmic reticulum

eukaryotic cells

• Structure: Series of unconnected flat sacs, surrounded by vesicles
• Function:
• Modifying substances synthesied by the ER
• Secreteng substances outside of the cell
• Moving substances within the cell

Golgi apparatus

eukaryotic cells

• Structure: Bean shape.
• They have two membranes: a smooth outer membrane and a highly folded inner one that forms cristae.
• They have an internal matrix containing ribosomes and small DNA molecules
• Function: In here cellular respiration takes place. In this process cells obtain energy from organic compounds.

mitochondria

eukaryotic cells

• Structure: Membrane extensions supported internally by the cytoskeleton.
• Cilia are short and abundant
• Flagella are long and few in number
• Function:
• Movement of the cell in aquatic environments
• Movement of the fluids outside of the cell

cilia and flagella

eukaryotic cells

• Structure: Rounded membranous vesicles containing many enzymes.
• More abundant in animal than in plant cells

• Function:
• Break down or digest substances, particles and organelles.

lysosome

eukaryotic cells

• Structure: Network of protein fibers and filaments that forms a scaffold or internal skeleton.
• Function: Gives shape to the cell and allows movement of the elements inside it.

cytoskeleton

eukaryotic cells

• Structure: Formed by two centrioles, hollow cylindrical structures arranged perpendicularly near the nucleus
• Not present in plant cells
• Function:
• cytoskeleton and microtubules for cell division emanate from here

centrosome

eukaryotic cells

Function:

• Perform photosysnthesis

Structure:

• Oval organelles exclusive of plant cells.
• They have a double membrane:
• Smooth outer membrane
• Folded inner one, forming tylakoids.
• It contains ribosomes and DNA molecules

Chloroplasts

eukaryotic cells

Function

• Storage of substances such as nutrientes or waste products.

Vacuoles

Structure

• Saccules surrounded by a single membrane
• They can occupy a large volume of the plant cell's cytoplasm:
• Large central vacuole: stores water

eukaryotic cells

Function

• Gives shape and rigidity to the cell
• Prevents the cell breaking

cell wall

Structure

• Thick, rigid covering surrounding the cell membrane of plant cells

Endosymbiotic theory

Lynn Margulis

origin of eukaryotic cells

the cell nucleus

• Nuclear envelope:
• Double membrane. The outer membrane has ribosomes attached and is continuous with the rough ER.
• Contains nuclear pores which enable the exchange of substances with the cytoplasm
• Surrounds and protects the nucleus
• Nucleoplasm: Aqueous medium inside the nucleus containing the other nuclear components
• Nucleolus:
• Not surrounded by a membrane.
• There can be one or more in different cells
• Ribosomes are formed in the nucleolus
• Chromatin:
• Formed by DNA molecules coiled tightly around proteins (histones).
• Euchromatin
• Heterochromatin
• Chromosomes are the maximum condensation of chromatin. Each chromosome is one DNA molecule.

structure of the nucleus

the cell nucleus

the cell cycle

Cell division (M phase)

• Shortest stage
• Mitotic division

cell cycle

Interphase (G1, S, G2)

• Longest stage: lasts from the end of one division to the start of the next.
• G1: Growth of the cell
• S: DNA replication
• G2: Cell prepares for cell division
• If the cell remains in interphase permanently it differenciates into a specilised cell (neurons, heart muscle cells, tec.)

the cHROMOSOME

• DNA molecule compacted (one single molecule or two copies of the same DNA molecule)
• Contain genetic information of the individual
• Transference of information from parent cells to daughter cells

the cHROMOSOME

• All individuals within a species have the same number of chromosomes (except their gametes that have half of them)
• Cells can be:
• Diploid: they have two sets of chromosomes
• Haploid: have only one set of chromosomes
• Homologous chromosomes:
• Determine the same biological characteristics, but the may have different information
• They are identical in shape and size
• Chromosome bands:
• Each chromosome produces unique bands
• Each band represents a segment of DNA containing many genes

Genetic diseases

the cHROMOSOME

• Karyotype: set of chromosomes in a cell or an organism
• Chromosomes can be:
• Autosomes: contain general information
• Sex chromosomes: determine the sex of the organism. in mammals these are chromosome X and Y.
• Karyotypes are used to diagnose genetic diseases

MITOSIS

CELL DIVISION

• Mitosis: division of the nucleus
• Equal distribution of the genetic materials between both daughter cells
• Functions:
• Asexual reproduction
• Growth and tissue repair

cytokinesis

CELL DIVISION

• Cytokinesis: division of the cytoplasm
• Cytoplams distributed between both daughter cells
• Animal cells: cleveage at the cell equator
• Plant cells: formation of a septum (called phragmoplasm) in the middle of the cell

second division

first division

BIOLOGICAL SIGNIFICANCE

• Production of gametes: esential for sexual reproduction
• Reduction of number of chromosomes in gametes (n): after fertilization zygote has a complete chromosome pool (2n)
• Increase the genetic variation of species due to the:
• genetic recombination between maternal and paternal homologous chromosomes resulting in new combinations of genetic material
• independent assortment of chromosomes resulting in gametes with random combinations of maternal and paternal chromosomes

meiosis

• Involves two consecutive cell divisions
• First: reductional
• Second: equational
• Results in four haploid (n) cells:
• Each one having half as many chromosomes as the parent cell
• All four cells are genetically different from each other

meiosis

mitosis vs meiosis