The animal eucaryotic cell Structure, organization and ... · •The plasma membrane separates the...
Transcript of The animal eucaryotic cell Structure, organization and ... · •The plasma membrane separates the...
Faculdade de Desporto, Universidade do Porto, 1º Ciclo, 1º Ano
2012_2013
BIOQUÍMICA E BIOLOGIA CELULAR
António Ascensão, José Magalhães
The animal eucaryotic cell
Structure, organization and function
Formation of Eu(karyon)tic aerobic cells
Prokaryotic vs Eukaryotic cells
Prokaryotic vs eukaryotic cells
Animal vs plant cells
The eu(karyon)tic cell components
Adapted from “Biologia celular e molecular”, 3th edition, Lidel, 1999
• The plasma membrane separates the cell from the environment!
• The fundamental structure of cell membranes is the amphipathic lipid bilayer!
• Various membrane proteins present in the different cell membranes give each membrane a specific function and identity!
The plasma membrane
• Separates cell from environment
• Form compartments allowing specialization
• Regulation of transport
• Detection of signals
• Cell-cell communication
• Cell identity
Cellular membrane functions
• Selectively permeable double membrane barrier containing pores
• Encloses jellylike nucleoplasm, which contains essential solutes
• Outer membrane is continuous with the rough ER and is studded with ribosomes
• Inner membrane is lined with the nuclear lamina, which maintains the shape of the nucleus
• Pore complex regulates transport of large molecules into and out of the nucleus
2 meters of human DNA fits into a nucleus that’s 0.000005 meters across!
Nucleus structure
• Dis$nguish prokaryotes from eukaryotes • Repository of gene$c material
• DNA replica$on, transcrip$on and RNA processing
• Nuclear envelop allows gene expression regulated by post transcrip$onal mechanisms (in prokaryotes mRNA is translated while transcrip$on is s$ll occurring)
• By limi$ng the access of selected proteins to gene$c material, nuclear envelope also provide opportuni$es for the control of gene expression at the level of transcrip$on (transcrip$on factors)
Nucleus structure
• Outer membrane is con$nuous with the ER • Space between inner and outer membrane is directly
connected with the lumen of the ER
• Outer membrane is similar to ER membranes with ribosomes
• Inner membrane contains specific protein of nucleus such as those that bind to nuclear lamina
• Inner and outer membranes are joined at nuclear pores complexes (responsible for selec$ve traffic of proteins and RNAs)
Nucleus structure
Nuclear composi$on and organiza$on
DNA plus histones = chroma$n (packed long DNA molecules)
Heterochroma$n -‐ periphery of the nucleus, higher density -‐DNA does not originate proteins Euchroma$n -‐ lower density, inside nucleus -‐ DNA originates proteins (ac$ve or inac$ve genes) Nucleolus Various number in cells Place of ribosome biosynthesis
nucleus is a double membrane bound organelle
Nucleus
Nucleus (nuclear envelope and nuclear pore)
Nucleus (lamina)
• Fibrous meshwork that provides structural support to the nucleus (composes by 60-‐80 kDa proteins called lamins, a class of intermediate filaments)
• Lamins bind to specific inner nuclear membrane
proteins such as emerin and lamin B receptor
• Also bind to chroma$n trough histones H2A and H2B and other chroma$n proteins
Nucleus (pores and lamina)
Transduc$on – a very simple cartoon
Mononucleated vs polynucleated cells
Some defini$ons and concepts
Gene DNA sequence transcribed into mRNA and protein Alelle Is one of different forms of a gene; different forms of a gene, which may give rise to different phenotypes Genome the total complement of genes in an organism or cell Chromosome a single, very long DNA helix on which thousands of genes are encoded Locus the region of the chromosome at which a par$cular gene is located
Telomere
Protects chromosome from destruc$on and incorrect replica$on …by capping (buffering) the end of chromosome Telomeres decrease at each cell division Senescence theory of telomeres Cancer preven$on
A piece of repe$$ve DNA (the same exact li]le sequence over and over again) that does not code for any proteins.
• Protein synthesis (about
half cell’s proteins are made here)
• Protein movement (trafficking)
• Protein “proofreading”
The rough endoplasmic reticulum
• Granules containing protein and rRNA
• Site of protein synthesis
• Free ribosomes synthesize soluble proteins
• Membrane-bound ribosomes synthesize proteins to be incorporated into membranes
Ribosomes
Main func$ons facilita$on of protein folding -‐ correct folding of newly-‐made proteins is made possible by several ER chaperones transport of synthesized proteins in sacs called cisternae inser$on of proteins into the ER membrane Disulfide bond forma$on and rearrangement: stabilize the ter$ary and quaternary structure of many proteins Loca$on an extended endomembrane system con$nuous with the nuclear envelope Structure extensive membrane network of cisternae (sac-‐like structures) held together by the cytoskeleton The func$ons vary greatly depending on the exact type and the type of cell in which it resides. Rough, smooth and sarcoplasma$c
ER (endoplasma$c re$culum)
Interconnected network of tubules, vesicles and cisternae
RER
Is studded with protein-‐manufacturing ribosomes giving it a "rough" appearance
Ribosomes only bind to the ER once it begins to synthesize a protein des$ned for sor$ng
Con$nuous with the outer layer of the nuclear envelope
Works in concert with the Golgi complex to target new proteins to their proper des$na$ons
SER
Synthesis of lipids and steroids, metabolism of carbohydrates, regula$on of calcium concentra$on,
drug detoxifica$on, a]achment of receptors on cell membrane proteins
Con$nuous with the outer layer of the nuclear envelope
SR
Special type of SER found in smooth and striated muscle
The only structural difference between SR and SER is the medley of protein they have
SER synthesizes molecules and the SR stores and pumps calcium ions
ER (endoplasma$c re$culum)
ER (endoplasma$c re$culum – protein trafiking)
Secretory pathway: rough ER – Golgi – secretory vesicles – cellular exterior
ER (endoplasma$c re$culum – protein sor$ng)
• Proteins destined for secretion or incorporation into ER, Golgi apparatus,
lysosomes or plasma membrane are initially targeted to the ER. Those
proteins synthesized in membrane-bound ribosomes are translocated to ER
while their translation is in progress.
• In contrast, proteins destined to remain in cytosol or to be incorporated into
the nucleus, mitochondria, chloroplasts, or peroxisomes are synthesized on
free ribosomes and released into the cytosol when translation is complete
ER (endoplasma$c re$culum – protein sor$ng)
ER (endoplasma$c re$culum – targe$ng and folding of proteins)
ER (endoplasma$c re$culum – targe$ng proteins -‐ role of chaps)
• Localized near the nucleus and ER
• Collection of flattened membrane-bound sacs (4 to 6)
• Each Golgi stacks has two distinct faces (cis - entry and trans - exit)
• Groups of small vesicles are associated with Golgi
• Carbohydrate synthesis
• Modifying, sorting and packaging station of macromolecules for secretion or delivery to other organelles
Golgi Apparatus
• Cell suicide (suicide is bad for cells, but good for us!)
• Recycling cellular components
• Digesting food or cellular invaders
• The lysosome is not found in plant cells
The lysossome functions
Lysossomes enzymatic “artillery” …
Pathways of degradation in lysossomes
Lysossomes in action …
• Major site of O2 utilization in cell
• Vestige of an ancient organelle that carried out all of the oxygen metabolism in primitive ancestors of eukaryotic cells
• Contain enzymes (urate oxidase and catalase) that use molecular O2 to detoxify organic substrates producing H2O2
• Catalase uses this H2O2 to oxidize other substrates (ex: alchool in liver)
• When H2O2 accumulates catalase converts it to water
• Involved in β-oxidation (fatty acids to acetyl CoA)
Peroxissomes
Are you all seeing this ??
Mitochondria is not like this at all !!
Mitochondria
• Powerhouses of the cell
• Osmotic regulators
• Regulators of cell calcium homeostasis
• Activators of the intrinsic pathway of apoptosis
• Owns DNA for protein synthesis
Mitochondria structure and functions
Mitochondria structure and functions
Mitochondria structure and functions
Adapted from “Understanden human anatomy and physiology”, 5fh Edition, McGraw-Hill, 2004
General functions of cellular components
Video “cell organelles” (~6 min)
1- O aparecimento do oxigénio na atmosfera não condicionou a eficiência metabólica da vida na terra.
2- As células procarióticas possuem um núcleo bem delimitado por um sistema de dupla membrana, são maiores e possuem
organelos.
3- A incorporação de bactérias anaeróbias em céllulas eucarióticas ancestrais num processo de endosimbiose foi determinante
para evolução das células eucarióticas capazes de utilizar oxigénio.
4- O núcleo das células eucarióticas permite a regulação da expressão genética por mecanismos postranslacionais
5- Heterocromatina é uma zona periférica e densa do núcleo
6- A Eucormatina é uma zona interna e pouco densa do núcleo
7- O ER liso é um local de síntese de lípidos enquanto que os ribossomas livres sintetizam proteínas solúveis
8- O ER rugoso não está associado à síntese, maturação, dobragem, formatação e transporte de proteínas
9- Os lisossomas são organelos associados à degradação de detritos celulares e contêm enzimas (hidrolases) que actuam em
meio ácido.
10- As mitocôndrias têm como única função celular a produção de energia
11- São sub estruturas celulares importantes: membrana plasmática, citoesqueleto, núcleo, ER, Golgi, lisossomas, peroxissomas,
mitocôndrias.
12- A formação de lisossomas podem acontecer por mecanismos de endocitose, fagocitose e autofagia