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