SNAB topic 3

• 3.1 Know that all living organisms are made of cells, sharing some common

  features.

  All living things are made of cells and share some common features:

  
  

  In multicellular organisms:

  Cells-->Tissues-->organs-->systems, each specified for a particular function(s)
• 3.2 Nucleus


  Double membrane (nuclear envelope) with nuclear pores

  Contains DNA, wrapped around histone proteins

  Contains a nucleolus
• 3.2 80s ribosomes


  Composed of two subunits

  
  

  Site of protein synthesis
• 3.2 Lysosomes


  Vesicles containing digestive enzymes

  
  

  Bound by a single membrane
• 3.2 Mitochondria


  Oval shaped, bound by a double membrane

  
  

  Inner membrane folds, forming cristae

  
  

  Contains enzyme for aerobic respiration
• 3.2 Golgi apparatus


  Series of fluid filled, flattened and curved sacs

  Vesicles surrounding edges

  Modifies and packagesproteins and lipids

  Produces lysosomes
• 3.2 Smooth ER


  System of membrane bound sacs

  Produces andprocesses lipids
• 3.2 Centrioles


  Perpendicular cylinders of microtubules

  
  

  Involved in cell division
• 3.2 Rough ER


  Series of flattened sacs, enclosed by a membrane

  Ribosomes attached to the surface

  Folds and processes proteinsmade on the ribosomes
• 3.3 Understand the role of the rough endoplasmic reticulum (rER) and the Golgi apparatus in protein transport within cells, including their role in the formation of extracellular enzymes.

  
• 3.4 Know the ultrastructure of prokaryotic cells, including cell wall, capsule, plasmid, flagellum, pili, ribosomes, mesosomes and circular DNA.

  
• 3.5 Be able to recognise the organelles in 3.2 from electron microscope (EM) images.


  Circle with blob=nucleusSmall bubbles=vesiclesOval/circle with pattern=mitochondriaLong, flattened darker lines near nucleus=ER
• 3.6 Understand how mammalian gametes are specialised for their functions (including the acrosome in sperm and the zona pellucida in the egg).


  Ovum:-Zona pellucida, protective jelly like coating, prevents polyspermy-Haploid nucleus-Cortical granules, releasing enzymes that harden the zona pellucida-Follicle cells form a protective coating around the egg.

  Sperm cell-Many mitochondria to make energy for flagellum-Acrosomes contain digestive enzymes that break down the zona pellucida
• 3.7 Know the process of fertilisation in mammals, including the acrosome reaction, the cortical reaction and the fusion of nuclei.

  
• 3.8 i) Know that a locus (plural = loci) is the location of genes on a chromosome.


  a locus is the location of genes on a chromosome.
• 3.8 ii) Understand the linkage of genes on a chromosome and sex linkage.


  Alleles on the same chromosomes=autosomally linked

  -> Thecloser the loci of the alleles,themore likely they are inherited together(they are less likely to be separated during DNA exchange during meiosis)

  Some genes are sex-linked because they only occur on the X-chromosomeand not on the Y chromosome.

  This meanssome genetic disorders are more likelyto occur in men, as they only need one recessive allele to express characteristics.
• 3.9 Understand the role of meiosis in ensuring genetic variation through the production of non-identical gametes as a consequence of independent assortment of chromosomes and crossing over of alleles between chromatids (details of the stages of meiosis are not required).

  Crossing overExchange of sections of DNA between homologous chromosomes

  (homologous= a pair of two chromosomes)

  Independent assortmentDifferent pairs of alleles separate from each other separately. Like shuffling a deck

  ( random combinations of ways that maternal and paternal chromosomes can be arranged in daughter cells of meiosis.)
• 3.10 Understand the role of mitosis and the cell cycle in producing identical daughter cells for growth and asexual reproduction.


  Cell cycle:Mitosis : prophase (condense), metaphase lined up), anaphase (pulled apart), telophase (nuclear envelopes reforming)

  Cytokinesis: cytoplasm divides, membrane splits off a new genetically identical cell

  Interphase:G1-Growth of cell and DNA replicationS- chromosomes are replicated and begin to condenseG2- organelles replicate
• CORE PRACTICAL 5:

  Prepare and stain a root tip squash to observe the stages of mitosis.


  Equipment•Root tip•Sharp knife•Acetic alcohol•HCl acid•Ice cold distilled water•Water bath at 60̊C•Test tube•Microscope, slides•Mounted needle•Toluidine blue stain

  Method1)Cut small piece of root tip2) The root tip needs to be macerated•Place test tube of HCl in water bath, leave to heat•Place root tip in alcohol for 10 mins•Remove tip, place in ice cold water for a few mins.•Place tip in heated HCl for a few mins.•Repeat this

  3) Break the tip with the mounted needle4) Prepare slide, add dye (blot out excess dye) view at 100x - 400x magnification.5) Count number of cells in one frame. Count the number of cells with visible chromosomes, in the same frame.

  CalculationCalculate the mitotic index:Mitotic index=Number of cells with chromosomes/Total number of cells
• 3.11 i) Understand what is meant by the terms 'stem cell, pluripotency and

  totipotency'.

  Stem cells are undifferentiated cells that can divide into new stem cells or develop into specialised cells

  Pluripotent:Can give rise to many types of specialised cellsbut not placental cells

  TotipotentCan give rise to all types of specialised cells
• 3.11 ii) Be able to discuss the way society uses scientific knowledge to make

  decisions about the use of stem cells in medical therapies.

  They can replace damaged tissue such as nerve tissue in spinal cord injuries.

  
  

  Some believe it is unethical as embryos are killed in the process

  
  

  There is a risk of infection when cells are transplanted.

  
  

  They could become cancerous.

  
  

  They could be rejected.
• 3.12 Understand how cells become specialised through differential gene expression, producing active mRNA leading to synthesis of proteins, which in turn control cell processes or determine cell structure in animals and plants, including the lac operon.

  Differential gene expressionStimulusacts on unspecialised cellsActivator/repressor molecules bind to promoter regionsSome genes are switched on.RNA polymerase can attach to active genes-Active genes are transcribedand translation occurs.The protein that is made canchange the structure and functionof the cellThe cell can become specialised

  Lac operonWhen lactose is present, the repressor molecule is unable to bind to the promoter/operator region.RNA polymerase can attach to DNA.B-galactosidase enzyme is made, can now break down lactose.
• 3.13 Understand how the cells of multicellular organisms are organised into tissues, tissues into organs and organs into systems.


  Cells of multicellular organisms are organised into tissues, tissues into organs and organs into systems.
• 3.14 i) Understand how phenotype is the result of an interaction between genotype and the environment.

  Phenotype is the result of an interaction between genotype and the environment.
• 3.14 ii) Know how epigenetic changes, including DNA methylation and histone modification, can modify the activation of certain genes.

  
  

  i made a small mistake (cant edit it) DNA methylation can both promote and prevent transcription


  DNA methylationMethyl group attaches to DNA,prevents transcription

  Histone modificationAffects how tightly DNA is wrapped around histone proteins.Tighter wrap=less available for transcription

  Histone acetylationpromotes transcriptionby making the DNA more accessible
• 3.14 iii) Understand how epigenetic changes can be passed on following cell division.

  Epigenetic changes are copied with the DNA before mitosis/meiosis and are passed down to daughter cell(s)
• 3.15 Understand how some phenotypes are affected by multiple alleles for the same gene at many loci (polygenic inheritance) as well as the environment and how this can give rise to phenotypes that show continuous variation.

  Combination of genotype and environmentl

  lung cancer: genetic predisposition + smoking increases risk

  height: polygenic characteristic, but can be limited due to environmental factors like deficiencies.Continuous variation

  animal hair colour:Some animals get darker fur at lower/higher temperaturesDiscrete variation