Summary Edexcel Biology AS Level (Salters Nuffield A) Topic 3 - Voice of the Genome - Full Notes
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Course
Topic 3 (9BNO01)
Institution
PEARSON (PEARSON)
Detailed and comprehensive notes on topic 3 (voice of the genome) of Edexcel biology AS Level. Covers eukaryotic/prokaryotic cell structure, protein transport, microscopy, cell organisation, gametes, fertilisation, meiosis, the cell cycle & mitosis, stem cells, differential gene expression, epigene...
Reproduction.......................................................................................................................................9-13
Gametes .................................................................................................................................................................................................................. 9
Fertilisation........................................................................................................................................................................................................ 10
Meiosis .......................................................................................................................................................................................................... 11-13
Crossing Over of Chromatids ........................................................................................................................................................................ 12
Independent Assortment of Chromosomes ............................................................................................................................................. 13
Linkage ................................................................................................................................................................................................................. 13
The Cell Cycle .................................................................................................................................... 14-15
The Cell Cycle .................................................................................................................................................................................................... 14
Mitosis .................................................................................................................................................................................................................. 15
Stem Cells and Differentiation ........................................................................................................... 16-20
Stem Cells ..................................................................................................................................................................................................... 16-18
Types of Stem Cells and Differentiation ................................................................................................................................................... 16
Plant Stem Cells and Therapeutic Cloning ............................................................................................................................................. 17
Stem Cells in Medicine and ISPCs ............................................................................................................................................................... 18
Differential Gene Expression (lac operon) .................................................................................................................................... 19-20
Variation ........................................................................................................................................... 21-23
Organisation of DNA ...................................................................................................................................................................................... 21
Epigenetics .................................................................................................................................................................................................. 22-23
Variation .............................................................................................................................................................................................................. 23
,Topic Checklist
3.1 Know that all living organisms are made of cells, sharing some common features. (P3)
3.2 Know the ultrastructure of eukaryotic cells, including nucleus, nucleolus, ribosomes, rough and smooth
endoplasmic reticulum, mitochondria, centrioles, lysosomes, and Golgi apparatus. (P3-4)
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. (P6)
3.4 Know the ultrastructure of prokaryotic cells, including cell wall, capsule, plasmid, flagellum, pili, ribosomes,
mesosomes and circular DNA. (P5)
3.5 Be able to recognise the organelles in 3.2 from electron microscope (EM) images. (P7)
3.6 Understand how mammalian gametes are specialised for their functions (including the acrosome in sperm and
the zona pellucida in the egg). (P9)
3.7 Know the process of fertilisation in mammals, including the acrosome reaction, the cortical reaction and the
fusion of nuclei. (P10)
3.8 i) Know that a locus (plural = loci) is the location of genes on a chromosome. (P13)
ii) Understand the linkage of genes on a chromosome and sex linkage. (P13)
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). (P11-13)
3.10 Understand the role of mitosis and the cell cycle in producing identical daughter cells for growth and asexual
reproduction. (P14-15)
3.11 i) Understand what is meant by the terms ‘stem cell, pluripotency and totipotency’. (P16)
ii) Be able to discuss the way society uses scientific knowledge to make decisions about the use of stem cells
in medical therapies. (P17-18)
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. (P19-20)
3.13 Understand how the cells of multicellular organisms are organised into tissues, tissues into organs and organs
into systems. (P8)
3.14 i) Understand how phenotype is the result of an interaction between genotype and the environment. (P23)
ii) Know how epigenetic changes, including DNA methylation and histone modification, can modify the
activation of certain genes. (P22)
iii) Understand how epigenetic changes can be passed on following cell division. (P23)
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. (P23)
Core Practical 5:
Prepare and stain a root tip squash to observe the stages of mitosis.
2
,Cells
All living organisms are made of cells and share some common features. Organisms can be prokaryotes or eukaryotes:
• Prokaryotic organisms are prokaryotic cells (i.e. they are unicellular organisms).
• Eukaryotic organisms are made up of eukaryotic cells.
Eukaryotic cells are complex and include all animal and plant cells. Prokaryotic cells are smaller and simpler.
Eukaryotic Cell Structure
3
, Eukaryotic Cell Structure
Organelles in Plant Cells and Animal Cells
Nucleus
• Double Nuclear Envelope – contains nuclear
pores to allow substances to pass through;
encloses and protects DNA.
• Nuclear Pores – allow substances to enter and
exit the nucleus; control what passes through.
• Nucleoplasm – contains chromatin granules of
DNA and proteins that condense during mitosis;
contains nucleoli.
• Nucleolus – dense body; produces ribosomes.
• Outer membrane continuous with rough
endoplasmic reticulum membranes –
perinuclear space continuous with lumen of
endoplasmic reticulum, allowing easy transport
of substances.
Ribosomes
• A small organelle that is not membrane-bound.
• Either floats free in the cytoplasm or attached to the rough endoplasmic reticulum.
• Produced in the nucleolus and made up of proteins and ribosomal RNA (rRNA).
• Composed of two subunits – a smaller subunit (where the mRNA codon binds to the tRNA anticodon) and the
larger subunit (where peptide bond formation occurs).
Golgi
• A group of fluid-filled, membrane-bound, flattened sacs.
• It processes new lipids and proteins and packages them in vesicles.
Rough Endoplasmic Reticulum (RER)
• A system of membranous tubules and flattened sacs enclosing a fluid-filled space.
• The surface is covered with ribosomes.
• Folds and processes proteins that have been made at the ribosome.
Smooth Endoplasmic Reticulum (SER)
• A system of membranous tubules and flattened sacs enclosing a fluid-filled space.
• The difference between the SER and the RER is that the SER has no ribosomes.
• Site of lipid and steroid metabolism, i.e. it synthesises triglycerides, cholesterol and phospholipids which
become part of the cell surface membrane.
Mitochondria
• Double Membrane – separates matrix from
cytoplasm; such high compartmentalisation allows
high concentrations of enzymes and substrates to be
maintained, which increases the rate of respiratory
reactions.
• Inner Membrane folds to from Cristae – greatly
increases the surface area for the attachment of
enzymes and co-enzymes involved in respiration.
• Matrix contains enzymes for respiration and DNA /
70S ribosomes for the transcription and translation of
proteins.
• The site of aerobic respiration where ATP is produced.
(See previous page for details on cell surface membrane, lysosome and centrioles).
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