U1 KA 1-4

• what is a somatic cell


  any cell in the body other than cells involved in reproduction
• what are germline cells

  gametes (sperm and ova) and the stem cells that divide to form gametes
• somatic stem cells divide by ___________ to form ____________

  somatic stem cells divide by MITOSIS to form MORE SOMATIC CELLS
• germline stem cells divide by _________ and by __________

  germline stem cells divide by MITOSIS and by MEIOSIS
• division of germline stem cells by mitosis produces...

  more germline stem cells
• division of germline stem cells by meiosis produces...

  haploid gametes
• what are diploid cells

  cells that have 23 pairs of homologous chromosomes
• why do germline stem cells divide by mitosis

  to maintain the diploid chromosome number
• meiosis process


  - the nucleus of a germline stem cell can divide by meiosis

  - it undergoes two divisions, firstly separating homologous chromosomes and secondly separating chromatids
• what are haploid cells

  haploid gametes contain 23 single chromosomes
• what is cellular differentiation


  the process by which a cell expresses certain genes to produce proteins characteristic for that type of cell

  - this allows a cell to carry out specialised functions
• describe embryonic stem cells and how they can differentiate

  - pluripotent

  - cells in the very early embryo can differentiate into all the cell types that make up the individual

  - all the genes in embryonic stem cells can be switched on so these cells can differentiate into any type of cell
• what are tissue stem cells involved in

  the growth, repair and renewal of the cells found in that tissue
• how are tissue stem cells more limited

  - multipotent

  - can differentiate into all of the types of cell found in a particular tissue type.

  - for example, blood stem cells located in bone marrow can give rise to red blood cells, platelets, phagocytes and lymphocytes
• therapeutic uses of stem cells

  therapeutic uses involve the repair of damaged or diseased organs or tissues

  - used in corneal repair

  - used in regeneration of damahed skin

  - stem cells from embryo can self-renew, under the right conditions, in the lab
• research uses of stem cells


  involves stem cells being used as model cells to study how diseases develop or being used for drug testing

  - stem cell research provides information on how cell processes such as cell growth, differentiation and gene regulation work
• ethical concerns with using embryonic stem cells

  use of embryonic stem cells can offer effective treatments for disease and injury; however, it involves destruction of embryos
• what are cancer cells

  cells that divide excessively because they do not respond to regulatory signals, resulting in a mass of abnormal cells called a tumour
• how do secondary tumours form

  cells within a tumour may fail to attach to each other, spreading through the body where they may form secondary tumours
• what does the base sequence of DNA form

  the genetic code
• structure of DNA nucleotides

  - a 5 carbon deoxyribose sugar, a phosphate group (attached to 5' end) and a base (attached to the 1' end)
• how do the two strands of DNA run and what is the shape?

  in an antiparallel structure

  - with deoxyribose and phosphate at 3' and 5' ends of each strand respectively, forming a double helix
• DNA bases and pairing rules

  adenine pairs with thymine

  cytosine pairs with guanine
• how are the two DNA strands held together

  weak hydrogen bonds between complementary base pairs
• what is a primer


  a short strand of nucleotides which binds to the 3' end of the template DNA strand allowing DNA polymerase to add DNA nucleotides
• how does DNA polymerase add nucleotides?

  using complementary base pairing, to the deoxyribose (3') end of the new DNA strand which is forming
• process of DNA replication

  - DNA is unwound and hydrogen bonds between bases are broken to form two template strands

  - DNA polymerase can only add DNA nucleotides in one direction resulting in the leading strand being replicated continuously and the lagging strand replicated in fragments

  - ligase is used to join the fragmets together
• what does DNA polymerase do and require?

  - DNA is replicated by DNA polymerase prior to cell division

  - it requires primers
• what is PCR


  polymerase chain reaction (PCR) amplifies DNA using complementary primers for specific target sequences
• what are primers in PCR


  primers are short strands of nucleotides which are complementary to specific target sequences at the two ends of the region of DNA to be amplified
• what are the 3 stages of PCR

  heating, annealing, extension
• what do repeated cycles of heating and cooling do in PCR

  amplify the target region of DNA
• what happens in heating stage of PCR

  STAGE 1

  DNA is heated to between 92 and 98°C to separate the strands
• what happens in the annealing stage of PCR

  STAGE 2

  DNA is then cooled to between 50 and 65°C to allow primers to bind to target sequences
• what happens in the extension stage of PCR

  STAGE 3

  DNA is then heated to between 70 and 80°C for heat-tolerant DNA polymerase to replicate the region of DNA
• what are the practical applications of PCR

  PCR can amplify DNA to help solve crimes, settle paternity suits and diagnose genetic disorders
• are many genes in a cell expressed

  no, only a fraction of the genes in a cell are expressed
• differences between DNA and RNA

  DNA has deoyribose, thymine, and is double-stranded

  RNA has ribose, uracil, and is single-stranded
• role of mRNA


  messenger RNA carries a copy of the DNA code from the nucleus to the ribosome

  - mRNA is transcribed from DNA in the nucleus and translated into proteins by ribosomes in the cytoplasm

  - each triplet of bases on the mRNA molecule is called a codon and codes for a specific amino acid
• how is mRNA involved in transcription and translation


  mRNA is transcribed from DNA in the nucleus and translated into proteins by ribosomes in the cytoplasm