Human bio

• 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
• what is each triplet of bases on an mRNA molecule

  a codon, which codes for a specific amino acid
• role of tRNA


  each transferRNA molecule carries its specific amino acid to the ribosome
• why does tRNA fold

  complementary base pairing
• structure of tRNA


  a tRNA molecule has an anticodon (an exposed triplet of bases) at one end and an attachment site for a specific amino acid at the other end
• role of rRNA


  ribosomal RNA and proteins form the ribosome
• the process of transcription involving RNA polymerase


  - RNA polymerase moves along DNA unwinding the double helix and breaking the hydrogen bonds between the bases

  - RNA polymerase synthesises a primary transcript of mRNA from RNA nucleotides by complementary base pairing
• what does RNA splicing do

  rna splicing forms a mature mRNA transcript
• process of RNA splicing

  - the introns (non-coding regions of DNA) are removed

  - the exons (coding regions of DNA) are retained and joined together to form the mature transcript, the order of exons is unchanged during splicing
• process of translation


  - tRNA is involved in the translation of mRNA into a polypeptide at a ribosome

  - translation begins at a start codon and ends at a stop codon

  - anticodons bond to codons by complementary base pairing, translating the genetic code into a sequence of amino acids

  - peptide bonds join the amino acids together

  - each tRNA then leaves the ribosome as the polypeptide is formed
• alternative RNA splicing


  different proteins can be expressed from one gene, as a result of alternative RNA splicing

  - different mature mRNA transcripts are produced from the same primary transcript depending on which exons are retained
• how is phenotype determined


  by proteins produced as the result of gene expression

  - environmental factors also affect phenotype
• how are amino acids linked

  amino acids are linked by peptide bonds to form polypeptides
• how do polypeptide chains becomes proteins, and how are they held together

  polypeptide chains fold to form the three-dimensional shape of a protein

  - held together by hydrogen bonds and other interactions between individual amino acids
• proteins have a large variety of shapes which determines their...

  functions
• what are mutations


  changes in the DNA that can result in no protein or an altered protein being synthesised