bio

• Label the cell:

  A) lysosome

  B) mitochondria

  C) cytoplasm

  D) ribosomes

  E) plasma membrane

  F) nucleus

  G) nuclear membrane

  H) pore in nuclear membrane

  
• two stem cells:

  • embryonic = pluripotent (potential for all genes turned on)
  • tissue = multipotent (narrow differentiation potential)
• Explain why red blood cells contain haemoglobin after differentiation but white blood cells do not?

  genes coding for haemoglobin in the red blood cell are switched on/expressed, but off/not expressed in the white blood cell
• suggest how stem cells may repair damaged organs?

  stem cells are cultured in laboratory then transplanted into damaged area
• meiosis is to produce haploid gametes
• Describe what is meant by cellular differentiation?

  the process a cell develops more specialised functions by expressing the genes characteristics for that type of cell
• A DNA nucleotide consists of 3 components:

  • deoxyribose sugar
  • phosphate
  • base
• Prior to cell division, DNA is replicated by DNA Polymerase.
• DNA Polymerase needs PRIMERS to start replication.
• A Primer is a short strand of nucleotides which binds to the 3’ end of the template DNA strand allowing the DNA Polymerase to add DNA Nucleotides.
• DNA is unwound (by DNA Polymerase) and Hydrogen bonds between the bases are broken to form 2 template strands.
• DNA Polymerase adds DNA Nucleotides, using complimentary base pairing, to the deoxyribose (3’) end of the new DNA strand which is forming.
• DNA Polymerase can only add DNA Nucleotides in one direction, resulting in the Leading Strand being replicated continuously and the Lagging Strand being replicated in Fragments.
• Fragments of DNA on the Lagging strand are joined together by LIGASE.
• PCR AMPLIFIES DNA using complimentary primers for specific target sequences
• Repeated cycles of HEATING & COOLING amplify the target region of DNA.
• In PCR, primers are short strands of nucleotides which are complimentary to specific target sequences at the 2 ends of the region of DNA to be amplified.
• PCR TEMPERATURES:

  • DNA is heated to between 92 and 98 C to separate the strands.
  • It is then cooled to between 50 and 65 C to allow Primers to bind to target sequences.
  • It is then heated to between 70 and 80 C for HEAT-TOLERANT DNA Polymerase to replicate the region of DNA
  • cycle is then repeated
• PCR requires:

  1. A DNA Template
  2. A Supply of the 4 types of DNA Nucleotides (A,T,C &G)
  3. Primers
  4. Heat-tolerant DNA Polymerase (enzyme)
  5. A pH Buffer ( to create optimum conditions for enzyme activity)
• PCR can amplify DNA for use in the following applications:

  1. To help SOLVE CRIMES ( Forensic evidence).
  2. Settle PATERNITY SUITS
  3. Diagnose Genetic Disorders.
• Gene Expression involves the transcription and translation of DNA sequences. Only a fraction of the genes in a cell are expressed.
• Transcription and translation involves 3 types of RNA: mRNA, tRNA and rRNA.
• RNA is single stranded and is composed of nucleotides containing Ribose sugar, phosphate and 1 of 4 bases:

  • Cytosine
  • Guanine
  • Adenine
  • Uracil (there is no Thymine in RNA, Uracil replaces this).
• Messenger RNA (mRNA) carries a copy of the DNA code from the nucleus to the Ribosome.
• Each triplet of bases on the mRNA molecule is called a CODON and codes for a specific amino acid.
• tRNA folds due to complementary base pairing. Each tRNA molecule carries its specific amino acid to the ribosome
• 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.
• Ribosomal RNA (rRNA) and Proteins are used to form the Ribosome.
• TRANSCRIPTION:

  The enzyme RNA POLYMERASE moves along DNA UNWINDING the double helix and breaking the hydrogen bonds between the bases.
• TRANSCRIPTION:

  RNA Polymerase synthesises a PRIMARY mRNA TRANSCRIPT from RNA Nucleotides by complimentary base pairing
• Uracil in RNA is complimentary to Adenine
• RNA SPLICING:

  Some of the DNA which is transcribed (copied) is NON-CODING (does not contain the information required to produce a protein) and therefore these regions known as INTRONS must be removed from the Primary mRNA Transcript.
• Clue : NICE (Non-coding Introns, Coding Exons)
• RNA Splicing involves the removal of the NON-CODING INTRONS and joining together (Splicing) of the CODING regions known as EXONS.
• The order of Exons is UNCHANGED during Splicing.
• ALTERNATIVE RNA SPLICING:

  Different Proteins can be expressed from ONE GENE as a result of Alternative RNA Splicing.
• Amino Acids are linked by PEPTIDE BONDS to form POLYPEPTIDES.
• Polypeptide Chains FOLD to form the 3-Dimentional shape of a Protein, held together by HYDROGEN BONDS and other interactions between individual amino acids.
• Phenotype is determined by the proteins produced as the result of Gene Expression.
• Environmental factors also influence phenotype.