Unit 1 human biology

• Somatic cells


  Any cell within the body apart from reproductive cells
• Somatic cells


  • They are diploid therefore have 23 pairs of homologous chromosomes
  • They divide by mitosis
• Germline cells


  Gametes (sperm and egg) and the stem cells that divide to form gametes
• Germline cells


  • They divide by mitosis to form diploid germline stem cells and meiosis to produce haploid cells
  • The nucleus of germline stem cell divides by mitosis to maintain diploid chromosome
  • Nucleus of germline stem cells divides by meiosis, first separating homologous chromosomes, then separating chromatids
  • Haploid gametes contain 23 single chromosomes
• Cellular differentiation


  Process by which a cell expresses certain genes to produce protein characteristics for that type of cell
• Embryonic stem cells


  Pluripotent, all genes switched on in the cells of very early embryos and thus can differentiate into any cell
• Tissue stem cells


  Involved in the growth, repair, and renewal of cells found in that tissue, multipotent, can differentiate into all cells found in a particular tissue type
• Tissue stem cells


  • E.g. blood stem cells found in the bone marrow give rise to red blood cells, platelets, phagocytes, and lymphocytes
• Therapeutic uses of stem cells

  Involved in the repair of damaged or diseased organs and tissue
• Therapeutic uses of stem cells

  • Cornea repair, regeneration of damaged skin
• Research uses of stem cells

  Stem cells from an embryo self-renew under the right conditions in a lab, used as model cells to study how diseases develop or used for drug testing, provide information on how cell processes work such as cell growth, differentiation, gene regulation work
• The use of embryonic stem cells can offer effective treatments for disease and injury however it involves the destruction of embryos which raises particular ethical issues
• Cancer cells


  Divide excessively because they do not respond to regulatory signals, results in a mass of abnormal cells called a tumour, cells within a tumour may fail to attach and spread through the body to form secondary tumours
• DNA structure


  Nucleotides consisting of deoxyribose sugar, phosphate and a base, a sugar-phosphate backbone held together by strong sugar-phosphate bonds, base pairing consisting of adenine-thymine, and guanine-cytoside, these are held together by weak hydrogen bonds, Double-stranded and antiparallel structure, deoxyribose and phosphate at the 3' and 5' ends of each strand respectively forming a double helix
• The base sequence of DNA


  Forms the genetic code
• Replication of DNA by DNA polymerase and primers

  DNA replicated before cell division by DNA polymerase, DNA polymerase needs primers to start the process of DNA replication, Primer is a short strand of nucleotides that bind to the 3' end of the template DNA strand allowing the polymerase to add DNA nucleotides, DNA polymerase adds DNA nucleotides using CBP to deoxyribose, 3' end, of newly formed DNA strand
• DNA replication process


  DNA unwound and hydrogen bonds between bases are broken forming 2 template strands, DNA primers binds to the 3' end of template DNA, DNA polymerase adds DNA nucleotides using CBP in one direction, of 3'end of new DNA, resulting in the leading strand being replicated continuously and the lagging strand replicated in fragments, DNA ligase joins all fragments of lagging strands together
• Polymerase chain reaction (PCR)

  Amplifies DNA using complementary primers of specific target sequences, Primers in PCR are short strands of nucleotides which are complementary to specific target sequences at the two ends of the region of DNA to be amplified, Repeated cycles of heating and cooling amplify the target region of DNA
• Practical application of PCR

  • Can amplify DNA to help solve crimes, settle paternity tests and diagnose genetic disorders
• Polymerase chain reaction process


  DNA heated to between 92 – 98 to separate the strands, Then cooled to between 50 – 65 to allow primers to bind to target sequences, Re-heated to between 70 – 80 for heat-tolerant DNA polymerase to replicate the region of DNA
• Gene expression


  Involves 2 stages: transcription (DNA to mRNA) and translation (MRNA to protein), Only a fraction of genes in any cell are expressed
• RNA


  Is single-stranded and is composed of nucleotides, Contains ribose sugar, phosphate and base, Bases are cytosine-guanine, adenine-uracil, three forms of RNA are involved in transcription and translation: messenger RNA (mRNA), transfer RNA (tRNA), ribosomal RNA (rRNA)
• Messenger RNA (mRNA)


  Carries a copy of the genetic 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 an mRNA strand is called a codon and codes for specific amino acids
• Transfer RNA (tRNA)


  Each tRNA molecule carries its specific amino acid to the ribosome, tRNA has an anticodon (an exposed triplet of bases) at one end and an attachment site for a specific amino acid at the other end, tRNA folds due to complementary base pairing
• Ribosomal RNA (rRNA)


  Forms the ribosome along with proteins, the ribosome is a complex structure that moves along the mRNA strand matching specific tRNA molecules
• Transcription


  Process by which a copy of DNA is made and occurs in the nucleus, copy is known as mRNA
• Transcription stages


  RNA polymerase moves along gene/DNA unwinding the double helix and breaking the hydrogen bonds between bases, RNA polymerase synthesis a primary transcript of mRNA from free RNA nucleotides by CBP
• RNA splicing


  Primary mRNA transcript has both coding (exons) and non coding (introns) region, Non coding regions (introns) are removed whilst coding regions(exons) are joined together to form a mature transcript, Order of exons remains unchanged during splicing
• Alternative RNA splicing


  Different proteins can be expressed from one gene as a result of alternative RNA splicing, Different mature mRNA transcripts produced from the same primary transcript depending on which exons are retained
• 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 end codon
• Translation stages


  Mature mRNA transcript attaches to ribosome in the cytoplasm, Start codon signals starting point of protein synthesis (translation), Complementary tRNA anticodons bond to codons on mRNA strand by CBP. Translating the genetic code into a sequence of amino acids, Peptide bonds join amino acids together, each tRNA molecule leaves a ribosome as the polypeptide chain is formed, Translation ends at the stop codon
• Proteins


  Amino acids are linked by peptide bonds to form polypeptides (proteins), Polypeptide chains fold to form 3D 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
• Phenotypes


  Phenotype is determined by proteins produced as a result of gene expression, Phenotype is a physical characteristic, Environmental factors also influence phenotype
• Mutations


  Mutations are changes in the DNA that can result in no protein or an altered protein being synthesized
• Single gene mutation


  Involves the alteration of a DNA nucleotide sequence because of substitution (a single nucleotide is replaced with a different nucleotide), insertion (a single nucleotide is added to a DNA sequence), or deletion (a single nucleotide is removed from a DNA sequence)
• Nucleotide substitutions


  Missense (an amino acid is changed for another, results in a non-functional protein or has little effect on the protein), Nonsense (results in a premature stop codon being produced which results in a shorter protein), Splice-site (results in some introns being retained or some exons not being included in the mature transcript)
• Nucleotide insertions and deletions

  Result in frameshift mutations, Frameshift (causes all codons and all amino acids after the mutation to be changed, has major effects on the structure of the protein produced)
• Chromosome structure mutations


  4 types: Duplication (a section of a chromosome is added from it homologous pair), Deletion (section of chromosome is removed), Inversion (section of chromosome is reversed), Translocation (section of a chromosome is added to a chromosome not its homologous pair), The substantial changes in chromosome mutations often make them lethal
• Nonsense mutation


  Results in a premature stop codon being produced which results in a shorter protein
• Splice-site mutation


  Results in some introns being retained or some exons not being included in the mature transcript