human biology spec

• Types of cells that divide

  • Somatic stem cells
  • Germline stem cells
• Division of somatic cells

  Divide by mitosis to form more somatic cells
• Division of germline cells

  1. Divide by mitosis and by meiosis

  2. Division by mitosis produces more germline stem cells

  3. Division by meiosis produces haploid gametes
• Cellular differentiation

  The process by which a cell expresses certain genes to produce proteins characteristic for that type of cell, allowing the cell to carry out specialised functions
• Embryonic and tissue stem cells

  • Cells in the very early embryo can differentiate into all the cell types that make up the individual and so are pluripotent
  • Tissue stem cells are involved in the growth, repair and renewal of the cells found in that tissue and they are multipotent
• Therapeutic and research uses of stem cells

  • Therapeutic uses involve the repair of damaged or diseased organs or tissues
  • Research uses involve stem cells being used as model cells to study how diseases develop or being used for drug testing
• The ethical issues of using embryonic stem cells
• Cancer cells divide excessively because they do not respond to regulatory signals, resulting in a mass of abnormal cells called a tumour. Cells within the tumour may fail to attach to each other, spreading through the body where they may form secondary tumours
• DNA

  Nucleotides (deoxyribose sugar, phosphate and base), sugar–phosphate backbone, base pairing (adenine–thymine and guanine–cytosine) by hydrogen bonds and double stranded antiparallel structure, with deoxyribose and phosphate at 3' and 5' ends of each strand respectively, forming a double helix
• Replication of DNA

  1. DNA polymerase adds DNA nucleotides, using complementary base pairing, to the deoxyribose (3') end of the new DNA strand which is forming

  2. Fragments of DNA are joined together by ligase
• Polymerase chain reaction (PCR)

  1. Amplifies DNA using complementary primers for specific target sequences

  2. Repeated cycles of heating and cooling amplify the target region of DNA
• Practical applications of PCR
• Types of RNA involved in gene expression

  • Messenger RNA (mRNA)
  • Transfer RNA (tRNA)
  • Ribosomal RNA (rRNA)
• Transcription

  1. Role of RNA polymerase in transcribing DNA into primary mRNA transcripts

  2. RNA splicing forms a mature mRNA transcript by removing introns (non-coding regions) and joining exons (coding regions)
• Translation

  1. tRNA is involved in translating mRNA into a polypeptide at a ribosome

  2. Translation begins at a start codon and ends at a stop codon

  3. Anticodons bond to codons by complementary base pairing, translating the genetic code into a sequence of amino acids

  4. Peptide bonds join the amino acids together
• 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
• Polypeptide

  Amino acids are linked by peptide bonds to form polypeptides. 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
• Phenotype is determined by proteins produced as the result of gene expression
• Types of mutations

  • Single gene mutations (substitution, insertion or deletion of nucleotides)
  • Chromosome structure mutations (duplication, deletion, inversion and translocation)
• The substantial changes in chromosome mutations often make them lethal
• Genome

  The entire hereditary information encoded in DNA, made up of genes and other DNA sequences that do not code for proteins
• In genomic sequencing the sequence of nucleotide bases can be determined for individual genes and entire genomes
• An individual's genome can be analysed to predict the likelihood of developing certain diseases. Pharmacogenetics and personalised medicine
• Metabolic pathways

  Integrated and controlled pathways of enzyme-catalysed reactions within a cell, that can have reversible steps, irreversible steps and alternative routes. Reactions can be anabolic (building up large molecules) or catabolic (breaking down large molecules)
• Control of metabolic pathways

  • Presence or absence of particular enzymes
  • Regulation of the rate of reaction of key enzymes
  • Induced fit and the role of the active site of an enzyme in affecting activation energy and the affinity of the substrate and products for the active site
  • Effects of substrate and product concentration on the direction and rate of enzyme reactions
  • Competitive, non-competitive and feedback inhibition of enzymes
• Cellular respiration

  1. Glycolysis (breakdown of glucose to pyruvate in cytoplasm)

  2. Citric acid cycle (acetyl group from acetyl coenzyme A combines with oxaloacetate to form citrate, gradually converted back into oxaloacetate, generating ATP and releasing carbon dioxide)

  3. Electron transport chain (hydrogen ions and electrons from NADH passed along, releasing energy to pump hydrogen ions across inner mitochondrial membrane, flow back through ATP synthase results in ATP production, hydrogen ions and electrons combine with oxygen to form water)
• Role of ATP

  Transfer of energy
• Lactate metabolism

  1. During vigorous exercise, pyruvate is converted to lactate to regenerate NAD needed to maintain ATP production through glycolysis

  2. Lactate accumulates and muscle fatigue occurs

  3. Oxygen debt is repaid when exercise is complete, allowing respiration to convert lactate back to pyruvate and glucose in the liver
• Types of skeletal muscle fibres

  • Slow-twitch (contract relatively slowly, sustain contractions for longer, useful for endurance activities)
  • Fast-twitch (contract relatively quickly, over short periods, useful for activities such as sprinting or weightlifting)
• Most human muscle tissue contains a mixture of both slow- and fast-twitch muscle fibres. Athletes show distinct patterns of muscle fibres that reflect their sporting activities
• Gamete production in the testes

  1. Testes produce sperm in the seminiferous tubules and testosterone in the interstitial cells

  2. Prostate gland and seminal vesicles secrete fluids that maintain the mobility and viability of the sperm
• Gamete production in the ovaries

  Ovaries contain immature ova in various stages of development, each ovum surrounded by a follicle that protects the developing ovum and secretes hormones
• Fertilisation

  Mature ova are released into the oviduct where they may be fertilised by sperm to form a zygote
• Hormonal control of reproduction

  • Hormonal influence on puberty
  • Hormonal control of sperm production
  • Hormonal control of the menstrual cycle
• Hormonal control of the menstrual cycle

  1. FSH stimulates follicle development and oestrogen production in follicular phase

  2. Oestrogen stimulates endometrial proliferation and affects cervical mucus

  3. Peak oestrogen triggers LH surge which triggers ovulation

  4. In luteal phase, corpus luteum secretes progesterone to prepare endometrium for implantation

  5. Negative feedback of ovarian hormones prevents further follicle development, lack of LH leads to corpus luteum degeneration and menstruation
• Infertility treatments and contraception

  • Stimulating ovulation
  • Artificial insemination
  • Intra-cytoplasmic sperm injection (ICSI)
  • In vitro fertilisation (IVF)
  • Physical and chemical methods of contraception
• Stimulating ovulation

  1. Drugs that prevent negative feedback of oestrogen on FSH secretion

  2. Drugs that mimic FSH and LH action, can cause super ovulation
• Artificial insemination

  Several semen samples collected, used to inseminate woman, useful where male has low sperm count or uses donor sperm
• Intra-cytoplasmic sperm injection (ICSI)

  Sperm head injected directly into egg to achieve fertilisation, used where mature sperm are defective or very low in number
• In vitro fertilisation (IVF)

  Surgical removal of eggs from ovaries after hormone stimulation, incubation of zygotes and uterine implantation, used with pre-implantation genetic diagnosis (PGD) to identify disorders