Skip to Main Content

Chapter 10: Genetics & Disease

1. PURPOSE

  1. Genetics alone is a relatively small part of Step 1 but shows up as part of questions in almost every organ system

  2. The cell cycle provides an important foundation to discuss genetics, as cell division errors lead to diseases like Down syndrome

  3. Here we'll review some important concepts that can get easy points on Step 1

  4. We also review important genetic diseases seen in previous chapters to highlight how genetics can show up in many organ systems

  5. Lysosomal storage diseases represent a final review of genetics and review of concepts discussed previously

2. CELL CYCLE

  1. The cell cycle describes the common process of cell growth

  2. Phases can be divided into 3 main groups

  3. DNA Synthesis (S)

    1. The initial step toward cell division is replication of the DNA

    2. Each of the 23 pairs of chromosomes is duplicated, forming sister chromatids

  4. Mitosis/meiosis (M)

    1. After DNA synthesis and a period of rest, cells undergo division, and sister chromatids split to provide DNA for both daughter cells

    2. Germ cells meant for sexual reproduction undergo meiosis to produce gametes (sperm or ova)

    3. All other cells are somatic cells and undergo mitosis

  5. Gap/rest (G)

    1. G1: After recent division, the cell rests and carries out normal function

    2. G0: At this point the cell may enter a long-term rest phase if it does not need to regularly multiply

    3. G2: Between S and M phases, the cell grows and prepares organelles to support 2 new cells

    4. After M phase, the cell enters G1 and restarts the cycle, or may enter G0

Figure 10-1.

Overview of the cell cycle.

An illustration shows the G subscript 0, G subscript 1, S, G subscript 2, and mitosis phases of the cell cycle. This illustration is represented by a cyclic structure consisting of G subscript 1 phase, S phase, G subscript 2 phase, and mitosis, Two arrows arise from either ends of the G subscript 1 phase and taper outward to a cell structure. This is the G subscript 0 phase. Cell structures with chromosomes at different levels of rest, growth, or multiplication are shown across each phase of the cycle, with one representation for each phase. At G subscript zero, the cell shows the same structure as it does in G subscript 1 but slightly smaller, indicating that it is not multiplying or growing. The cell has three sets of chromatids present against a mesh-like background of the nucleus. The cell structure in G subscript 1 is similar to that in G subscript 0 but the size of the chromatids is slightly larger. In S phase, an additional chromatid is seen for each of the three chromatids, resulting in the cell having three chromosomes inside the nucleus. In G subscript 2, the cell structure is similar to that in S phase, but the size of all the three chromosomes are slightly larger. In mitosis, the cell is shown to be in the process of dividing into two parts. The nucleus is not present in both the poles of the structure that is dividing into two cells. Instead a centromere is present on either poles. Three dashed lines appear to arise from each of the centromeres. These dashed lines pass through the corresponding 6 chromatids that are now split into two sets of three each. The caption reads, “overview of the cell cycle.”
View Full Size||Download Slide (.ppt)

3. CELL CYCLE REGULATION

  1. The cell cycle is a crucial process that requires careful regulation

  2. Loss of regulation is a key mechanism underlying cancer

  3. There are 3 major types of regulation to discuss

    1. Cyclins

    2. Tumor suppressors

    3. Proto-oncogenes

4. CYCLINS

  1. Checkpoints at each step in the cycle prevent unrestrained cell division

  2. The 2 protein classes to know are cyclins and cyclin-dependent kinases

  3. Cyclins are the “time keepers” of the cell cycle

    1. Cyclin concentration changes depending on the phase of the cycle

    2. High levels of active cyclins are required to activate the next step of cell division

  4. Cyclin-dependent kinases (CDKs)

    1. Kinase proteins that are inactive in their resting state

    2. Binding of cyclins is required to activate CDKs and drive cell maturation

    3. However, cyclin binding is not sufficient to activate CDKs: Phosphorylation of the CDK is also required

  5. Phosphorylation of CDK-cyclin complexes allows for many checks on cell cycle progression

5. TUMOR SUPPRESSORS

  1. Many proteins that regulate the cell cycle were discovered because they are inactivated in cancer cells

  2. Tumor suppressors are a class of genes that work to limit cell ...

Pop-up div Successfully Displayed

This div only appears when the trigger link is hovered over. Otherwise it is hidden from view.

This site uses cookies to provide, maintain and improve your experience. MH Privacy Center Close