Unit 1 Cell Biology

Unit Introduction

Welcome to the Cell Biology Unit...or as we like to call it, What are we made of? In this unit we take your understanding of all things cellular and go a lot deeper. You'll find out how cells are made, what cells are really made of and, more importantly, what all their structures actually do.

As you'll know by now, cells are the basic structures of all living things, and therefore understanding them is crucial for understanding life. Did you know there are about 10 trillion human cells in our body, and another 90 trillion bacteria cells on and in your body! That's a lot of cells reading this webpage!

Learning Outcomes

    • Cell ultrastructure and functions to include: cell walls, mitochondria, chloroplasts, cell membrane, vacuole, nucleus, ribosomes, plasmids; using examples from typical plant, animal, fungi and bacteria cells.

    • The cell membrane consists of lipids and proteins and is selectively permeable.

    • Passive transport is with the concentration gradient and does not require energy.

    • The importance of diffusion in cells as the movement of molecules along a concentration gradient.

    • Osmosis as the movement of water molecules across a membrane in terms of water concentration.

    • Animal cells can burst or shrink and plant cells can become turgid or plasmolysed in different solutions.

    • Active transport requires energy for membrane proteins to move molecules against the concentration gradient.

    • Maintenance of diploid chromosome complement by mitosis.

    • Sequence of events of mitosis, including equator and spindle fibres.

    • Cell production by cell culture requires aseptic techniques, an appropriate medium and the control of other factors.

    • Structure of DNA: double-stranded helix held by complementary base pairs.

    • DNA carries the genetic information for making proteins. The four bases A, T, C and G make up the genetic code. The base sequence determines amino acid sequence in protein.

    • Messenger RNA (mRNA) is a molecule which carries a copy of the code from the DNA, in the nucleus, to a ribosome, where the protein is assembled from amino acids.

    • The variety of protein shapes and functions arises from the sequence of amino acids.

    • Functions of proteins to include structural, enzymes, hormones, antibodies.

    • Enzymes function as biological catalysts and are made by all living cells.

      • They speed up cellular reactions and are unchanged in the process.

      • The shape of the active site of enzyme molecules is complementary to a specific substrate.

      • Each enzyme works best in its optimum conditions.

      • Enzymes and other proteins can be affected by temperature and pH, which result in changes in their shape.

      • A change in shape will affect the rate of reaction and may result in denaturation.

    • Genetic information can be transferred from one cell to another naturally or by genetic engineering.

    • Stages of genetic engineering to include:

      • identify section of DNA that contains required gene from source chromosome,

      • extract required gene,

      • insert required gene into vector/bacterial plasmid,

      • insert plasmid into host cell,

      • grow transformed cells to produce a GM organism.

    • Chemistry of photosynthesis, as a series of enzyme-controlled reactions, in a two-stage process.

      • Light reactions:

        • The light energy from the sun is trapped by chlorophyll in the chloroplasts and is converted into chemical energy in the form of ATP.

        • Water is split to produce hydrogen and oxygen.

        • Excess oxygen diffuses from the cell.

      • Carbon fixation:

        • Hydrogen and ATP produced by the light reaction is used with carbon dioxide to produce sugar.

    • The chemical energy in sugar is available for respiration or can be converted into plant products such as starch and cellulose.

    • Limiting factors: carbon dioxide concentration, light intensity and temperature and their impact on photosynthesis and cell growth.

    • The chemical energy stored in glucose must be released by all cells through a series of enzyme-controlled reactions called respiration.

    • The energy released from the breakdown of glucose is used to generate ATP from ADP and phosphate.

    • The chemical energy stored in ATP can be released by breaking it down to ADP and phosphate.

    • This energy can be used for cellular activities including muscle cell contraction, cell division, protein synthesis and transmission of nerve impulses.

    • ATP can be regenerated during respiration.

    • The breakdown of each glucose molecule via pyruvate to carbon dioxide and water in the presence of oxygen yields 38 molecules of ATP.

    • The breakdown of each glucose molecule via the fermentation pathway yields 2 molecules of ATP when oxygen is not present.

    • Breakdown of glucose to lactic acid via pyruvate in animal cells.

    • Breakdown of glucose to alcohol/ethanol and carbon dioxide via pyruvate in plant and yeast cells.

    • Fermentation occurs in the cytoplasm. Aerobic respiration starts in the cytoplasm and is completed in the mitochondria.

Source: SQA