Higher Biology SQA

This subject is broken down into 70 topics in 6 modules:

  1. DNA and the Genome 8 topics
  2. Metabolism and Survival 7 topics
  3. Sustainability and Interdependence 8 topics
  4. Cells and Proteins 18 topics
  5. Organisms and Evolution 19 topics
  6. Investigative Biology 10 topics
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This page was last modified on 28 September 2024.

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Biology

DNA and the Genome

The Structure of DNA

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The Structure of DNA

Structure of DNA

DNA Components

  • DNA (Deoxyribonucleic Acid) is a type of genetic material found in living organisms. It controls physical characteristics and cellular functions.

  • The DNA molecule consists of two polynucleotide chains twisted around each other to form a double helix.

  • Each polynucleotide chain is made up of nucleotide subunits.

  • Nucleotides consist of a phosphate group, a deoxyribose sugar and a nitrogenous base.

  • Four different nitrogenous bases exist in DNA: adenine (A), thymine (T), guanine (G), and cytosine (C).

Base Pairing and Bonding

  • In DNA, bases pair in a specific manner: adenine pairs with thymine (A-T), and guanine pairs with cytosine (G-C). This is also known as complementary base pairing.

  • Each base pair is held together by hydrogen bonds: Two between A-T and three between G-C.

  • The phosphate group of one nucleotide binds to the deoxyribose sugar of the next nucleotide, forming a sugar-phosphate backbone. This is a result of a covalent bond, which are strong and stable.

Double Helix Structure

  • The two polynucleotide chains run anti-parallel to each other, meaning they run in opposite directions.

  • This double helix structure is twisted, creating major grooves and minor grooves.

Genome and Chromosomes

  • The genetic information carried by an organism is its genome.

  • This genome is divided into chromosomes, which are further divided into genes.

  • Each gene has the instructions necessary for the production of a particular protein.

  • Different species have different number of chromosomes. Humans have 46 (23 pairs).

  • Each chromosome is a long, linear DNA molecule associated with proteins called histones. The DNA-histone complex is known as chromatin.

Remember, understanding the structure of DNA is fundamental to biology as it helps explain how genetic information is stored, transferred, and manifested as physical traits.

Course material for Biology, module DNA and the Genome, topic The Structure of DNA

Biology

Cells and Proteins

Hydrophobic Signals and Control of Transcription

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Hydrophobic Signals and Control of Transcription

Hydrophobic Signals:

  • Hydrophobic signals are substances like hormones that cannot dissolve in water.
  • These hydrophobic chemicals are often small, allowing them to easily pass through the cell membrane.
  • Examples of hydrophobic signals include steroids and thyroid hormones.
  • Upon entering the cell, they bind to certain types of proteins called intracellular receptors.

Impact on Proteins:

  • Hydrophobic signals can alter the shape of these receptor proteins, changing their function. This is known as an allosteric change.
  • Most intracellular receptors are found in the cytosol, but some are located in other parts of the cell, like the nucleus.
  • When a hydrophobic signal binds to the receptor, the resulting complex often acts as a transcription factor, influencing the transcription of specific genes.

Control of Transcription:

  • Transcription is the process where regions of DNA are copied to mRNA (messenger RNA), a vital step in gene expression and protein synthesis.
  • Transcription factors like receptor-signal complexes can either promote or inhibit transcription. This is crucial for the regulation of gene expression.
  • In the nucleus, the transcription factor complex binds to specific regions of DNA, causing the initiation of transcription.
  • The control of transcription by hydrophobic signals allows cells to respond in a specific and coordinated way to these signals, affecting many aspects of cell behaviour and physiology.

Understanding hydrophobic signals and control of transcription will provide a deeper understanding of cell communication and gene expression mechanisms. Ensure you understand how the signalling and transcription process works, as these are key to many biological processes.

Course material for Biology, module Cells and Proteins, topic Hydrophobic Signals and Control of Transcription

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