This document is designed to help students with DNA topic as DNA is a very tricky topic and there is mostly always a question in the exam paper of them so it is better to learn the key points. And it has exam-style questions too.
Liver and muscle cells have large numbers of mitochondria due to large amounts
of respiration taking place. Some structures in cells, such as ribosomes, are too
small to be seen with the light microscope. Ribosomes are in the cytoplasm and
are the site of protein synthesis.
DNA Structure and Genetic Code:
Describe the structure of DNA as two strands coiled to form a double helix, each
strand containing chemicals called bases, of which there are four different types,
with cross links between the strands formed by pairs of bases.
- A chromosome is a long, coiled molecule of DNA, divided up into regions
called genes.
- Each gene contains a different sequence of bases and codes for a
particular protein.
- Proteins are made in the cytoplasm; a copy is made from the nucleus
because the gene itself cannot leave the nucleus.
- The four bases of DNA are A, T, C and G. Complementary base pairings: A
– T and G – C.
The base pairs
- Protein structure is determined by the DNA base code, to include: the base
sequence determines amino acid sequence and each amino acid is coded
for by a sequence of 3 bases
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, Molecules for Life – Revision Pack
Ribosomes are the site of protein synthesis. They are found in the cytoplasm but
DNA is found in the nucleus. The genetic code needed to make a particular
protein is carried from the DNA to the ribosomes by a molecule called mRNA.
Making:
- mRNA from DNA is called transcription
- Proteins from mRNA is called translation
Ribosomes are smaller than mitochondria and are found in the cytoplasm. They
are too small to be seen with a light microscope.
The code needed to produce a protein is carried from the DNA to the ribosomes
by a molecule called mRNA.
DNA controls cell function by controlling the production of proteins, some of
which are enzymes.
Discovery of DNA Structure:
Watson and Crick used data from other scientists to build a model of DNA, using
X-ray data showing that there were two chains wound in a helix and data
indicating that the bases occurred in pairs.
New discoveries, such as Watson and Crick’s, are not accepted or rewarded
immediately. Here are reasons why:
- Other scientists repeating or testing the work gives public confidence if
their studies back up the original studies
- Other theories were more widely accepted
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