Download Ms Gentry`s Nucleic acids powerpoint File

Nucleic acids
 Links to G.C.S.E
 D.N.A, genes, chromosomes
 Bonding
Week 17
• State that DNA is a polynucleotide, usually doublestranded, made up of nucleotides containing the bases
adenine, thymine, cytosine and guanine.
• State that RNA is a polynucleotide, usually singlestranded, made up of nucleotides containing the bases
adenine, uracil, cytosine and guanine.
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Key definition
 Nucleotides are the monomers of all
nucleic acids. Each nucleotide is formed
by bonding together
-a phosphate group,
-a sugar molecule (ribose/ deoxyribose)
-an organic nitrogenous base (
Week 17
A single nucleotide
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Sugar group
Week 17
Structure diagrams of phosphate, ribose and deoxyribose sugars
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Week 17
Three nucleotides joined together
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Organic/ nitrogenous bases
There are 5 possible nitrogenous bases, the 4 in DNA
are:
Purine (double)
Pyrimidines (single)
-Adenine
-Thymine
-Guanine
-Cytosine
The 4 in RNA are:
-Adenine
-Guanine
-Uracil (similar to thymine)
-Cytosine
Week 17
Purine and pyrimidine molecules
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Extracting DNA
Uses of DNA extraction
 Genetic testing
 Body identification
 Analysis of forensic evidence
 Study genes involved in disease such as
cancer
Week 17
• State that DNA is a double-stranded polynucleotide.
• Describe how a DNA molecule is formed by hydrogen bonding between
complementary base pairs on two antiparallel DNA strands.
• Explain how twisting of the DNA molecule produces the double helix
shape.
• Outline how DNA replicates semi-conservatively, with reference to the role
of DNA polymerase.
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Key definition
 DNA is a stable polynucleotide molecule. It
acts as an information store because the
bases projecting from the backbone act as
a coded sequence. Organisms differ in
their DNA only because they possess
different sequences of bases in the DNA
Week 17
Part of a DNA part molecule
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Week 17
A-T, C-G and number of hydrogen bonds
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Week 17
A double helix
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Replication
 Takes place during Interphase of the cell cycle
 Chromosomes make copies of themselves
 DNA is unwound and hydrogen bonds between
nitrogenous bases are separated by ‘helicase’ enzymes
(like undoing a zip!)
 Free DNA nucleotides are hydrogen bonded onto the
exposed bases according to base pairing rules by DNA
polymerase enzymes
 Covalent bonds are formed from the phosphate of one
nucleotide and the sugar of the next to seal the backbone.
 This continues along the molecule until 2 new double
helices are formed, each an exact replica of the original
 This is known as semi conservative since each strand
contains one strand from the original and one new strand.
Week 17
DNA replication
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Structure and function
of DNA
 The sequence of bases is an example of
information storage in the form of codes for
proteins.
 Long molecules mean a lot of information can
be stored.
 Base pairing allows for replication.
 The double helix gives great stability.
 Hydrogen bonds allow for unzipping during
copying.
Week 17
• State that a gene is a sequence of DNA nucleotides that
codes for a polypeptide.
• Outline the roles of DNA and RNA in the cells of living
organisms.
• Describe the processes of TRANSCRIPTION and
TRANSLATION
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RNA
RNA is structurally different to DNA
 The sugar molecule that makes up the
nucleotides is RIBOSE
 The nitrogenous base URACIL (U) is found
instead of the organic base THYMINE (T)
 The polynucleotide is usually single
stranded
 3 forms exist
Week 17
RNA types and functions
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Key definition
 A GENE is a length of DNA (part of a
DNA molecule) that codes for one or
more polypeptides. Each gene occupies
a specific place or LOCUS on a
chromosome.
 Different versions of the same gene are
called ALLELES
Making proteins
 The sequence coding for a particular protein is
exposed by splitting hydrogen bonds between the
base pairs
 RNA nucleotides form a complementary strand
called mRNA (messenger) a copy of the original
DNA (TRANSCRIPTION)
 The mRNA peels away and leaves the nucleus
through a nuclear pore and attaches to a ribosome
 tRNA (transfer) brings amino acids to the ribosome
in the correct order according to the base
sequence on the mRNA (TRANSLATION)
 The amino acids are then joined by peptide bonds
to give the primary structure (which then gives rise
to the secondary and tertiary structures)
Week 17
Overview of protein synthesis
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Key definitions
TRANSCRIPTION
 The cells machinery copies the gene sequence
into mRNA (messenger)
TRANSLATION
 The mRNA (gene sequence) is read by a
ribosome and translated into an amino acid
sequence
 The ribosome reads 3 at a time, each group or
CODON corresponds to an amino acid
 Ribosomes know to start at AUG and stop at UAA,
UGA and UAG (stop codons)