A comprehensive, detailed study guide of all the DNA content required for the IEB Life Science paper 1. This includes the history of DNA, DNA and RNA, mtDNA, DNA replication, transcription and translation in protein synthesis, Meiosis and Mitosis, Genetic variation, Inheritance, gene mutations, chr...
DNA NOTES LUCY VAN DER MEULEN
Definitions:
Nucleus - a dense organelle present in most eukaryotic cells, typically a single rounded structure bounded by a double
membrane, containing the genetic material.
Chromosome - a threadlike structure of nucleic acids and protein found in the nucleus of most living cells, carrying genetic
information in the form of genes.
Chromatin network - a mass of genetic material composed of DNA and proteins that condense to form chromosomes during
eukaryotic cell division.
Nucleic Acid - a complex organic substance present in living cells, especially DNA or RNA, whose molecules consist of many
nucleotides linked in a long chain.
DNA - deoxyribonucleic acid, a self-replicating material which is present in nearly all living organisms as the main constituent
of chromosomes. It is the carrier of genetic information.
Nucleosome - a structural unit of a eukaryotic chromosome, consisting of a length of DNA coiled around a core of histones.
Gene - a unit of hereditary which is transferred from parent to o spring and is a distinct sequence of nucleotides forming
part of a chromosome, the order of which determines protein synthesis
Genome - the haploid set of chromosomes in a gamete or microorganism, or in each cell of a multicellular organism.
Histone - any of a group of basic proteins found in chromatin.
Polymer - a substance which has a molecular structure built up chiefly or completely from a large number of similar units
bonded together
Monomer - a molecule that can be bonded to other identical molecules to form a polymer
Nucleotide - a compound consisting of a nucleoside linked to a phosphate group. Nucleotides form the basic structural unit
of nucleic acids such as DNA.
Semi-conservative model - relating to or being genetic replication in which a double-stranded molecule of nucleic acid
separates into two single strands each of which serves as a template for the formation of a complementary strand that
together with the template forms a complete molecule.
DNA replication - DNA replication is the process by which a double-stranded DNA molecule is copied to produce two
identical DNA molecules.
Interphase - the resting phase between successive mitotic divisions of a cell, or between the first and second divisions of
meiosis.
Centromere - the region of a chromosome to which the microtubules of the spindle attach during cell division.
Chromatid - each of the two threadlike strands into which a chromosome divides longitudinally during cell division. Each
contains a double helix of DNA.
RNA - ribonucleic acid, a nucleic acid present in all living cells. Its principal role is to act as a messenger carrying
instructions from DNA for controlling the synthesis of proteins
Allele - each of two or more alternative forms of a gene that arise by mutation and are found at the same place on a
chromosome.
1
,The Nucleus
A dense organelle present in most eukaryotic cells, typically a single rounded structure bounded by a double
membrane, containing the genetic material
Parts of the nucleus:
● The nucleus is surrounded by a double nuclear
membrane with pores
● The nuclear pores form a passage between the
nucleus and cytoplasm of the cell
● The nucleoplasm is a jelly-like liquid
● The nucleolus is a small, round body which is
suspended in the nucleoplasm
● The chromatin network is a mass of thread-like
structures
● When the cell divides, the chromatin network coils and thickens into seperate, shorter thread-like
structures called chromosomes.
● Chromosomes are the carriers of genetic material in a cell
Functions of the nucleus:
● The chromosomes in the nucleus store the genetic material of the cell
● The nucleus regulates the structure and metabolism of the cell
Nucleic Acid
A complex organic substance present in living cells, especially DNA or RNA, whose molecules consist of many
nucleotides linked in a long chain
● Nucleic acids are organic molecules that control the synthesis of proteins in all living cells by
storing and transferring genetic material
● Types of nucleic acids in living cells:
- DNA (deoxyribonucleic acid)
- RNA (ribonucleic acid)
DNA - Deoxyribonucleic acid
A self-replicating material which is present in nearly all living
organisms as the main constituent of chromosomes. It is the
carrier of genetic information
Location:
● Chromosomal DNA occurs in the nucleus where it
forms part of the chromatin network/chromosomes
● Extranuclear DNA occurs outside the nucleus in the
mitochondria and chloroplasts (plants only)
2
,Chromosomes and genes
Chromosome - a threadlike structure of nucleic acids and protein found in the nucleus of most living cells,
carrying genetic information in the form of genes
(Long, thin, thread-like structures composed of DNA that is wrapped around proteins called histones)
Only visible in a dividing cell
Histones - any of a group of basic proteins found in chromatin
Gene - a unit of heredity which is transferred from a parent to o spring and is held to determine some
characteristic of the o spring
(A short segment of a DNA molecule that codes for a particular protein and controls and inherited characteristics
and determines the appearance and functioning of an organism)
Discovery of the structure of DNA
3
, Summary of the discovery of DNA:
In the early 1950’s James Watson and Francis Crick were both doing postgraduate research at the University of
Cambridge in England and became involved in DNA research. At this stage, research showed that the genetic
material was DNA, but the structure of the molecule was still unknown. Erwin Charga discovered that there were
equal numbers of base pairs Adenine - Thymine and Guanine - Cytosine in a DNA molecule. Maurice Wilkins and
Rosalind Franklin were also doing research on the DNA structure at King’s College in London. In 1952 they took an
X-ray photograph of the DNA molecule and Franklin surmised that DNA was helix-shaped. Wilkins showed Franklin’s
X-ray photograph to Crick without her permission and Watson and Crick used the information to build three
dimensional models of the DNA structure.
Structure of DNA
● DNA is a giant molecule which consists of two strands that are twisted to form a double helix
● DNA is a polymer made up of large numbers of similar units called monomers (building blocks)
● Nucleotides are the monomers of DNA
(poly = many and mono = one)
Nucleotides
a compound consisting of a sugar molecule, nitrogenous base and a
phosphate group. Nucleotides form the basic structural unit of nucleic
acids such as DNA
Four di erent types:
- Adenine (A)
- Guanine (G)
- Cytosine (C)
- Thymine (T)
Adenine and Guanine - large molecules known as purine bases (Pure as gold)
Cytosine and thymine - smaller molecules known as pyrimidine (CU(RNA)T the py)
Formation of a nucleotide
1. Deoxyribose combines with the phosphate group
2. One nitrogenous base combines with deoxyribose
As there are four di erent nitrogenous bases, there are four di erent nucleotides in a DNA molecule
Formation of DNA
1. The deoxyribose of one nucleotide forms a bond with the phosphate group of another
2. Two long strands, resembling the sides of a ladder are formed
(The sides of the ladder consists of alternating deoxyribose molecules and phosphate groups)
3. Each step of the DNA ladder is formed by the linking of two nitrogenous bases - a large purine and a small
pyrimidine and are called a base pair
4
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