Fundamentals of Biological Sciences
Lecture2
Dr. Açelya Yılmazer
NUCLEUS – THE INFORMATION STORE
• Nucleus (nuclei pl.): the most prominent organelle in an eukaryotic cell.
• Enclosed within 2 concentric membranes (nuclear envelope)
• Contains DNA molecules (carrying genetic information)
• In prokaryotes, DNA is again the genetic
material but not enclosed in an envelope
THE STRUCTURE OF DNA
• Life depends on the stable storage and inheritance of genetic information.
• Genetic info is carried by DNA molecules (deoxyribonucleic acid)
• The genetic info is encoded in the linear seqeunce of 4 nucleotides (A, T, G, C)
• A DNA Molecule Consists of Two Complementary Chains of Nucleotides
– Double helix – Antiparallel
– Complimentary
– Hydrogen bonding required for AT and GC pairing
• The Structure of DNA Provides a Mechanism for
Heredity
WATCH VIDEO – DNA
STRUCTURE
THE STRUCTURE OF DNA
• Life depends on the stable storage and inheritance of genetic information.
• Genetic info is carried by DNA molecules (deoxyribonucleic acid)
• The genetic info is encoded in the linear seqeunce of 4 nucleotides (A, T, G, C)
• A DNA Molecule Consists of Two Complementary Chains of Nucleotides
– Double helix – Antiparallel
– Complimentary
– Hydrogen bonding required for AT and GC pairing
• The Structure of DNA Provides a Mechanism for
Heredity
THE STRUCTURE OF EUKARYOTIC CHROMOSOMES
• Eukaryotic DNA Is Packaged into Multiple Chromosomes
• Chromosomes Contain Long Strings of Genes
• When a gene is expressed, part of its nucleotide seqeunce is transcribed into RNA molecules, many of which are translated into proteins.
• The total genetic info carried by all the
chromosomes in a cell or organism: genome
• Specialized DNA Sequences Are Required for DNA
Replication and Chromosome Segregation
THE STRUCTURE OF EUKARYOTIC CHROMOSOMES
• The DNA in Chromosomes Is Always Highly Condensed
• In eukaryotes, DNA is tightly folded by binding to a set of proteins.
• Chromatin: nuclear DNA complexed with proteins
• Two types of proteins in DNA: histones and non- histone proteins
• Nucleosomes Are the Basic Units of Eukaryotic Chromosome Structure
– They are the first and fundamental level of chromatin packing
• Chromosome Packing Occurs on Multiple Levels
THE STRUCTURE OF EUKARYOTIC CHROMOSOMES
• The DNA in Chromosomes Is Always Highly Condensed
• In eukaryotes, DNA is tightly folded by binding to a set of proteins.
• Chromatin: nuclear DNA complexed with proteins
• Two types of proteins in DNA: histones and non- histone proteins
• Nucleosomes Are the Basic Units of Eukaryotic Chromosome Structure
– They are the first and fundamental level of chromatin packing
• Chromosome Packing Occurs on Multiple Levels
THE REGULATION OF CHROMOSOME STRUCTURE
• Changes in Nucleosome Structure Allow Access to DNA
• Therefore a cell can regulate its chromatin structure
(condense/decondense particular regions). – chromatin remodeling complexes
• Loosining of chromatin: gene expression, DNA replication, DNA repair mechanisms
• Interphase Chromosomes Contain Both Condensed and
More Extended Forms of Chromatin
THE REGULATION OF CHROMOSOME STRUCTURE
