nucleic acids unit: nucleic acids nucleus dna structure dna replication
TRANSCRIPT
Nucleic Acids Unit: Nucleic Acids
NucleusDNA structure
DNA replication
All living things…
• What are the characteristics of all living things?
Deoxyribonucleic Acid (DNA)
One of several nucleic acidsContained in the cell nucleus (eukaryotes)Hereditary information (passed on parent to child)Copied before cell divisionCodes for proteins – the building blocks for all cell materials,
activities, and traits
Nucleic Acids
• Nucleic acids are long chains of nucleotides• Nucleotides are molecules with a five-carbon sugar, a phosphate
functional group, and a nitrogen-containing base• Nucleotides are building blocks
Nucleotides: Two main groups
Deoxyribose Nucleotides
• Deoxyribonucleic acid (DNA): chromosomes
Ribose Nucleotides
• Ribonucleic acid (RNA): protein synthesis
• Adenosine triphosphate (ATP): energy
Deoxyribonucleic Acid (DNA): Structure• Four nucleotides (deoxyribose sugar, phosphate group, nitrogenous
base) arranged in a double helix pattern (twisted ladder)• Purines• Adenine (A)• Guanine (G)
• Pyrimidines• Cytosine (C)• Thymine (T)
Deoxyribonucleic Acid (DNA): Structure• Bases pair up like rungs in the
center with a weak hydrogen bond (attraction between a positive and negative charge)• A sugar/phosphate backbone
forms each side of the ladder • What do you notice about the
base pairing? • A-T, C-G are the complementary
base pairs
Deoxyribonucleic Acid (DNA): ProkaryotesProkaryote• Single, circular DNA molecule
called the chromosome and has all the information for functioning• Plasmid is a separate, very small
circle of DNA used for special information like antibiotic resistance
• Reproduction? • Asexual by binary fission (divide
in two, similar to mitosis)• Pili? Conjugation allows bacteria
to exchange information like plasmids
Deoxyribonucleic Acid (DNA): EukaryotesEukaryote• Much more DNA enclosed in
nucleus• Varying number of
chromosomes• Humans: 23 pairs of
chromosomes (46 total)• Approximately 3 billion base
pairs
DNA: Variation and Specialization • All living organisms have DNA based on the same four base pairs• Sequence of base pairs determines proteins produced (all traits!) • Specialization of cells determines which part of the DNA is active in
each unique cell (every cell in an organism has the same DNA)
Try this!
DNA: In the cell
DNA: Nucleus
• Three major parts:• Nuclear envelope• Chromatin• Nucleolus
DNA: Nucleus
• Nuclear envelope (membrane) – Selectively permeable double membrane (allows small molecules through but large molecules go through a protein gate)
• Chromatin – DNA and associated proteins that forms long strands called chromosomes; condenses for cell division
• Nucleolus – site of ribosome synthesis
DNA: Cell DivisionMitosis Stage Activity Definitions
Interphase DNA is in relaxed form called chromatin. During S phase it is replicated.
Chromatin: DNA of eukaryotic cells
Prophase DNA already copied. It begins to condense to form chromosomes (paired chromatids). Spindle fibers attach to kinetochore of each sister chromatid
Sister chromatid: One of two identical strands of DNA that forms a duplicated chromosome, joined at centromere
Metaphase Sister chromatids line up in the middle
Anaphase Sister chromatids are pulled apart becoming independent daughter chromosomes
Chromosomes: DNA double helix together with proteins.
Telophase Chromosomes return to relaxed chromatin form
DNA: Helix to Chromosome
Watch Here
DNA: Replication
• During S phase of interphase DNA is copied so there will be one identical set for each new daughter cell • Replication of DNA depends on the complementary base pairs
1. Unwind the DNA2. Match complementary base pairs to each side3. Two new identical DNA strands produced
DNA: Replication
1. Unwind the DNA
DNA helicases – enzymes pull the DNA apart by breaking hydrogen bonds between the base pairs
DNA: Replication
2. Match complementary base pairs to each side
DNA polymerases – enzymes move along each parent DNA strand and match complementary nucleotides
DNA: Replication
3. Two new identical DNA strands producedSemi-conservative process – Each daughter DNA strand has half parental DNA and half new DNA and winds back together to form the double helix
DNA: Replication
Mistakes? Very rare but can happen Mistakes are called mutations and can be fatal, indifferent, or good depending on what they do to protein synthesis Point mutation (one base pair wrong) Insertion mutation (extra base) Deletion mutation (lose base) Inversion (piece of DNA cut out and moved into a gap) Translocation (piece of DNA removed and attached to another
chromosome)