Nucleic Acids Unit: Nucleic Acids Nucleus DNA structure DNA replication

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)