Nucleic Acids and Protein Synthesis

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DNA: Structure

• Double Helix: Twisted ladder shape of DNA

DNA: Structure

• Monomer: _____________– 5 Carbon Sugar (_________________)– Phosphate– Nitrogenous Base (2 kinds)

Types of Nitrogenous Bases

• Purines:– Adenine (A)– Guanine (G)

• Pyrimidines– Thymine (T)– Cytosine (C)– Uracil (U) – Not in DNA

Nucleotide Structure

DNA Structure

• Double stranded molecule (Ladder)

• Rungs: Nitrogenous bases• Uprights: Alternating Sugar and Phosphates

DNA Structure

• Antiparallel: The 2 strands run in opposite directions

Antiparallel

DNA Structure

• The bases connect the two strands of DNA– Each base ONLY bonds to a corresponding

base• A – T• G – C• NO EXCEPTIONS = Mutations

• Practice: AAGTACTAGATTACCG

Double Helix

• Why does the DNA ladder twist into a double helix?– ANSWER: Hydrophobic vs Hydrophilic

interactions

A DNA Review

• What are the three components of a nucleotide?

• DNA ladder: rungs and uprights

• Antiparallel

• Hydrogen bonding between bases

• Double helix and Hydrophobicity

Famous Scientists

• Chargaff’s Rules (%A = %T, %G = %C)

• Rosalind Franklin (X-Ray Crystallography)– DNA = 2 strands that coil around one another

Famous Scientists Take 2

• Watson and Crick (1953)– 3D molecule of DNA (Double Helix)– Hydrogen bonds between purines and

pyrimidines

DNA and Chromosomes• Prokaryotic Cells (No True nucleus)

– DNA arranged in a large circle

OR- DNA found in small circles (plasmids)

Eukaryotic Cells (True Nucleus)

• DNA is on several linear chromosomes in the nucleus

• Each species has its own unique number of chromosomes– Humans – 46– Fruit fly – 8– Giant Sequoia Tree – 22

DNA is huge . . . How can it fit in the nucleus?

• DNA winds around protein complex (Histones)

How it fits continued…

• DNA and Histone complex coil to form a Nucleosome

• Nucleosomes coil tighter (Supercoil) to form a chromomome

Histones and Evolution

• Histones are very conserved throughout among different species– Conserved – similar structure and amino acid

sequence due to evolution

• WHY???

DNA Replication

• When does it occur?

• Why does it occur?

• How does it occur (5 steps)?– Uncoil– Unzip– Add parts– Recoil– Proof-read

DNA Replication Take 2

• The process is controlled by many enzymes• Steps in detail:

1. Uncoil

2. Unzip– DNA helicase unzips the 2 DNA molecules by

breaking the Hydrogen bonds between the bases– Typically begins at a site rich in A’s and T’s. WHY?

DNA Bases

Result: Replication Fork

DNA Replication3. Add parts

– Each strand serves as a template for the construction of a seconds strand of DNA

– Problem: The 2 strands are anti-parallel– Solution:

• One strand copied continually – Leading strand• One strand copied in segments – Lagging strand

DNA Replication

• Leading strand = 3’ 5’• Lagging strand = 3’ 5’ but leaves gaps

– Gaps = Okasaki Fragments

DNA Replication

3. Add Parts– DNA Polymerase begins adding

corresponding nucleotides to the template strands

EX) ATTATACG

TAATATGC– When finished, DNA Polymerase comes

back and fills in the gaps (Okasaki fragments)

DNA Replication

4. DNA Recoiled

5. DNA is proof-read– DNA Polymerase proof-reads the 2 strands of

DNA for any mistakes

Result: 2 strands of DNA

Semi-conservative: Definition?

Sex Determination and Sex Linkage

• Sex is determined by the 23rd chromosomes

XX =

XY =

Chances of Having Male vs Female Child

• Hypothetical Sex ratio:

• Birth Ratio:

• Population Ratio:

• Kutztown Ratio:

X-Linked Traits

• The x chromosome is bigger than the y and therefore holds more genes

Examples:

- Hemophilia

- Red/Green Color-blindness

- Baldness

Sex Linked crosses

• These are all recessive traits (For our purposes)• Females must have two bad copies in order to

be infected– XX– XXC

– XCXC

• Males only need one bad copy– XY– XCY

Morale of this story

• Who is responsible for a son being bald?Cross One: Cross a bald man with a

homozygous normal woman

Cross Two: Cross a normal man with a woman carrying the bald gene.

RNA and Protein Synthesis

• RNA (Ribonucleic Acid

• Type of Nucleic Acid (3 parts)

RNA VS DNA

• RNA is single stranded

• RNA’s sugar is Ribose, not Deoxyribose

• RNA uses Uracil (U) as a base rather than Thymine (T)– Uracil connects to Adenine (A)

Types of RNA

• Messenger RNA (mRNA)

• Ribosomal RNA (rRNA)

• Transfer RNA (tRNA)

What is the job of RNA

Ribosome