NUCLEIC ACIDS & PROTEINS

HL BIOLOGY Van Roekel

11/6/14

BILL

• Draw and label a simplified structure of DNA.

Enzyme Lab

• Lab Report Due – Friday, November 14.• If data is not completed, schedule time with

me to complete it. • Be sure to graph processed data and figure

our averages and standard deviations.• Print copy off, no google docs!

Nucleic Acids• Nucleic Acids are organic compounds that

code for protein sequences.

• REMEMBER: DNA RNAProtein

DNA Structure• Two antiparallel strands in the shape of a

double helix. • Each strand is a chain of nucleotides bonded

together• Nucleotides are composed of phosphate

group, deoxyribose sugar, and one of four nitrogenous bases.

Nucleotide

6

OO=P-O O

Phosphate Group

NNitrogenous base (A, G, C, or T)

CH2

O

C1C4

C3 C2

5

Sugar(deoxyribose)

DNA Structure-Nucleotide

• For HL (IB BIO II) you need to be familiar with the numbering of carbon atom in sugar

DNA Structure- Backbone

• DNA backbone is composed of alternating deoxyribose sugar and phosphate groups

• Held together by covalent bonds called a phosphodiester bond. – Phosphate—oxygen—carbon

DNA Structure-Backbone

• Condensation reactions occur between the phosphate group of the 5’ carbon and the hydroxyl group on the 3’ carbon.

• Nucleotides are always added to the 3’ side of chain.

• DNA strands always have a free 5’ carbon end with a phosphate group and a free 3’ carbon end with a hydroxyl group attached

Nucleotides are bonded together by condensation reactions

11

DNA Structure-Base Pairing

• Nitrogenous bases are held together by hydrogen bonds

• Purines always pair with Pyrimidines• Adenine pairs with Thymine via two hydrogen

bonds• Guanine pairs with Cytosine via three

hydrogen bonds

DNA Structure-Base Pairing

Purines• Double ring structures

Pyrimidines• Single ring structures

2 minute convo• Summarize how nucleic acids are formed.

15

DNA vs RNA

• DNA1- Deoxyribose sugar2- Bases: Adenine, Thymine, Cytosine, Guanine3- Double-stranded helix arrangement

• RNA1- Ribose sugar2- Bases: Adenine, Uracil, Cytosine, Guanine3- Single stranded

17

BILL - Compare DNA and RNA

DNA• Deoxyribose Sugar• Thymine as a base• Double stranded

RNA• Ribose Sugar• Uracil as a base• Single Stranded

DNA Packaging

• DNA is paired with a type of protein called a histone to form a nucleosome

• Nucleosome: the basic unit of DNA packaging– DNA wrapped around two protein molecules, each

of which has 4 different histones– Negatively charged DNA is attracted to Positively

charged histones

DNA packaging-Nucleosome

http://www.youtube.com/watch?v=gbSIBhFwQ4s

DNA Packaging-Nucleosome

• When DNA is wrapped around histones, it is inaccessible to transcription enzymes

• Packaging thus controls transcription process, only allowing certain areas to be involved in protein synthesis

• Nucleosomes are essential to the “supercoiling” of DNA molecules to form chromosomes-tightly packs all genetic material into condensed chromosomes.

DNA Sequencing

• Protein-Coding Sequences– Single copy genes with coding functions. – Provide base sequences essential to produce

proteins at cell ribosomes. – 2% of human genome codes for proteins

• Determined by Human Genome Project: began in 1970s, completed in 2001

DNA Sequencing• Protein-Coding Sequences– Genes are made of numerous fragments of

protein encoding information, and non-encoding fragments.

– Protein encoding fragments are exons– Non-protein encoding fragments are introns

DNA Sequencing

• Highly repetitive sequences– 5-45% of human genome– Composed of 5-300 base pairs per repetition– Up to 100,000 replications….GTTACGTTACGTTACGTTACGTTACGTTAC….– Satellite DNA: clusters of repetitive DNA in

discrete areas• Repetitive DNA does not code for proteins

DNA Sequencing-Structural• Structural DNA is highly coiled DNA that does

not have a coding function. • Generally located around centromere and on

ends of chromosomes. • A.K.A “Pseudogenes” which have no function

Review Questions

• Draw the two strands of a DNA molecule representing their antiparallel relationship and complementary base pairing.

• Explain how nucleosomes would contribute to transcription control.

• Would exons or would introns be more likely to contain highly repetitive sequences? Why?