DNADeoxyribose Nucleic Acid

DNA• DNA is a double helix.

• A bonds to T: C bonds to G

• In man, the DNA molecule , if fully extended, would have a total length of 1.7 metres. If you unwrap all the DNA you have in all your cells, you could reach the moon ...6000 times!

DNA

•DNA STRUCTURE•DNA REPLICATION

Components of DNA• NUCLEOTIDE

– Phosphate group-phosphodiester bond– 5-Carbon sugar-deoxyribose– nucleic acid (1 of the nucleic acids)

• Guanine-Purine• Cytosine-Pyrimidines • Adenine-Purine• Thymine-Pyrimidines • Held by hydrogen bonds• One end of chain with free 5’ phosphate group

• Other end of chain with free 3’ hydroxyl group

• Adenine, thymine form two bonds• Guanine, cytosine form three bonds

COMPONENTS

DNA Replication• DNA is opened by enzymes (unzips) helicase

• Complementary nucleotides bond with the old strands-

• 2 strands created: ½ is the old strand; ½ is the new strand.

DNA REPLICATION• TAKES PLACE IN THE NUCLEUS

• END PRODUCT IS TWO IDENTICAL STRANDS

• DURING CELL DIVISION- ONE STRAND

• FOR EACH CELL

• Replication occurs only in 5’(P) to 3’(OH) direction(DNA IS READ 3’ to 5’)

• a. Replication of leading strand, 3' to 5' strand

• 1. New strand grows from 5' to 3’end• 2. Elongates towards replication fork

REPLICATION

ENZYMESHelicaseDNA polymeraseTopoisomeraseRNA primerligase

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From Genotype to PhenotypeFrom Genotype to Phenotype

• Protein synthesis--converting the genetic code (in DNA) into proteins that the body uses

• 3 Steps involved– Transcription– RNA splicing– Translation

• Protein synthesis--converting the genetic code (in DNA) into proteins that the body uses

• 3 Steps involved– Transcription– RNA splicing– Translation

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DNA----RNA

• DNA• DOUBLE

STRANDED• DEOXYRIBOSE• NUCLEIC BASES

– THYMINE

– GUANINE

– ADENINE

– CYTOSINE

• RNA• SINGLE STRANDED• RIBOSE• NUCLEIC BASES

– URACIL

– GUANINE

– ADENINE

– CYTOSINE

RNA Differences from DNA

– Single stranded (vs. Double stranded DNA)– Contains uracil in place of thymine– Ribose sugar (instead of deoxyribose)

4 Types of RNA preMRNA---transcribes the message from the

DNA(rough blueprint)– mRNA (messenger RNA)-carries message to to

ribosome(final blueprint) – rRNA (ribosomal RNA)--makes up the

ribosome(forman that assembles parts of protein in a specific order)

– tRNA(transfer RNA)--carries amino acids to ribosomes

tRNA• Anticodon of MRNA• Wobble to take in all

possible aa combinations of 3 nitrogen bases

• Carries specific aa on 3’ on of strand

DNA TRANSCRIPTIONDNA- GIVES CODE TO preRNA

or hnRNA

PROCESSING

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RIBOSOME STRUCTURE

A site - attracts Trna

P site - forms peptide bonds between aa of protein

E site - where Trns leave ribosome and aa chain elongates

5’ end with initiator sequence attaches to small subunit

Large subunit goes over small at the A site.

Attracts 1st Trna with aa Met

DNA TRANSLATIONtRNA translates mRNA into proteins

SUMMARY

Comparison of DNA and RNA• RNA is single stranded

• RNA has uracil instead of thymine

• A-U

• DNA is double stranded

• DNA has thymine instead of uracil

• A-T

Understanding DNA

• Inheritance/ Genetic Counseling• Cell function/protein synthesis• Embryonic development/gene regulation

• Evolution/ phylogenetic relationships

• Medicine/genetic diseases• Genetic engineering/ recombinant DNA

Changes in Chromosomes

• Mutation--a change in the sequence of DNA nucleotides (nitrogen bases)– Causes a change in the protein formed– Causes a change in organisms’ phenotype (trait)

• Effects of mutations?– Some have little or no effect– A few are beneficial– Most are harmful or lethal (fatal)

Chromosomal Mutations• Deletion mutation--piece of chromosome breaks off and is lost; the new DNA strands are also missing a piece

• Duplication--piece of chromosome breaks off and is inserted on homologous chromosome

• Translocation--piece of chromosome breaks off and attaches to a different, non-homologous chromosome

• Inversion--piece of chromosome breaks off, turns around and reattaches in opposite direction

Mutations Illustrated

Gene mutations

• Frameshift mutation--deletion or addition of single (or few) nucleotides alters the amino acid sequence of the protein

• Point (Substitution) mutation--wrong base is added in a position--new DNA chains will show the change

Point Mutations

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MUTATIONS

Frameshift Mutations

Expansions are responsible for many genetic diseases:

• Muscular Dystrophy (CTG repeats)

• Huntington’s (CAG repeats)

• Fragile X (CCG repeats)

Replication Errors and Mutations

• Inheritance of mutations– Harmful mutations

•Individuals may not live to reproductive age

•Individuals may not develop/adapt as well

– Advantageous mutations•Help survival of organism and are passed down if mutation occurred in cells that produce gametes

Genes and cancer

• Cancer is uncontrolled, abnormal cell division– Apoptosis--programmed cell death, which

is necessary for normal functioning

• Cause of cancer?– Genes that control production of new cells

don’t turn off

Genetic causes of cancer

• Oncogenes--cause cell to become cancerous

• Genes become oncogenes in 3 ways– Mutation can occur in a growth-factor gene,

causing rapid, uncontrolled cell growth– Error in DNA replication, producing multiple

copies of a single-growth factor gene– Change in gene’s location--falls under the

control of a different promoter is transcribed more often (producing more growth-factor)

Tumor suppression

• Humans have tumor-suppressor genes which are natural “anti-oncogenes”– If tumor suppressor gene is mutated, uncontrolled

growth/reproduction occurs

• Retinoblastoma--inheritable cancer in eyes caused by changes in tumor-suppressor gene on chromosome 13– Can also occur when mutations occur in an individual (not

always inherited)

• Identifying location of these genes can increase identification and treatment of cancer