DNA Processes: Replication, Transcription, & Translation

DNA Replication Replication – the process of making a copy of DNA Takes place in the nucleus of cells Takes place during the S-phase of the cell cycle More than a dozen enzymes involved –Enzymes can be identified b/c they usually end is –ase Ex. Phosphofructokinase

Enzymes review What type or organic compound are enzymes? Which are the monomers that make up enzymes? What is a polypeptide? What is the function of an enzyme? How do enzymes affect activation energy? List three factors that affect how enzymes work. How are structure and function related? Use the terms enzyme, substrate, active site, reactant, product.

Replication Process Step 1: –Helicase splits the two DNA strands beginning with an A=T bond, breaking weak H bonds. (Think of unzipping a sweatshirt.)

Replication Process cont. Step 2: –DNA polymerase binds complementary free- floating nucleotides to each strand. (Each original strand, now unzipped, serves as a template for complementary nucleotides to attach.)

Step 2

Replication Process cont. Step 3: –DNA polymerase proofreads, or checks to make sure there are no errors and that each new DNA is identical

Replication End Product Semi-conservative replication Each of the 2 new DNA molecules have one new strand and one old strand from the original (parent) DNA molecule.

Replication Animation 9/get_chapter_group.htm?cin=3&ci=8&rg= animated_biology&at=animated_biology& npos=2&spos=8&var=animated_biologyhttp:// 9/get_chapter_group.htm?cin=3&ci=8&rg= animated_biology&at=animated_biology& npos=2&spos=8&var=animated_biology

Practice creating a complementary strand:

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DNA Codes For Traits Genes – units of inherited information found in DNA. –Code for inherited traits –The codes are written in the sequence of bases. Different sequence of bases = different trait ~Different letters = different words (ant vs tan) DNA  RNA  PROTEINS

RNA –Ribonucleic acid Has ribose as sugar instead of deoxyribose –Always single stranded –Uracil (U) instead of Thymine (T) C=G A=U

DNA  RNA  PROTEINS –Three types of RNA mRNA – messenger RNA (carries copies of instructions from DNA) tRNA – transfer RNA (carries amino acids during protein synthesis) rRNA – ribosomal RNA (combines with proteins to form ribosomes)

DNA  RNA  PROTEINS Proteins –Do the work in our bodies (chemical reactions) –Contribute to our characteristics

DNA  RNA Transcription – the process of making mRNA from DNA –A.K.A. RNA synthesis (build) Takes place in the nucleus of cells Allows coded instructions from DNA to get out of the nucleus

Transcription (RNA synthesis)

DNA  RNA (transcription) Step 1: –RNA polymerase unwinds and unzips the DNA double helix and scans DNA to find a starting point. Step 2: –One strand of DNA is used as a pattern or template as RNA polymerase joins complementary RNA nucleotides (1000’s of mRNA copies can be made) Step 3: –mRNA is released into the cytoplasm of the cell. (How does it get out of the nucleus?) –DNA “zips” back together

Transcription TRANSCRIPTION ANIMATION

Transcription Animation yJGZQ

DNA = TAC - CCG - TAA - CTA - GCT - TTA RNA =

DNA = TAC - CCG - TAA - CTA - GCT - TTA RNA = AUG - GGC - AUU - GAU - CGA - AAU

Codons Every 3 bases of mRNA codes for a specific amino acid –Amino acids (building blocks or subunits of proteins) are bonded together to make proteins (polypeptides)

RNA= UCG 

RNA= UCG  Serine

RNA= AUG  Methionine - START

RNA= UGA 

RNA= UGA  STOP

DNA = TAC - CCG - TAA - CTA - GCT - TTA RNA = AUG - GGC - AUU - GAU - CGA - AAU A.A. = MET - GLY - ISO - ASP - ARG - ASG

RNA  PROTEINS Translation -making proteins from the nucleic acid code found in mRNA— like translating a code. tRNA – transfer RNA – translates the 3 letter codons into proteins –tRNA has an anti-codon – a 3 letter sequence complementary to the mRNA codons that corresponds to a certain amino acid

Translation Takes place at the ribosomes of the cell –Each ribosome is made of 2 subunits –Each subunit is made of proteins and ribosomal RNA (rRNA) –Ribosomes are the tiny organelles known as protein factories

Translation Process Step 1: –the ribosome and strand of mRNA attach in the cytoplasm (NOT in the nucleus) Step 2: – tRNA arrives with the correct amino acid. Amino acids bond together. As new tRNA molecules arrive older ones depart. Amino acids continue to bond together forming growing polypeptide chains (peptide bonds stick the amino acids together)

Translation Process Step 3: –Termination “END” codon is reached All parts are disassembled

After translation… Protein is released Can travel through ER Be modified, packaged, sorted in the Golgi Apparatus Contained in a vesicle for transport within or out of the cell Active and passive transport…

DNA TRANSLATION ANIMATION 6Rrymt6XwI

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33 Processes Replication: DNA copied into DNA Transcription: DNA copied into mRNA Translation: message turned into protein

Genetic Mutations Mutation – any change in the nucleotide sequence of DNA. –Can involve an entire chromosome –Can involve large regions of DNA –Can involve a single base 2 Categories of Gene Mutations –Substitutions –Deletions / Insertions (Frameshift)

Substitutions can be harmless as long as they are not in a region that codes for a gene

–A frameshift mutation inserts or deletes a nucleotide in the DNA sequence. All subsequent amino acids may be affected (typically more severe than substitution).

Deletions / Insertions throw the entire sequence off. VERY VERY BAD!!!

What causes mutations? Errors during DNA replication Errors during crossing over (Meiosis I) Mutagens –Physical or chemical agents that cause DNA mutations –Examples: High-energy radiation  X-rays & UV light Virus Drugs ***THINK--ARE ALL MUTATIONS BAD?

Sex cells vs Body cells Mutations in sex cells (sperm or egg) are inheritable Mutations in body cells are not passed on

Mutations practice 1. Write a DNA code 24 letters long. Label it DNA template. Transcribe it into mRNA. Translate it into a protein. 2. Copy the original DNA showing an example of ONE point mutation (substitution). Label it DNA with point mutation. Transcribe it into mRNA. Translate it into a protein.

3. Follow the same instructions as in step 2, except create a frameshift mutation instead of a substitution. Are there any differences in the protein? How many? Which type of mutation had a more severe effect?

Gene Expression All of our cells have the exact same copy of DNA Cells look and function differently (skin and white blood cell)—why? Different genes are turned on and off, like light switches, at different times during our development (causing cell differentiation) Environmental factors can influence gene regulation and expression –Ex. Temperature can affect moth development

Phenotype Expression of gene –Examples: height, color, blood type *Controlled by genes; can be affected by environment. You may have a gene that makes you more likely to get skin cancer, but if you rarely go out in the sun, you will decrease your chance of getting cancer. The UV rays from the sun may be more likely to turn “on” your switch for skin cancer.

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