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

• http://www.classzone.com/cz/books/bio_09/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:

https://www.pearsonsuccessnet.com/snpapp/learn/navigateIDP.do?

method=toc&newServiceId%20=10363&product_isbn=0-

13-361474-3

http://www.youtube.com/watch?v=zdDkiRw1PdU

Practice replication at www.biology.com

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__ N A I S _ _ E U N I V E R S A L

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C O D E O F L I F E

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

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

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

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

http://www.youtube.com/watch?v=_6Rrymt6XwI

Practice at www.classzone.com

• http://www.classzone.com/cz/books/bio_09/get_chapter_group.htm?cin=3&ci=8&rg=animated_biology&at=animated_biology&npos=2&spos=8&var=animated_biology

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.

• https://www.pearsonsuccessnet.com/snpapp/learn/navigateIDP.do?method=toc&newServiceId%20=10363&product_isbn=0-13-361474-3

Practice at www.biology.com