DNA Processes: Replication, Transcription, & Translation.
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Transcript of DNA Processes: Replication, Transcription, & Translation.
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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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