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BIOL 1543, Chapter 25

by: Kenzie Miller

BIOL 1543, Chapter 25 BIOL 1543

Marketplace > University of Arkansas > Biology > BIOL 1543 > BIOL 1543 Chapter 25
Kenzie Miller
GPA 4.0

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These notes cover the main topics of chapter 25.
Principles of Biology
Dr. Shadwick
Class Notes
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This 16 page Class Notes was uploaded by Kenzie Miller on Friday October 14, 2016. The Class Notes belongs to BIOL 1543 at University of Arkansas taught by Dr. Shadwick in Fall 2016. Since its upload, it has received 82 views. For similar materials see Principles of Biology in Biology at University of Arkansas.


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Date Created: 10/14/16
Chapter 25: DNA Structure and Gene Expression Highlight​ = Key Term Highlight​ = Important Concept Virus ● H1N1 influenza virus ○ Spread so fast it was declared a pandemic ○ Occurred in 207 countries ○ Infected 600,000+ people ○ Killed an estimated amount of 20,000 people ● Bind to proteins in a cell membrane ● It inserts its hereditary material (DNA or RNA) into the cell ● It takes the cell over to make more viruses ● It can corrupt the cell’s DNA and cause cancer ● Not considered to be living ● Not cellular ● They evolve Combating Viruses ● Molecular biology ● Study DNA ○ How DNA serves as the basis for hereditary material DNA- Genetic Material ● Alfred Hershey & Martha Chase demonstrated DNA as genetic material, instead of as proteins DNA and RNA ● DNA and RNA are polymers of nucleotides ● They are nucleic acids ● Consist of ​ ong chains (polymers)​​ hemical units (monomers) 4 DNA Nucleotides ● Each type of DNA nucleotide has a different nitrogen containing base ○ Adenine (A) ○ Cytosine (C) ○ Thymine (T) ○ Guanine (G) RNA ● Polymer of nucleotides ● DNA ○ Referring to DNA’s location in the nucleus ● RNA ○ Unlike DNA because 1. Uses the sugar ribose instead of deoxyribose 2. Has nitrogenous base U​ racil​ instead of thymine 3. Is ​single stranded DNA Discovery ● James Watson and Francis Crick used Rosalind Franklin’s work to make their 3D structure of DNA ● The structure consists of​ polynucleotide strands wrapped around each other in a double helix Structure of DNA ● 4 possible bases ○ 2 p​ urines ■ Adenine ■ Guanine ○ 2 p​ yrimidines ■ Thymine ■ Cytosine ● DNA is a polynucleotide strand with a backbone ● 2 strands make up double helix ○ Held together by hydrogen bonds ● Complementary base pairing ○ Adenine → thymine ○ Guanine → cytosine DNA Replication ● Process of c​ opying one DNA double helix into 2 identical double helices ● DNA Polymerase: ​ key enzyme for DNA replication ● Semiconservative Replication: ​ uses each original strand as a template to create a new complementary strand ○ Each daughter DNA molecule consists of one new carbon chain of nucleotides and one from the parent DNA molecule ○ The 2 daughter DNA molecules are identical to the parent molecule DNA Replication 1. Before replication,​ strands of the parent molecule bond together​ through hydrogen bonds 2. Helicase (enzyme DNA) u ​ nwinds the double stranded DNA 3. New complementary DNA nucleotides fit into place​ along separated strands by complementary base pairing. These are joined by DNA Polymerase a. DNA Polymerase leaves parental DNA helix and makes the new strand of DNA 4. DNA ligase seals breaks​ in the sugar-phosphate backbone 5. The 2 double helix molecules are identical to each other and the original molecule Gene Expression ● Using a gene sequence to synthesize a protein ● Depends on the different types of RNA ○ Messenger RNA (mRNA) ○ Transfer RNA (tRNA) ○ Ribosomal RNA (rRNA) ● Depends on 2 processes: ○ Transcription ■ Takes place in nucleus ■ Part of DNA is a template for mRNA formation (to produce a RNA molecule) ○ Translation ■ Occurs in cytoplasm ■ Sequence of mRNA bases determines the sequence of amino acids in a polypeptide ■ tRNA brings amino acids to the ribosome Messenger RNA ● Carries genetic info from DNA ​ o the ribosomes for protein synthesis ● Formed by transcription ● Process begins when RNA Polymerase binds to a promoter (in DNA) ● DNA helix is opened so complementary base pairing can occur ● RNA polymerase joins new RNA nucleotides in a sequence complementary to the DNA ● Uracil replaces thymine ● RNA polymerase keeps making RNA until it reaches the terminator ● Processing of mRNA ● Primary RNA contains bases complementary to both intron and exon segments of DNA ○ Intron:​ segments that get removed ○ Exon: ​ portion of gene that is expressed ● Guanine cap is added to the end Translation ● Creation of proteins from RNA sequence ● Translation requires several enzymes Genetic Code ● Triplet code​ each 3 nucleotides units of mRNA is called a codon ● 64 different mRNA codons ○ 61 code for amino acids ■ Redundant code- some amino acids have numerous code words ■ Provides protection against mutations ■ 3 stop codons signal termination ○ Genetic code is almost universal in all living organisms Transfer RNA ● Transports amino acids to ribosomes ○ Boot-like shape because of base pairing within one strand ○ Amino acid binds to one end, opposite end has an anticodon ○ Triplet of 3 bases complementary to a specific codon of mRNA ● Order of mRNA codons determines which tRNA brings in amino acids Translation ● Ribosomes and Ribosomal RNA ● Ribosomes ○ Exist as free or attached to endoplasmic reticulum ○ Composed of many proteins and ribosomal RNA ○ 2 ribosomal subunits ○ Subunits join just before translation occurs ○ After initial portion of mRNA’s is translated by a ribosome, the ribosome begins to move down the mRNA ○ Other ribosomes may attach to the mRNA ○ Several ribosomes move along the same mRNA ■ Multiple copies of a polypeptide may be made ■ Entire complex is called a polyribosome Translation ● Codons (mRNA) pair with anticodons (tRNA) and carry specific amino acids ○ Order of codons determines the order of tRNA entering the ribosome and sequence of amino acids in a polypeptide ○ Its an orderly process ○ 3 steps: ■ Initiation (require energy) ■ Elongation (require energy) ■ Termination Initiation ● Brings all translation components together ● Initiation factor​ ssemble ribosomal components ○ Small ribosomal subunits (mRNA) initiator (tRNA) and large ribosomal subunit ● Initiator tRNA attaches to start codon (AUG) ● Ribosome has binding sites for tRNA ○ P site (peptide) ○ A site (amino acid) ○ E site (exit) ● Each protein starts with AUG and the amino acid methionine Elongation ● Process where p ​ olypeptide increases in length ● Occurs one amino acid at a time ● 4 steps: 1. A tRNA with peptides a​ ttached is at the P si​ and a tRNA that carries amino acids is arriving in place 2. Once the tRNA is in place at the A site, the peptide chain transferred to tRNA 3. Energy contributes to the peptide bond formation, ​ making one amino acid longer by adding peptide A from the site 4. Translocation occurs-​ mRNA moves forward one codon length and the tRNA is at the ribosomal P site. The tRNA that's been spent exits. New codon is at the A site to receive the next complementary tRNA. Termination ● Final step of protein synthesis ● The new polypeptide and components that carried out protein synthesis are separated from each other. ● Occurs at the stop codon ● Requires release of factor protein to clear the polypeptide from the last tRNA ● Ribosome dissociates into 2 subunits Gene Expression ● Cells differ in structure in function ● Different cell types contain their own specific combination of proteins ● Only certain genes are active in cells that perform specialized functions ○ Nerve, muscle, glands, and blood cells ● Housekeeping genes​ control functions that are common to many types of cells ○ Active in many routine functions ○ Only certain genes are active in cells that perform specialized functions ○ Gene expression controlled in a cell and this control accounts for its specialization Eukaryotes- Gene Expression ● Genes have their own specific promoters ● Different mechanisms to regulate gene expression ○ Affects whether the gene is expressed, ​ the speed with which it is expressed, how long it’s expressed. Levels of Gene Control 1. Pretranscriptional control 2. Transcriptional control 3. Posttranscriptional control 4. Translational control 5. Posttranslational control 1. Pretranscriptional Control ● DNA methylation and chromatin packing keep genes turned off ● Genes located with heterochromatin (darkly staining portions of chromatin) are inactive ○ Barr body in mammalian females ■ Example: tortoiseshell and Calico cat ● Active genes are found in euchromatin​ (loosely packed chromatin) ○ Before it can be transcribed, it must be “unpacked” ○ Chromatin remodeling complex pushes the nucleosome aside 2. Transcriptional Control ● Interactions between certain proteins and certain DNA sequences ○ Proteins called transcription factors and activators ● Transcription factors help RNA polymerase bind to the promoter 3. Posttranscriptional Control ● Primary mRNA is processed b ​ efore learning the nucleus ● Primary mRNA converts to mRNA ○ Addition: poly-A tail and a guanine cap ○ removal: introns and splicing of exons ● Speed of transport for mRNA out of the nucleus affects the amount of gene product occurring after transcription 4. Translational Control ● Longer the m ​ RNA is available in the cytoplasm, the more gene product that’s available for translation ● Differences in p​ oly A tail or guanine caps may determine how long the mRNA is available for translation 5. Posttranslational Control ● After synthesis, some proteins must be activated ○ Example: insulin activated by enzymatic removal of a sequence of 30 amino acids ● Most proteins function for a short amount of time before being destroyed by the cell Gene mutations ● Permanent change in sequence of bases​ in DNA ● Could have none to complete inactivity of the protein Causes of mutations ● Errors in replication ○ These are rare forms of mutations ○ DNA polymerase proofreads and minimizes the error in new strands of DNA ● Mutagens ○ Environmental influences ■ Example: radiation, x-rays, UV radiation ○ DNA repair enzymes constantly monitor and repair irregularities ● Transposons ○ DNA that moves within and between chromosomes ● Viruses ○ Insert their own DNA into their host’s chromosomes ■ HPV- leads to cervical cancer Mutation ​ ffects on protein activity ● Point mutations: ​ change in a single DNA nucleotide ○ Possible outcomes of point mutations: ■ May cause c ​ hange in amino acids ■ No effect ■ Produce a ​ bnormal protein ● Sickle cell anemia ■ Produce i ​ ncomplete protein ● Stop protein placed where an amino acid should be Frameshift Mutations ● One or more nucleotides are inserted or deleted from DNA ● Can result in a completely new sequence of codons ○ Possibly nonfunctional protein Nonfunctional Proteins ● Single nonfunctioning protein can have a dramatic effect on an organism ● Enzymes are typically part of the metabolic pathways ○ If enzyme E iA faulty then phenylalanine can’t be broken down, causing it to build up, causing mental impairment, phenylketonuria. ● Causes white colonies of serratia marcescens Review Questions What enzyme produces mRNA? RNA polymerase What type of RNA has translation in its structure? tRNA This is because of the: ● Amino acid ● Anticodon Different cells in multicellular organisms look different because… All cells have the same DNA with different genes turned on and off. The regulation of gene expression where activator proteins bind to DNA is Transcriptional Control If a strand of DNA read CGTAA, what would be the complementary strand? GCATT


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