Ch 16 and Introduction of Ch 17 This PowerPoint is posted. Replication Transcription Translation Protein!
In the start of things lin the 1950 s scientists knew that chromosomes carry hereditary material and consist of DNA and protein llittle was known about nucleic acids lso is it DNA or protein that is the actual genetic material?
lin 1952, Alfred Hershey and Martha Chase discovered that DNA was the genetic material of a bacteriophage (virus that affects bacteria). lthey tagged viral protein + viral DNA w/ different radioactive isotopes of T2 phages lallowed T2 to infect separate samples of E. coli lcultures were shaken to loosen phages that still didn t get into the bacterial cell
Results: lin tubes with the E. Coli infected with DNA labeled T2, the radioactivity was INSIDE the pellet of the bacteria cells lin tubes with the E. Coli infected with protein-labeled T2, the radioactivity was OUTSIDE (in supernatant) with the viruses
Therefore lviral proteins remained outside ldna was injected in host cell linjected DNA molecules cause cells to produce additional viruses with more viral DNA and proteins
Other Evidence lthere was just something special about DNA: l-a eukaryote cell doubles its DNA content prior to mitosis lduring mitosis, the doubled DNA is equally divided into daughter cells lan organism s diploid cells have twice the amount of DNA than haploids
Characteristics of DNA: lchargaff s rules= A pairs with T and C pairs with G ldna is a double helix with a uniform width of 2 nm. la and G are purines with 2 rings lt and C are pyrimidines with 1 ring lcollectively, H+ bonds stablize DNA structure
Step 1) DNA replication lwatson and Crick proposed that when DNA replicates: l-two DNA strands separate l-each strand is a template for assembling a complementary strand
Replication is lsemi-conservative= each of the two resulting DNA molecules should be composed on one original strand (conserved) while the other is newly created lcomplex lrapid laccurate
Steps to Replication la) Must find a origin of replication. This is where the DNA double helix will open and a replication fork starts. (Bacteria or viral DNA only have 1, but Eukaryotes have thousands)
lb) Strand Separation- Helicases are enzymes which unwind the parental double helix lc) Single-Stranded binding (SSB) proteins stabilize the unwound DNA until new complementary strands can be synthesized
ld) DNA polymerase links the nucleotides to the growing strand. ldna polymerase needs a PRIMER to work. Primase (an enzyme makes primer). l **DNA can only elongate in the 5 to 3 end which causes a problem** (see next slide)
Leading vs. Lagging lthe leading strand is the DNA strand made in the normal 5 to 3 direction llagging strand- DNA strand that is discontinuously synthesized against the overall direction because it is 3 to 5. Lagging strand is produced in short segments called OKAZAKI FRAGMENTS (which are synthesized in the 5 to 3 direction)
Primase making the primer lso we mentioned DNA polymerase needs a primer to work. ltake a guess: lleading strand needs primer(s). llagging strand needs primer(s).
lmismatch repair: Proofreading lthis can correct mistakes while DNA is synthesized. DNA polymerase can do this as well as other proteins. lexcision repair: lover fifty types of DNA repair enzymes can repair damage it is excised. Then DNA polymerase + DNA ligase (glue) fills it in.
Animations ldna Replication is semi-conservative http://www.lewport.wnyric.org/jwanamak ER/animations/DNA%20Replication%20- %20long%20.htm DNA Replication http://www.ncc.gmu.edu/dna/repanim.htm
Lecture Question: Use these words in sequence l Ligase l DNA polymerase l Helicase l Primase l SSB Proteins l Primer l Origin of Replication l DNA Replication:
An example of the work that is done l http://nobelprize.org/educational_games/me dicine/dna_double_helix/
Gene Mutations Gene mutations that involve changes in one or a few nucleotides are called point mutations, because they only occur at a single point in the DNA sequence. These include changes substitutions, insertions, and deletions. Substitutions occur when one base is changed to another. These normally affect no more than one amino acid. Ex. ATG ACG
Frameshift Mutations include insertion and deletion. They are called frameshift because they shift the reading frame of the genetic message. These mutations may change every amino acid that follows the point of mutation. Frameshift mutations can alter a protein so much that it is unable to perform normal functions. Insertion occurs when one base is inserted. These can affect many different amino acids because Ex. ATG CGT ATC GCG T Deletion occurs when one base is deleted from the original sequence. Ex. ATG CGT ATC GT
Chromosomal Mutations Chromosomal mutations involve changes in the number or structure of the chromosome. These change either the location of genes or the number of copies. There are 4 types. Deletion loss of all or part of a chromosome
lduplication produce extra copies of parts of a chromosome
Inversion reverse the direction of parts of the chromosome Translocation part of one chromosome breaks off and attaches to another
Some mutations are neutral meaning they have little or no effect on the expression of genes or the function of proteins for which they code. Others that change protein structure or gene activity are harmful. These are often the cause of genetic disorders and sometimes associated with cancer.
However, some mutations are the source of genetic variability. lplant breeders often take advantage of these mutations. For example, sometimes in meiosis a set of chromosomes fails to separate and produce gametes that are triploid (3N) or tetraploid (4N). This is called non-disjunction. The condition in which an organism has extra sets of chromosomes is called polyploidy. These plants are often stronger and larger.
Next Chapter: Transcription + Translation DNA more DNA (DNA replication) DNA mrna (Transcription) mrna gets matched up with its trnas makes amino acid (Translation)
The Types of RNA lmessenger RNA: carries copies of the instructions for assembling amino acids from the DNA to the rest of the cell; long, single strand of nucleotides
l ribosomal RNA: takes up the major part of ribosomes; involved in protein synthesis l transfer RNA: transfers each amino acid to the ribosome
Transcription ltranscription is the process whereby a sequence of DNA is copied into a complementary sequence of RNA.
During transcription, DNA is unwound and separated by an enzyme called RNA polymerase. lrna polymerase starts making the copy of RNA at specific sites in the DNA known as promoters. lthere are similar places in the DNA that also tell the RNA polymerase to stop. RNA polymerase uses one of the strands to copy the genetic information into a strand of RNA.
l Some parts of the original DNA strand contained sequences of nucleotides called introns that are not involved in coding for proteins. l These must be taken out of the newly made RNA strand. The remaining nucleotides that are involved in coding for proteins are called exons. Now it is ready to go as a mrna molecule!
l DNA is read by RNA and copied into a complementary strand. That strand tells the cell which amino acids to make. na A string of amino acids is known as a protein. Different orders of amino acids make different proteins. mrna
lmrna's instructions are called the genetic code. The genetic code is read three letters at a time, so each word is three bases long. Remember that the bases of RNA are A, U, C, and G; the word is written from these four letters. lthe mrna word that is three bases long is called a codon. A codon is three consecutive nucleotides long and specifies a single amino acid.
TRANSLATION l The order of amino acids is determined by the order of nucleotide bases in an mrna molecule. l The process of reading these nucleotides into a polypeptide chain (a protein made of amino acids) is called translation.
Steps in Translation 1. RNA is transcribed from DNA and released into the cytoplasm 2. mrna attaches to a ribosome. 3. Each codon is read and an amino acid is brought INTO the ribosome by trna. a. The first amino acid to be read is called the start codon because it starts the process of translation. i. AUG: methionine b. Each amino acid has its own specific trna carrier. c. One end of each trna has a specific amino acid and the other end has three unpaired bases. These bases are called the anticodon, and are complementary to three bases on mrna.
Translation Steps Cont. 4. The amino acid is strung together to make a protein inside the ribosome by forming a peptide bond between each amino acid and by being removed from the trna molecule. 5. This process continues until the ribosome reaches a stop codon on the mrna molecule. This signals the process of translation to stop and a complete protein is now formed. a. There are three stop codons: UAA, UAG, and UGA
DONE!! lnow, a protein (chain of amino acids) has been made by using transcription and translation.
Translation Animation! http://www.biostudio.com/demo_freeman_pr otein_synthesis.htm
Questions to Think About Answer these with either transcription or translation 1. Which one should happen in the nucleus (if a eukaryote)? (think about this!) 2. Which one makes mrna? 3. Which one directly makes protein? 4. Which one occurs first? 5. Which one requires RNA polymerase?