AP bio unit 6 main topics

major events of transcription

1. Initiation: RNA polymerase binds to DNA at a specific sequence of nucleotides called the promoter. The promoter contains an initiation site where transcription of the gene begins. RNA polymerase than unwinds DNA at the beginning of the gene. 2.Elongation: Only one of the unmound DNA strands acts as a template for the RNA synthesis. RNA polymerase can only add nucleotids to the 3' end of the strand so like DNA, RNA must be synthesized in the 5' to 3' direction. Free ribonucleotides triphosphates from the cytoplasm are paired up with their commplementary base on the exposed DNA template. RNA polymerase joins the ribonucleoside triphosphates to form an mRNA strand. As RNA polymerase advances, the process continues. The DNA that has been transcribed, re-winds to form a double helix. Termination: RNA polymerase continues to elongate until it reaches the terminator, a specific sequence of nucleotides that signals the end of transcription. Transcription stops and mRNA polymerase and the new mRNA transcript are released from DNA. The DNA double helix reforms. The termination sequence usually consists of a series of adjancent adenines preceded by a nucleotide palindrome. This gives an RNA molecule that assumes a stem-and loop configuration. This configuration stops RNA polymerase from transcribing any further.

major steps of replication

1. initiation, 2. elongation, 3. termination

role of repressor genes in operons

A DNA-binding repressor blocks the attachment of RNA polymerase to the promoter, thus preventing transcription of the genes into messenger RNA. An RNA-binding repressor binds to the mRNA and prevents translation of the mRNA into protein. This blocking of expression is called repression.

elongation

DNA polymerases are responsible creating the new strand by a process called elongation. DNA polymerase III binds to the strand at the site of the primer and begins adding new base pairs complementary to the strand during replication. replication proceeds in the 5' to 3' direction

Hershey and Chase

Hershey and Chase studied bacteriophage, or viruses that attack bacteria. proved DNA is transforming agent

how mutations can change the amino acid sequence of a protein

Missense mutation This type of mutation is a change in one DNA base pair that results in the substitution of one amino acid for another in the protein made by a gene. Nonsense mutation A nonsense mutation is also a change in one DNA base pair. Instead of substituting one amino acid for another, however, the altered DNA sequence prematurely signals the cell to stop building a protein. This type of mutation results in a shortened protein that may function improperly or not at all. Insertion An insertion changes the number of DNA bases in a gene by adding a piece of DNA. As a result, the protein made by the gene may not function properly. Deletion A deletion changes the number of DNA bases by removing a piece of DNA. Small deletions may remove one or a few base pairs within a gene, while larger deletions can remove an entire gene or several neighboring genes. The deleted DNA may alter the function of the resulting protein(s). Duplication A duplication consists of a piece of DNA that is abnormally copied one or more times. This type of mutation may alter the function of the resulting protein. Frameshift mutation This type of mutation occurs when the addition or loss of DNA bases changes a gene's reading frame. A reading frame consists of groups of 3 bases that each code for one amino acid. A frameshift mutation shifts the grouping of these bases and changes the code for amino acids. The resulting protein is usually nonfunctional. Insertions, deletions, and duplications can all be frameshift mutations.

termination

Once both the continuous and discontinuous strands are formed, an enzyme called exonuclease removes all RNA primers from the original strands. These primers are then replaced with appropriate bases. DNA ligase joins Okazaki fragments together forming a single unified strand. The ends of the parent strands consist of repeated DNA sequences called telomeres.

difference between replication, transcription and translation

Replication is the process by which DNA polymerase uses DNA as a template to make more DNA. This typically copies the entirety of both strands of a DNA molecule to make two new molecules of double stranded DNA. Copying relies on the complementarity of DNA bases -- A pairs with T and G pairs with C, so that each new double stranded molecule contains the same sequence of base pairs, even though each has a different newly synthesized strand. Transcription is the process by which an RNA polymerase uses DNA as a template to make RNA. This produces a single stranded product that spans only a tiny fraction of an entire DNA molecule. Also, RNA polymerases are slightly more error-prone than DNA polymerases. This too makes use of base pairing for synthesis, with the added wrinkle that RNA uses uracil (U) in place of thymine (T). Translation is the process by which the ribosome uses RNA as a template to make protein. This also requires base-pairing to read the information in the RNA molecule. Transfer RNAs (tRNAs) associate each of the twenty amino acids (protein building blocks) with a defined family of three-nucleotide sequences by physically coupling an amino acid with a short region of RNA that can base pair. The ribosome checks to make sure that the "correct" tRNA is associating with a 3-nucleotide stretch of the template RNA. If things check out, the ribosome catalyzes the addition of the next amino acid to a growing peptide. Of the three processes in this question, this is the only one that doesn't make more nucleic acid.

functions of the 3 parts of an operon

Repressor Gene - Produces a repressor protein that fits in the operator to turn the operon off Promoter - RNA polymerase attaches here to begin transcription of the genes Operator - The active repressor fits in notches to block RNA polymerase and turn off transcription.

general differences between the bacterial chromosomes and eukaryotic chromosomes

Shape: Prokaryotes:Un-coiled- circular in shape Eukaryotes: Coiled- More complex, coiled up in a rod shape. Number: Prokaryotes: Only 1 Chromosome Eukaryotes: More than one chromosome. Location: Prokaryotes: Chromosome attached to the cell membrane Eukaryotes: Chromosomes found in nucleus

steps to translation

The ribosome binds to mRNA at a specific area. The ribosome starts matching tRNA anticodon sequences to the mRNA codon sequence. Each time a new tRNA comes into the ribosome, the amino acid that it was carrying gets added to the elongating polypeptide chain. The ribosome continues until it hits a stop sequence, then it releases the polypeptide and the mRNA. The polypeptide forms into its native shape and starts acting as a functional protein in the cell.

translation

Translation is the final step on the way from DNA to protein. It is the synthesis of proteins directed by a mRNA template. The information contained in the nucleotide sequence of the mRNA is read as three letter words (triplets), called codons. Each word stands for one amino acid.

how DNA packaging can affect gene expression

When DNA is tightly packed around the histones, there is no way for replication to occur. Enzymes like DNA helicase and other proteins cannot have access to the DNA binding site because they are completely hindered. Tightly package DNA (aka chromatin) is transcriptionally inactive which causes certain genes not to be expressed. Loose packaging makes the genes more transcribable. Replication and gene expression are not related.

Avery, MacLeod, and Mc Carty

began with large cultures of heat-killed S cells; results all pointed to DNA as the likely transforming principle. However, Avery was cautious in interpreting his results.

Watson, Crick, Wilkins, and Franklin

codiscovered the double-helix structure of DNA, which formed the basis for modern biotechnology. Franklin obtained images of DNA using X-ray crystallography, an idea first broached by Wilkins. Franklin's images allowed James Watson and Francis Crick to create their famous two-strand, or double-helix, model.

the structure of DNA

double helix structure as a ladder, the phosphate and sugar molecules would be the sides, while the bases would be the rungs. The bases on one strand pair with the bases on another strand: adenine pairs with thymine, and guanine pairs with cytosine.

role of gene regulation in embryonic development and cancer

embryonic development- fertilized egg gives rise to many different cell types- organized successively into tissues, organs, organ systems, and whole organism Gene expression orchestrates developmental programs of animals Embryonic Development: transformation from zygote to adult results from cell division, cell differentiation, and morphogenesis Totipotent stem cells- total potential to form fetus, placenta, etc.

how eukaryotic cells modify RNA after transcription

even after a gene has been transcribed, gene expression can still be regulated at various stages. Some transcripts can undergo alternative splicing, making different mRNAs and proteins from the same RNA transcript. Some mRNAs are targeted by microRNAs, small regulator RNAs that can cause an mRNA to be chopped up or block translation. A protein's activity may be regulated after translation, for example, through removal of amino acids or addition of chemical groups.

transcription

first step of gene expression, in which a particular segment of DNA is copied into RNA by the enzyme RNA polymerase. Both DNA and RNA are nucleic acids, which use base pairs of nucleotides as a complementary language.

impact of DNA methylation and histone acetylation on gene expression

histone acetylation- acetyl groups attached to positively charged lysines in histone tails; loosens chromatin structure, promoting initiation of transcription addition of methyl groups- DNA methylation- tends to condense chromatin, restricting transcription. addition of phosphate groups (phosphorylation) next to methylated amino acid can loosen chromatin

gene expression

process by which information from a gene is used in the synthesis of a functional gene product.

initiation

the double stranded molecule must be "unzipped" into two single strands by DNA helicase