Biology DNA

why do bacteria need operons?

Bacterial genes are organized into operons, or clusters of coregulated genes. In addition to being physically close in the genome, these genes are regulated such that they are all turned on or off together. Grouping related genes under a common control mechanism allows bacteria to rapidly adapt to changes in the environment.

Steps in Replication

1. Two DNA strands are separated by an enzyme 2. Another type of enzyme (DNA polymerase) attaches to each single strand 3. DNA polymerase finds a complementary nucleotide 4. DNA polymerase moves to the next position for another complementary nucleotide 5. The two nucelotides are covalently bonded together 6. The process repeats at the third position 7. The process repeats until two double-stranded DNA molecules are completed.

frameshift mutation

A mutation that adds a single nucleotide and consequently changes the entire production of amino acids after the point

operator vs repressor

A protein in which its binding to the operator inhibits the transcription of one or more genes Repressor proteins can be DNA- or RNA-binding: •DNA-binding repressors - block the binding of RNA polymerase to the promoter. As a result, the gene is prevented from being transcribed into mRNA •RNA-binding repressors - bind to mRNA, preventing protein translation

operator

A specific DNA nucleotide sequence where transcriptional regulatory proteins can bind. repressor proteins bind to this DNA sequence in the operon of prokaryotes.

What are the possible anticodons that you would find on tRNA that has a phenylalanine attached to it (hint look at 10.8A for codons for phenylalanine)

AAA AAG

What is one codon for Arginine? Leucine? Gluatamic Acid?

AGA CUU GAA

Transcription

DNA is used as a template (instructions or blue print) for making RNA RNA is synthesized on a DNA template. In eukaryotes it occurs in the nucleus and the tRNA must travel from the nucleus to the cytoplasm

UAG is the stop codon close to the end of a long chain of nucleotides. What might happen if the uracil in this codon was changed to cytosine

It would no longer be a stop code so the ribosome would continue down to mRNA. The protein would not be correct (and probably would not work). It will add glutamine to the protein chain at this point.

Analogies using 3 letter words (shows difference between point and frameshift mutation

Original ONE FAT CAT AND DOG Point ONE FAT HAT AND DOG Frame ONE FAT HHA TAN DDOG

point mutation vs frameshift mutation

Point mutation results from a single nucleotide change (i.e. switching an A to a T), where as a frameshift mutation is an insertion or deletion which causes the whole amino acid sequence to change. After a frameshift mutation all codons after it will be incorrect.

Translation

RNA is used as instructions for making a protein by the ribosomes Translation can be divided into 4 steps: When polypeptide is complete, the two ribosomal subunits come apart and tRNA and mRNA is released. Translation is rapid; a single ribosome can make an average sized polypeptide in less than one minute. mRNA molecule is translated simultaneously by a number of ribosomes. Steps: Initiation of polypeptide synthesis, elongation, termination

promoter

RNA polymerase binds to this DNA sequence A specific nucleotide sequence of DNA where RNA polymerase binds and initiates inscriptions.

What are all the codons that code for serine

UCU, UCC, UCA, UCG, AGU, AGC

mutation

a change in the nucleotide sequence of DNA

regulatory gene

a gene that codes for a repressor protein a gene that produces a repressor substance that inhibits an operator gene

operon

a group of genes that have a shared operator and promoter A unit of genetic function common in bacteria and phages, consisting of coordinately regulated clusters of genes with related functions.

mutagen

a physical (such as xrays) or chemical agent that causes mutations

capsid

a protein coat around a virus

activator

a protein that turns a gene on by assisting RNA polymerase

gene

a section of DNA that codes for one protein ******Genes serve as a template. It dictates transcription of a complementary sequence of nucleotides in mRNA. The mRNA dicates the linear sequence of the amino acids in specific polypeptide. The proteins that form from the polypeptides determine the appearance and the capabilities of the cell and the organism.********* Genes control the structures and activities of the cells, or more broadly, the way the genotype produces the phenotype.

anticodon

a sequence of 3 nucleotides forming a unit of genetic code in a tRNA molecule, corresponding to a complementary codon in a mRNA molecule. Triplet of bases on side of tRNA

lysogenic cycle

a series of stages in a virus where it inserts its DNA into a host and allows it to divide a viral reproductive cycle in which the viral DNA is added to the host cell's DNA and is copied along with the host cell's DNA Does not destroy the host cell

lytic cycle

a series of stages in a virus where it takes over a cell without delay A type of viral replication cycle resulting in the release of new viruses by lysis (breaking open) of the host cell.

base insertion

a type of gene mutation in which a nucleotide is inserted usually has disastrous effects. Because mRNA is read as a series of nucleotide triplets (codons) during translation, adding or subtracting nucleotides may alter the reading frame of the message. All the nucleotides that are downstream of the insertion or deletion will be regrouped into different codons. Will probably result in nonfunctional polypeptide.

importance of replication

allows each daughter cell to have a copy of its DNA

DNA wraps around itself in a

double helix

difference between point mutation and a frameshift mutation

in a frameshift mutation, bases are added or deleted and many amino acids are changed. in a point mutation, only one bade is changed and only one amino acid is changed.

Why are viruses bad

infectious particles consisting of nucleic acid enclosed in a capsid (protein coat). Viruses are parasites that can reproduce only inside cells.

What are the 3 components of a nucleotide

phosphate group (phosphorous atom and 4 oxygen atoms) 5 carbon sugar (deoxyribose) nitrogenous bases (purines including adenine and guanine, pyrimidines including thyine and cytosine)

repressor

protein that binds to DNA and blocks transcription of a gene.

prophage

the DNA of a virus that is inserted into the host's DNA.

genotype

the genetic makeup of an organism

gene expression

the process by which a gene causes a change in phenotype

mutagenesis

the production of mutation can occur because of error during DNA replication or recombination (spontaneous mutation) or a physical or chemical agent (mutagen).

reading frame

the set of codons that are translated. there are three possible reading frames in DNA

phenotype

the traits of an organism that can be observed

The bonds between nucleotides on the same strand are....

very strong covalent bonds

The bonds between nucleotides on different strands are ...

weak hydrogen bonds

A certain gene has the following sequence: GACAAGTCCACAATC 1, Write the sequence of the mRNA molecule transcribed from the gene 2, Using the genetic cod, write the amino acid sequence if you read the RNA from left to right 3. Write the amino acid sequence if the mRNA molecule is read backwards (from right to left) 4. Why did 2 and 3 give different polypeptides? The mRNA molecule is only read in one direction for this reason

1.CUGUUCAGGUGUUAG 2. LEU, PHE, ART, CYS, STOP 3. ASP, CYS, GLY, LEU, VAL 4. The order of the bases in the codon changes

How many amino acids can 2 nucleotides in a row code for:

16 (hint how many different combinations are possible with 2 nucleotides in row)

Original Strand 5'A-C-G-T-T-A-T-G-C-G-G 3' What does the new strand look like (replication)

3' DNA Polymerase T-A-C-G-C-C 5'

A certain protein is made up of 100 amino acids. What is the smallest number of bases in the messenger RNA molecule that is needed to carry the code for the synthesis of this protein?

300 (30d for the stop codon)

How many amino acids can 1 nucleotide code for:

4 (hint: how many nucleotides are there)

How many amino acids can 3 nucleotides in a row code for:

64 (hint how many different combinations are possible with 3 nucleotides in a row)

Which amino acid does a start or initiator codon code for" How many other codons code for this particular amino acid

??????

codon

A 3 nucleotide sequence in mRNA that specifies a particular amino acid or polypeptide termination signal; the basic unit of genetic code A three-nucleotide sequence of DNA or mRNA that specifies a particular amino acid or termination signal; the basic unit of the genetic code. Significance: Once the start codon emerges from the first ribosome, a second ribosome can attach to it; and several ribosomes may trail along on the same mRNA molecule. Each polypeptide coils and folds, froming a 3d shape (tertiary structure). Several of them may come together forming a protein with a quaternary structure.

point mutation

A change in a gene at a single nucleotide pair. single change in a nucleotide that can make an incorrect protein. Can result in premature or late stop codon and can change the amino acid

phosphate group

A functional group consisting of a phosphorus atom covalently bonded to four oxygen atoms

where does replication occur?

cell's nucleus

Replication

copying DNA. Cells copy their DNA before dividing into two new cells so that each daughter cell gets a copy

why is translation important

creates the protein by linking together amino acids.

where does transcription occur?

cytoplasm of the cell

what are the main parts of a nucleotide?

deoxyribose or ribose purines or pyrimidines nitrogenous base

what are the three types of RNA and what are their functions?

mRNA - messenger tRNA - transfers amino acids to ribosomes rRNA - forms ribosomes that build proteins

importance of transcription

makes mRNA, which carries instructions for making proteins. DNA cant do this because it is too big to leave the nucleus.

base substitution

replacement of one nucleotide with another. leads to an improved protein that enhances the success of the mutant organism and its descendants. Depending on how the base substitution is translated, it can result in no change in the protein, an insignificant change, or a change that can significantly affect the organism. Because of the redundancy of the genetic code, some substitution mutations have no effect. Other changes of a single nucleotide may alter an amino acid but have little effect on the function of the protein. Base substitutions may cause changes in a protein that prevent it from functioning normally. If it changes an amino acid codon to stop codon: a shortened, probably nonfunctional polypeptide will result

where does translation occur?

ribosomes