Unit 6: structure of DNA (8.2-8.5)

Replication

- process by which DNA is copied

transcription process

1. A large transcription complex made of RNA polymerase and other proteins recognizes the start of a gene and begins to unwind the segments of DNA 2. RNA polymerase uses one strand of the DNA as a template. RNA nucleotides form complementary base pairs with the DNA template. G pairs with C and A pairs with U. the growing RNA strand hands freely as it is transcribed. Then the DNA strand closes back together 3. A completed RNA stand separates from the DNA template and the transcription complex falls apart

Synthesize what might genetics learn about genes by studying RNA?

Because mRNA codes for only a single gene, studying mRNA can help researchers learn where genes begin and end on a chromosome. It could also indicate what genes are active in specific types of cells.

explain the function of replication.

Replication assures that every cell has a complete set of identical, genetic information and make a copy of the DNA so it can be passed to the new cell.

How do cells help ensure that DNA replication is accurate?

Certain types of DNA polymerase had a "built in" proof reading system to correct any errors in the base pairing making it more accurate

Ribosomal RNA (rRNA)

RNA that is the ribosome and guides the translation of mRNA into a protein; also used as a molecular clock

Explain how the double-helix model of DNA built on the on the research of Rosalind Franklin.

Rosalind Franklin used a technique called x-ray crystallography, which shaped the atoms of DNA in a pattern of and X indicating the DNA was, in fact, a double helix molecule.

Infer which part of the DNA molecule carries the genetic instructions that are unique for each individual: the sugar phosphate backbone or the nitrogen containing bases? Explain.

The backbone is the same in all Nitrogen bases. The nitrogen containing bases provide the genetic, unique instructions for each individual.

How are the base-pairing rules related to Chargaff's research on DNA?

The base pairing rule is DNA cytosine pairs with guanine and adenine pairs with thymine always, well Chargaff said adenine is approximately the same amount as thymine and same with cytosine and guanine. These are like the base pairing rules because thymine always goes with adenine and cytosine always with guanine.

Why can the mRNA strand made during transcription be though have as a mirror image of the DNA strand from which it was made?

The mRNA chain is complementary to the DNA molecule but it is not identical to it

synthesize suppose tRNA molecule had the anticodon AGU. What amino acid would it carry?

The tRNA molecule would recognize the mRNA codon UCA, so it would carry the amino acid serine.

How many types of nucleotides are in DNA, and how do they differ?

There are four types of nucleotides in DNA. They differ in their nitrogen-containing bases

RNA (Ribonucleic acid)

a natural polymer that is present in all living cells and that plays a role in protein synthesis

Anticodon

a region of a tRNA molecule that consists of a sequence of three bases that is complementary to an mRNA codon

DNA polymerase

an enzyme that catalyzes the formation of the DNA molecule

RNA Polymerase

an enzyme that starts (catalyzing) the formation of RNA by using a strand of DNA molecule as a template

nucelotide

an organic compound that consists of a sugar, a phosphate, and a nitrogenous bas; the basic building block of a nucleic-acid chain

Start codon

codon that signals to ribosomes to begin translation; codes for the first amino acid in a protein

Stop codon

codon that signals to ribosomes to stop translation

Transfer RNA (tRNA)

form of RNA that brings amino acids to ribosomes during protein synthesis

Codon

in DNA and mRNA, a three-nucleotide sequence that encodes an amino acid or signifies a start signal or a stop signal

What is the central dogma?

it is a statement that summarizes how information flows in one direction from DNA to RNA to proteins

double helix

model that compares the structure of a DNA molecule, in which two stands wind around one another, to that of a twisted ladder

Why might a cell make lots of rRNA but only one copy of DNA?

rRna is a component to of ribosomes, and many ribosomes are needed to keep up with the level of protein synthesis needed by a cell. However, each cell needs only one set of DNA so it is copied only in preparation for cell division

Translation

the portion of protein synthesis that takes place at ribosomes and that uses the codons in mRNA molecules to specify the sequence of

base pairing rules

the rules stating that in DNA cytosine pairs with guanine and adenine pairs with guanine and adenine pairs with uracil (A-T C-G; A-U)

replication process

1. Enzymes begin to unzip the double helix at numerous places along the chromosomes called origins of replication. That is, the hydrogen bonds connecting broken base pairs, the original molecule separates and the bases on each stand are exposed. Like unzipping a suitcase, the process of unzipping DNA proceeds in two directions at the same time 2. One by one, free nucleotide pair with the bases exposed as the template stands unzips. DNA polymerase bonds the nucleotides together and form new stands complementary to each template. On one template, DNA replication occurs in a smooth, continuous way in one direction. This continuous stand is called the leading stand. On the other template, replication occurs in a discontinuous, piece-by-piece way in the opposite direction. Replication of this stand, known as the lagging strands, is not shown or described in detail here. 3. Two identical molecules of DNA result, each one with stand from the original molecule and one new strand. As a result, DNA replication is called semiconservative because one old stand is conserved, and one new strand is made

translation process

1. the exposed codon in the first site attract complementary tRNA bearing an amino acid. The tRNA pairs with the mRNA codon, bringing it very close to the other tRNA molecule 2. the ribosome forms a bond between the two amino acids and breaks the bond between the first tRNA and its amino acid 3. the ribosome pulls the mRNA strand the length of one codon. The first tRNA is shifted into the exit site, where it leaves the ribosome and returns to the cytoplasm to recharge. The first site is again empty by exposing the next mRNA codon.

explain the connection between a codon and an amino acid.

A codon is a sequence of three nucleotides that specifies a specific amino acid. Each tRNA molecule binds to a specific amino acid and has an anticodon that binds to a specific codon.

Explain how DNA serves as its own template during replication.

A new strand of DNA can be synthesized when the other strand is a template to guide the process. Every time the order of the bases is preserved and DNA can be accurately replicated over and over again

Predict in a sample of yeast DNA, 31.5% of the bases are Adenine (A). Predict the approximate percentages of C, G, and T. Explain.

Adenine and thymine are both 31.5% and Guanine and Cytosine are 18.5% because of Chargaff's rule that A and T are approximately the same amount and C and G are approximately the same amount.

DNA is replicated before both mitosis and meiosis. How does the amount of DNA produced in a cell during mitosis compare with that produced during meiosis?

Cell produced in mitosis typically have twice the DNA as cell produced by meiosis

enzymes have shapes that allow them to bind to a substrate. Some types of RNA also form specific three-dimensional shapes. Why do you thin RNA, but no DNA, catalyzes biochemical reactions.

DNA is usually in double-stranded form, wrapped up and condensed to make it compact, not in a catalytic form. In contrast, hydrogen bonds form between the nucleotides if a single strand of RNA, causing it to form a catalytic structure

Summarize describe two major functions of DNA polymerases.

DNA polymerase bonds the nucleotides together and form new strands complementary to each template. DNA polymerase can also detect the error of a wrong nucleotide added to a strand of DNA and fix it.

Infer why is it important that human chromosomes have many origins of replication?

Each Chromosome in a Eukaryotic cell is very long, if replication started at one place, it would take forever to be finished because there are billions of nucleotides per strand of DNA. So multiple origins of replication are needed to make the process go faster.

Messenger RNA (mRNA)

Form of RNA that carries genetic information from the nucleus to the cytoplasm, where it serves as a template for protein synthesis

You know that a healthy cell cannot pass the G checkpoint until its entire DNA has been copied. Do you think that a cell must also transcribe its entire gene into RNA to pass this checkpoint? Explain.

No, because RNA is not being used as a template to get the exact copy of the gene, the point of the RNA is to carry DNA instructions, so it doesn't have to transcribe its entire gene into RNA to pass the checkpoint. Plus, DNA cannot leave the cytoplasm, but the whole point of transcription is to carry the DNA to the process of translation, there is nothing about keeping RNA just in the cytoplasm, nor needing to leave to the process of translation.

4. Apply if a DNA segment has the nucleotides AGCCTAA, What would be the nucleotide sequence of the complementary RNA strand?

UCGGAUU

The DNA of all organisms contains the same four bases (adenine, thymine, cytosine, and guanine.) what might this similarity indicate about life on earth?

We all come from a common ancestor

hypothesize the DNA of eukaryotic cells has many copies of genes that code for tRNA molecules. Suggest a hypothesis to explain why a cell needs so many copies of these genes.

rRNA is critical for making ribosome to carry out protein synthesis. rRNA must be made in sufficient quantities to keep up with a cell's demands for various proteins.

Transcriptions

the process of forming a nucleic acid by using another molecule as a template; particularly the process of synthesizing RNA by using one strand of a DNA molecule as a template

briefly describe how the process of translation is started

the small ribosomal sub-unit binds to the mRNA strand at the start codon, which binds to the first tRNA molecule

Central dogma

theory that states that, in cells, information only flows from DNA to RNA to proteins