Topic 1 ; the molecular basis of inheritance Flashcards Preview

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Who discovered the double helix structure and in what year?

James Watson and Francis Crick in 1953


What does nucleotides consist of ?

Deoxyribose (5 carbon sugar), phosphate groups and a base (nitrogenous compound).


What are the four bases of DNA?

Adenine, thymine, guanine and cytosine


Which base pairs with which?

A with T and G with C


What does the information within DNA do?

Guides the cell in making new proteins along with RNA that determine our biological traits.
Gets passed or copied from one generation to the next.


What are the two classes of nitrogen bases called?

Purines (double-ringed structures) and Pyrimidines (single ringed structures).


What does the sides of the DNA ladder consist of?

Sugar-phosphate portions of adjacent nucleotides bonded together. The phosphate of one nucleotide is covalently bonded to the sugar of the next nucleotide.


What causes the DNA structure to twist?

The hydrogen bonds between phosphates.


Explain the location of 5' and 3'.

The 5' prime (-OH, where a free phosphate group is attached to deoxyribose sugar) carbon is located at the top of the leading strand and the 3' prime (OH group which is where a free hydroxyl group is attached to a deoxyribose sugar) carbon is located at the lower section of the lagging strand.


Explain the anti parralel situation in the double helix structure.

The nucleotide sequences are coplementary and parallel, but they go in opposite direction. Antiparallel means the two DNA strands are arranged in the opposite direction. This structure is important in DNA replication because it replicates the leading strand one way and the lagging stand the other way.


If drawn diagrammatically, the two DNA strands will look like:



Explain complementary.

Because A always pairs with T and G always pairs with C, the order of the bases on one strand dictates the order of the bases on the other strand. Hence one chain is the complement of the other. It is important to realize the two chains are NOT the same.


What does 5' and 3' mean?

Refers to the carbons on the sugar.


When a cell reproduces, where does all the information go?

To the daughter cells.


In prokaryotes, where does DNA replication take place?

In the cytoplasm.


In eukaryotes, where does DNA replication take place?

In the nucleus.


What is semi-conservative replication?

Semiconservative replication would produce two copies that each contained one of the original strands and one new strand.


What is a replication fork?

The replication fork is a structure that forms within the nucleus during DNA replication. It is created by helicases, which break the hydrogen bonds holding the two DNA strands together. The resulting structure has two branching "prongs", each one made up of a single strand of DNA. These two strands serve as the template for the leading and lagging strands, which will be created as DNA polymerase matches complementary nucleotides to the templates; the templates may be properly referred to as the leading strand template and the lagging strand template.


What is the leading strand?

The leading strand is the strand of nascent DNA which is being synthesized in the same direction as the growing replication fork. A polymerase "reads" the leading strand template and adds complementary nucleotides to the nascent leading strand on a continuous basis.


What is the lagging strand?

The lagging strand is the strand of nascent DNA whose direction of synthesis is opposite to the direction of the growing replication fork. Because of its orientation, replication of the lagging strand is more complicated than that of the leading strand.

The lagging strand is synthesized in short, separated segments. On the lagging strand template, a primase "reads" the template DNA and initiates synthesis of a short complementary RNA primer. A DNA polymerase extends the primed segments, forming Okazaki fragments. The RNA primers are then removed and replaced with DNA, and the fragments of DNA are joined together by DNA ligase.


What is DNA replication and why does it occur?

DNA replication is the process of producing two identical replicas from one original DNA molecule.It occurs because when we divide, we need enough DNA to pass to daughter cells.


Explain the DNA replication process.

1. DNA gyrase (enzyme) makes a nick in the double helix and each side seperates.
2. Helicase (enzyme) unwinds the double stranded DNA.
3. Several small proteins called single strand binding proteins temporarily bind to each side and keep them seperated.
4. DNA polymerase walks down the DNA strands and adds new nucleotides to each strand. The nucleotides pair with the complementary nucleotides on the existing strand.
5. A subunit of the DNA polymerase proofreads the new DNA.
6. DNA ligase (enzyme) seals up the fragments into one long continuous strand.
7. The new copies automatically wind up again.


What are Okazaki fragments?

Short, newly synthesized DNA fragments that are formed on the lagging template strand during DNA replication. They are complementary to the lagging template strand, together forming short double stranded DNA sections.


What is transcription?

DNA never leaves the nucleus (in eukaryotes) so the information must be copied. It is the first step of gene expression, in which a particular segment of DNA is copied into RNA by the enzyme RNA polymerase.


What is mRNA?

Messenger RNA (mRNA) is a large family of RNA molecules that convey genetic information from DNA to the ribosome, where they specify the amino acid sequence of the protein products of gene expression.


Which enzyme is responsible for performing transcription?

RNA polymerase.


How does RNA polymerase make mRNA?

1. Binds to the DNA strand at a specific sequence of the gene called a promotor.
2. Unwinds and unlinks the two strands of DNA
3. Uses one of the DNA strands as a guide or template.
4. Matches new nucleotides with their components on the DNA strand
5. Binds these new RNA nucleotides together to form a complementary copy of the DNA strand (mRNA).
6. Stops when it encounters a terination sequence of bases


What is a promotor?

In genetics, a promoter is a region of DNA that initiates transcription of a particular gene. Promoters are located near the transcription start sites of genes, on the same strand and upstream on the DNA (towards the 5' region of the sense strand). Promoters can be about 100–1000 base pairs long.[1]


mRNA is happy to live in a what state?

single stranded


First step of transcription:

One or more sigma factors (protein needed for RNA synthesis) initiate transcription of a gene by enabling binding of RNA polymerase to promotor DNA.