Biology Test 2/22/23

What is Griffiths transforming principle?

* Griffith experimented with the bacteria that cause pneumonia.
* He used two forms: the S form (deadly) and the R form (not deadly).
* A transforming material passed from dead S bacteria to live R bacteria, making them deadly.

What did Avery do with the transforming principle?

* Avery isolated and purified Griffith’s transforming principle.
* Avery performed three tests on the transforming principle.

What were the 3 tests that Avery did?

* Qualitative tests showed DNA was present.
* Chemical tests showed \n the chemical makeup \n matched that of DNA.
* Enzyme tests showed \n only DNA-degrading \n enzymes stopped \n transformation.

How did Hershey and Chase confirm hat DNA is the genetic material?

* Hershey and Chase studied viruses that infect bacteria, or bacteriophages.
* Bacteriophages take over a bacterium’s genetic machinery and direct it to make more viruses.

Is the genetic material made of DNA or protein?

* By discovering which part of a phage (DNA or protein) actually entered a bacterium, they could answer this question once and for all.
* Protein contains sulfur but very little phosphorus, while DNA contains phosphorus but no sulfur.
* They tagged viral DNA  with radioactive  phosphorus.
* They tagged viral proteins with radioactive sulfur.
* Tagged DNA was found inside the bacteria; tagged proteins were not found inside the bacteria.

What is DNA?

* DNA is a long polymer of repeating monomers called __nucleotides__

What is DNA made of?

-A phosphate group

   - A ring shaped sugar called __deoxyribose__

   - A nitrogen base

What is the backbone of DNA?

This ribbon like part represents the phosphate groups and deoxyribose sugar molecules that make up DNA's "backbone."

\
The nitrogen-containing bases bond in the middle to form the rungs of the DNA ladder.

What are nucleotides

* One molecule of human DNA contains billions of nucleotides, but there are onl__y four types of nucleotides in DNA__ .
* The __only difference__ among them are the __nitrogen bases__.

What are the four bases?

* Adenine (A)
* Guanine (G)
* Thymine (T)
* Cytosine (C)

A and G have a?

Double ring structure

T and C have a?

Single ring structure

A and G are classified as?

Purines

T andC are classified as a?

Pyrimidine

What is Chargaffs rule

A=T, C=G

Rosalind Franklin did?

Produced x-ray photographs of DNA that indicated it was a helix. Her coworker, Maurice Wilkins, showed the data without Franklin's consent to Watson and Crick, which helped them discover DNA's structure.

Watson and Crick did?

Used a model to figure out DNA's structure. Their model was influenced by data from other researchers.

What is a double helix?

* Who discovered the "shape" of DNA? 
* __Double helix__ means that two strands of DNA wind around each other like a __twisted ladder__. 
* __Sugar & phosphate__ make the backbone of DNA
* Nitrogen bases makes the rungs (middle part)

What is base pairing?

* In DNA the amount of __adenine__ approximately equals the amount of __thymine__. Same for cytosine and guanine. 
* __Chargaff's rules states:__

           __A pairs with T__ and __C pairs with G__

What are DNA nucleotides of a single strand joined together by?

Covalent bonds

What are double helix held together by?

Hydrogen bonds

G & C have how many hydrogen bonds?

3

A & T have how many hydrogen bonds?

2

What is the process of DNA replication?

DNA replication is the process by which a molecule of DNA is duplicated. When a cell divides, it must first duplicate its genome so that each daughter cell winds up with a complete set of chromosomes.

During that process of cell division, all of the information in a cell has to be copied, and it has to be copied perfectly. And so DNA is a molecule that can be replicated to make almost perfect copies of itself.

How does replication copy the genetic information?

* According to the rules of base pairing, A pairs with T and C pairs with G. (Chargaff’s rules).
* If the base sequence of one strand of DNA is known, the sequence of the other strand is also known. One strand can act as a template, or pattern, for another strand.
* During the process of replication, a cell uses both strands of DNA as templates to make a copy of the DNA.
* DNA does not copy itself; enzymes and other proteins do the work of replication. Replication uses DNA polymerases which are molecules specifically dedicated to just copying DNA.

Where does replication occur?

* Occurring during the S phase of the cell cycle.
* Takes place in the nucleus.

What is the replication rate?

* About 50 nucleotides are added every second, but even then DNA replication would take many days.
* Because of the multiple origins of replication it takes about 8 hours.

Copying DNA is called?

DNA replication

How is DNA replicated?

* DNA is replicated by using strands of DNA, it serves as a template or pattern for new strands.

What is a DNA strand?

* DNA is called __*semiconservative*__ meaning that each DNA double helix contains one parent (old) strand and a new strand.

What is an origin of replication?

Some enzymes pull apart, or unzip, the double helix to separate the two strands of DNA. Other proteins keep the strands apart while the strands serve as template.

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* An enzyme makes a cut and creates many __origins of replication__
* This is where replication begins.
* A group of enzymes called DNA polymerases bond the new nucleotides together.
* When the process ends, there are two complete molecules of DNA, each exactly like the original d

What are replication forks?

* __Replication forks__ are the “Y” shaped region that forms where the parental strands of DNA begin to unwind.
* The forks are created by an enzyme called __helicase__ that cuts the hydrogen bonds.

What are DNA polymerase

* A group of enzymes that bond new nucleotides together.
* Helps proofread the DNA strand and fixes any mistakes.
* Only works in a 5' to 3' direction.

What are SSB proteins?

* __Single strand binding proteins (SSB)__ will __temporarily bind__ to each separated strand and __prevent them from re-pairing__. 

What is RNA primer?

* __RNA primers__ are short strands of RNA that are placed down __before__ DNA polymerase can start replicating. They are added by __RNA primase__
* RNA primers play a key role in DNA replication. Ribonucleic acid (RNA) primers play an essential role in deoxyribonucleic acid (DNA) replication, the copying of DNA molecules that occurs in all living organisms.
* Replication allows an organism to pass on genetic information, contained in a copy of its DNA, to its offspring.

What is a leading strand?

* Strand that is made in a continuous motion. This means that it grows continuously, without any gaps.  
* 5' to 3' direction 
* Follows the helicase; it does not require DNA ligase for its growth.
* Made by the DNA polymerase

What is a lagging strand?

Lagging Strand: replicated strand of DNA formed by short segments (Okazaki fragments).

*  Works slower because it works __away__ from the replication fork.
* DNA polymerase lays down __short fragments of nucleotides__ (100-200) called __Okazaki fragments__
* __Fragments are later "glued" together by an enzyme called DNA ligase.__ 


* Runs 3’ to 5’

Comparing Lagging strands and leading strands

1. __Leading strand__

* It is the new strand of DNA that grows continuously.
* No fragments are seen during the synthesis of a leading strand.
* The direction of growth of the leading strand is 5′→3′.
* Only a single RNA primer is required for the whole leading strand to synthesize.

__2. Lagging strand__

* It is the new strand of DNA that grows discontinuously.
* Various fragments are seen during the synthesis of a lagging strand. These fragments are called Okazaki fragments.
* The direction of growth of the lagging strand is 3′→5′.
* The starting of each Okazaki fragment requires a new RNA primer.

What is Termination?

* Last step of replication
* When DNA polymerase reaches the end of the strands and stops. 
* Termination of DNA replication occurs when two oppositely orientated replication forks meet and fuse, to create two separate and complete double-stranded DNA molecules.