Cell and Molecular Biology - Genetics Unit Exam 1

Genetic material must contain:

1.) complex information 2.) replicate faithfully 3.) encode the phenotype 4.) have the capicity to vary

What did Kossel do?

He discovered the nitrogenous bases, AGTC

What did Leverne do?

He identified nucleotides as the encoders for genetic material

Who was Griffith and what were his experiments?

He was the scientist who discovered that there was a carrier of genetic material, he found this out by using virulent bacteria and non-virulent bacteria and injecting into the mice following heat treatment to see if the mouse dies. This also introduced the idea of transformation. 

What is transformation in bacteria?

When bacteria take up things from their environment, like genetic material

What did Avery, MacLead, and McCarty do?

Utilized the transforming principle and added enzymes that killed proteins and RNA, they then found mice still died so they could figure out DNA was the thing that was introducing the virus so they knew DNA was carrying it.

What did Hershey-Chase experiments do?

These experiments tagged DNA was phosphorous isotopes (radioactive) with bacteriophages and cultured samples with radioactive and non-radioactive phages. They could then see if DNA was conserved by seeing the presence of radioactivity in the cultured samples.=

Is DNA the only carrier of genetic information?

No, RNA is also a source of genetic information (Fraenkel-Conrat and Singer’s experiment showed this in the tobacco mosaic virus.

What are the 3 major components of a nucleotide structure?

1.) phosphate group 2.) a sugar base 3.) a nitrogen base

When it comes to the sugar base of RNA and DNA, what is a major difference?

At carbon 2,  RNA has an OH group while DNA has a H group

When nucleotides are linking to each other, where and what are the linkage points?

At the phosphate group, the double bonded oxygen. At the sugar base, the HO group.

In terms of 5’ and 3’ where are phosphate groups and sugar bases located?

5’ always has a phosphate and 3’ always has a sugar base

What is Chargaff’s Rule?

A=T and G=C and (A+G)/(C+T)=1

What are the 3 forms of DNA and what separates them?

B-DNA: the typical formation, has the major and minor groove and is the most stable conformation

Z-DNA: left spiral, longer stretches of C and T

A-DNA: shorter and wider conformation of the typical B-DNA

What is methylation and how does it impact DNA?

Methylation occurs when a methyl group is added to a base and it changes the secondary structure of DNA, occurs almost exclusively in the cytoplasm

What is supercoiling and why does it occur?

Supercoiling is when DNA is bound up into smaller packages in order to conserve space

How does supercoiling occur?

Supercoiling occurs using topoisomerases, they also relax supercoils back into circular DNA.

What is the difference between type 1 and type 2 topoisomerases?

Type 1: single cuts Type 2: double cuts

What is denaturing and what factors impact temperature of denaturation?

Denaturing of double stranded and renatured at specific temperature, the more double bonds A and T means lower denaturing temp. 

What is a nucleosome?

8 histone molecules and linker DNA from H1 to histone tail.

When in the cell cycle does DNA replication take place?

All genetic information is duplicated (mitosis) and divided equally among daughter cells and the actual replication takes place in the S phase of interphase.

What is meant by semiconservative replication?

This is when ½ of each strand is retained as the template strand in each daughter cell.

What experiment showed semiconservative replication?

Melson-Stahl experiment with E.coli and N15 media (heavier) and N14 media (lighter). When replicated it showed different levels of weight which shows some N15 is conserved in replication.

What are the 3 requirements of replication?

1.) template consisting of single stranded DNA

2.) raw materials

3.) enzymes and proteins

What is directionality and how does it apply to DNA replication?

DNA synthesis and replication requires on different components working in different directions. If working in circular DNA, DNA replication will occur bidirectionally. 

What direction does DNA synthesis occur in?

5’ to 3’ direction

In bacteria, what is the origin of replication called and how is it identified?

OriC and it is identified by the presence of several consensus sequences tandem repeats. Specifically, 3 13-Mers and 4 9-Mers in bacterial species.

What are the 4 steps of replication in bacteria?

1.) initiation

2.) unwinding

3.) elongation

4.) termination

What are the primary steps of initiation in bacteria replication?

1.) initiator proteins bind to the OriC (specifically the 9-mers bind and the 13-mers open up the DNA)

2.) single stranded binding proteins bind to the small unwo

DNA packaging in eukaryotes has a few distinct features in comparison to prokaryotes, what are the 3 main differences?

1.) multiple, linear DNA molecules that are complexed with histones

2.) stored within the nucleus

3.) organelles are membrane bound

What is a telomere and what is it’s importance?

A DNA sequence at the end of a chromosome, acts kind of like an eyelet of a shoe lace and keeps the chromosome from unraveling.

How can we identify chromosomes?

A process called G-banding, relies on a phenotypic pattern

What are the different types of DNA sequences?

• Unique

• Repetitive

  • tandem

  • interspersed

• Highly repetitive

Where are some other places that distinct DNA can be found and what theory does the presence of DNA support?

There is DNA found within the mitochondria and chloroplast, specifically a double-stranded DNA. This is evidence for endosymbiotic theory and is typically uniparentally inherited like mitochondrial DNA comes from the mother.

What is the basic structure of the nucleus?

Chromosomes/DNA contained within, replication and transcription location, bounded by a nuclear envelope of two membranes separated by the perinuclear space.

Why are nuclear pores important?

Nuclear pores act as the link between cytoplasm and nucleoplasm, they help with compartmentalization in the eukaryotic cell and movement of mRNA, tRNA, and rRNA

What is an example of 1 pathway used for nuclear transport and what are the major players in it’s transport function?

The Ran/Importin pathway! Requires receptor proteins for import through the nuclear pore (importin) and a molecule to release the receptor protein from the protein being imported (Ran) and energy in the form of GTP. This process can either be Ran-dependent or Ran-independent.

What organelles give structure to the nucleus?

The nuclear matrix and lamina

What is the nucleolus and what differentiates it from the nucleus?

This is the ribosome factory of the cell, fibrils of the nucleolus co