DNA LECTURE 1 BMOL20090

DNA is the molecule of

DNA is the molecule of

inheritance

1. Double Helix:

The two strands spiral around each other in a ?, ladder-like structure.

twisted

1. Double Helix:

This double-helical arrangement is held together by ? between ?.

hydrogen bonds

complementary base pairs

• Nucleotides:

The basic building blocks of DNA

• Each nucleotide consists of three components:

Deoxyribose Sugar, Phosphate Group, Nitrogenous Bases

• Deoxyribose Sugar: A ?-carbon sugar molecule known as deoxyribose forms the ? of each DNA strand.

The deoxyribose sugars ? with the phosphate groups in the backbone.

five

backbone

alternate

• Phosphate Group: Phosphate groups ? the deoxyribose sugars together, forming the ? of the DNA strand.

link

sugar-phosphate backbone

• Nitrogenous Bases: There are four types of nitrogenous bases in DNA:

• Adenine (A)

• Thymine (T)

• Cytosine (C)

• Guanine (G)

• The nitrogenous bases are ? to the deoxyribose sugar and project ? toward the ? of the helix. ? between these nitrogenous bases is a critical feature of the DNA molecule.

attached

inward

center

Base pairing

Base Pairing: The two DNA strands are held together by ? formed between complementary ? of ? bases.

hydrogen bonds, pairs, nitrogenous

Adenine (A) pairs with ,

thymine (T)

cytosine (C) pairs with .

guanine (G)

This complementary base pairing ensures that the two strands are ? and allows for the accurate ? of DNA during cell ?.

complementary

replication

division

1. Double Helix:

DNA is composed of two ? that are arranged in a double helix.

long strands

• Antiparallel Strands:

One strand runs in the ? direction , while the other runs in the?.

5' to 3' (5' end has a phosphate group), 3' to 5' direction (3' end has a hydroxyl group)

This antiparallel arrangement is essential for

DNA replication and stability.

• Antiparallel Strands:

the two DNA strands run in opposite directions,

Major and Minor Grooves:

These grooves provide sites for

the binding of proteins and other molecules involved in various DNA-related processes, such as transcription and DNA repair.

• Major and Minor Grooves: The ? structure of DNA gives rise to major and minor grooves along the molecule's ?.

helical

surface

• Twisting and Coiling:

DNA can twist upon itself and coil to form more ? structures.

This coiling is essential for packaging long DNA molecules into ?

compact

the confined space of a cell's nucleus.

Structure of DNA molecule

double-helix structure, Nucleotides, Base Pairing, Antiparallel Strands, Major and Minor Grooves, Twisting and Coiling

how DNA is packaged in bacteria

nucleoid, supercoiling, proteins, circular DNA, No Introns, plasmid

Nucleoid:

The nucleoid is a distinct region within the bacterial cell where the DNA is

concentrated.

Nucleoid

bacteria lack a ?, so the nucleoid is not enclosed by a? .

membrane-bound nucleus

nuclear membrane

Nucleoid

is an ? shaped region

irregularly

Nucleoid

located in the ? part of the bacterial cell.

central

Supercoiling:

Bacterial DNA is often maintained in a ? state.

highly supercoiled

Supercoiling is ,

the twisting of the DNA double helix upon itself

Supercoiling helps to ? within the limited space of the bacterial cell.

condense and package the DNA

Enzymes known as ? regulate the supercoiling of DNA.

topoisomerases

Proteins:

Bacterial DNA is associated with certain proteins, such as ? proteins or ? proteins .

histone-like, nucleoid-associated (NAPs)

These proteins help in ? the DNA.

compacting and organizing

While bacterial histone-like proteins are different from eukaryotic histones, they serve a similar function in DNA ?.

compaction

Circular DNA:

Most bacterial genomes consist of a single, circular DNA molecule known as a ?.

chromosome

circular DNA

This circular configuration ? the packaging of DNA in bacteria compared to the ? chromosomes found in eukaryotic cells.

simplifies

linear

No Introns:

Unlike eukaryotic DNA, bacterial DNA typically lacks introns, which are ? .

non-coding regions interspersed between coding regions in eukaryotic genes

NO INTRONS

This streamlined gene structure allows for a more ? use of space in the bacterial genome.

efficient

Plasmids:

Bacteria can also contain smaller, circular DNA molecules called ?.

plasmids

Plasmids are separate from the chromosomal DNA and can replicate ?.

independently

plasmids often carry genes that provide the bacterium with specific ? , such as ?

advantages

antibiotic resistance

the ability to metabolize certain compounds.

how DNA is packaged in eukaryotes

to fit into the small confines of the cell's nucleus using levels of organization to compact and condense long DNA molecules into a manageable structure.

Nucleosomes:

The --- level of packaging

first

Nucleosomes:

involves the ----- of DNA

wrapping

Nucleosomes:

involves the wrapping of DNA around ------

proteins

Nucleosomes:

involves the wrapping of DNA around proteins called -----

histones

Nucleosomes:

involves the wrapping of DNA around proteins called histones to form -----.

nucleosomes

Nucleosomes:

Each nucleosome consists of about ? base pairs of DNA wrapped around an ? of histone proteins.

147

octamer

Nucleosomes:

The histones are ? charged

positively

Nucleosomes:

The histones are positively charged and interact with the negatively charged ? groups of DNA,

phosphate

Nucleosomes:

The histones are positively charged and interact with the negatively charged phosphate groups of DNA, facilitating the ? and ? of DNA.

coiling

compaction

• Chromatin:

Nucleosomes are not evenly spaced along the DNA molecule but are separated by ?

linker DNA.

chromatin.

The combination of nucleosomes and linker DNA

Chromatin is the complex of DNA and proteins (primarily histones) that make up the ?.

chromosomes

Chromatin is the complex of

DNA and proteins (primarily histones)

chromatin can exist in two main forms:

Euchromatin, Heterochromatin

• Euchromatin:

a less condensed and more accessible form of chromatin.

Euchromatin is associated with ?.

actively transcribed genes

Euchromatin is often found at

the inner regions of the nucleus.

Heterochromatin:

a highly condensed form of chromatin that is transcriptionally inactive.

Heterochromatin: is typically found at ?

the periphery of the nucleus

Heterochromatin plays a role in

maintaining the structure of the chromosome

Chromosomes:

During ?, chromatin undergoes further condensation and compaction to form visible structures called chromosomes.

cell division (e.g., mitosis or meiosis)

Each chromosome consists of ? that has been tightly coiled and condensed. Humans have 46 chromosomes in most of their cells, with each pair containing one chromosome from each parent.

a single, long DNA molecule

Each chromosome consists of a single, long DNA molecule that has been ?.

tightly coiled and condensed

Humans have ? chromosomes in most of their cells,

46

each pair of chromosomes contains

one chromosome from each parent.

Higher-Order Structures:

Chromosomes can further ? and ? themselves into higher-order structures within the nucleus.

fold

organize

Higher-Order Structures:

These structures are not fully understood but are believed to play a role in

gene regulation and the spatial organization of genetic material.

The packaging of DNA into nucleosomes and higher-order structures not only serves to ? but also plays a critical role in ?.

compact the genetic material

gene regulation

The accessibility of DNA to various cellular machinery, such as transcription factors and RNA polymerase, is influenced by ?.

the degree of chromatin compaction

Euchromatin is more accessible for ?,

gene expression

heterochromatin is typically associated with

gene silencing.

Overall, the precise organization and packaging of DNA in eukaryotes are crucial for

the regulation of gene expression, the proper functioning of cells, and the accurate transmission of genetic information during cell division

The hierarchical organization of DNA packaging in eukaryotes includes:

nucleosomes, chromatin, Chromosomes, Higher-Order Structures:

Central Dogma \n Transmission of \n

genetic information

DNA to

TRANSCRIPTION

RNA

RNA to

TRANSLATION

Protein

TRANSCRIPTION to

TRANSLATION

Genetic information is

transmissible

Genetic information is transmissible example

Streptococcus pneumoniae

bacteriophages

viruses that infect bacteria

The Hershey-Chase experiment,

provided strong evidence that ?, not protein, is the genetic material responsible for ?

DNA

carrying and transmitting genetic information in bacteriophages (viruses that infect bacteria).

Phosphorus-32 labels 32P

DNA

Sulfur-35 35S labels

protein

overview of the Hershey-Chase experiment:

Experimental Setup:

1. Bacteriophages (T2 phage): Hershey and Chase chose to work with ?, a type of virus that specifically infects ? bacteria. The T2 phage consists of a ? and ? inside.

2. ? Labeling: To distinguish between DNA and protein, Hershey and Chase used two different radioactive isotopes as labels:

   • 32P (?): They used 32P to label the DNA in the T2 phage. This isotope labels the phosphate groups in DNA.

   • 35S (?): They used 35S to label the protein coat of the T2 phage. This isotope labels the sulfur atoms in proteins but not in DNA.

T2 bacteriophages

Escherichia coli (E. coli)

protein coat

DNA

Radioactive

Phosphorus-32

Sulfur-35

overview of the Hershey-Chase experiment:

Procedure: The experiment involved the following steps:

infection, blending and seperation, centrifugation

overview of the Hershey-Chase experiment:

1. Infection:

The T2 phages were allowed to infect E. coli bacteria

During infection, the phage ? its genetic material (either DNA or protein) into the bacterial cell.

injects

Centrifugation is a process that

separates substances based on their density, with heavier components settling at the bottom.

Results: The key findings of the Hershey-Chase experiment were as follows:

• When 32P-labeled DNA was used, the radioactive DNA was found ? the bacterial cells, indicating that the genetic material of the phage had entered the cells. This confirmed that DNA was the material responsible for carrying genetic information.

• When 35S-labeled protein was used, the radioactive protein remained ? the bacterial cells. This demonstrated that the protein coat of the phage did not enter the cells and was not involved in transmitting genetic information.

inside

outside

overview of the Hershey-Chase experiment:

Blending and Separation:

After a short period of time, the researchers used a blender to . ??

This was done to prevent ?

separate the protein coats of the phages from the bacterial cells

interference from unattached phage protein coats.

¤Nucleotides are the

building blocks of DNA/RNA

Structure of Nucleic Acids \n ¤Components \n ¤

5 Carbon sugar (pentose) \n ¤ Phosphate group \n ¤ Nitrogenous base/nucleobase (purine or pyrimidine)

Ribose and deoxyribose

carbons?

type of molecule?

play essential roles in

5

sugar/pentoses

the structure of nucleic acids

Ribose:

a component of .

It has the following structural features:

carbons?

Each carbon atom in the sugar ring is attached to a ?

ribonucleic acid (RNA)

5

hydroxyl group (OH).

deoxyribose is different due to

lack of OH group on C2

Phosphate group defined by

number of phosphates - mono,di,tri

what does 5’ mean in deoxyadenosine 5

’ triphosphate

5 prime, where the phosphate group is attached

bases

purines and pyrimidines

purine

adenine guanine

pyrimidine

cytosine thymine uracil