Bio111 Exam 2- Module 14- TAMU- Fletcher

Griffith's experiment (1928)

Studied Streptococcus pneumoniae and discovered the transformation of harmless bacteria into deadly strains.

Transforming principle

Substance transferred from heat-killed S strain to R strain bacteria, identified later as DNA.

Avery, MacLeod, & McCarty's conclusion (1944)

DNA is the genetic material, proven through enzyme treatment experiments.

Hershey & Chase experiment (1952)

Used radioactive labeling to show that DNA, not protein, carries genetic information in bacteriophages.

Chargaff's Rule

Found that in DNA, the amount of adenine equals thymine (A=T) and guanine equals cytosine (G=C).

X-ray crystallography

Technique used by Wilkins & Franklin to determine the double helix structure of DNA.

Watson & Crick's model of DNA

First 3D model of DNA, depicting the double helix structure with sugar-phosphate backbones and base pairs.

Components of DNA

Includes sugar (deoxyribose), phosphate group, and nitrogenous bases (A, T, G, C).

Double helix structure

Formed by two antiparallel strands and stabilized by base pairing (A-T, G-C).

Base pairing values

A pairs with T (2 hydrogen bonds) and G pairs with C (3 hydrogen bonds).

Nucleotide composition rule

A + T + G + C = 100%, e.g., if A = 30%, then T = 30%, G = 20%, C = 20%.

Histones

Positively charged proteins around which DNA wraps to form nucleosomes.

Nucleosomes

A structure composed of DNA wrapped around histone proteins, resembling 'beads on a string'.

Chromatin

Complex of DNA and proteins that packages DNA into the nucleus and regulates gene expression.

Euchromatin

Loosely packed chromatin containing active genes, visible during interphase.

Heterochromatin

Densely packed chromatin with inactive genes, typically found near centromeres and telomeres.

Leading strand synthesis

Continuous DNA synthesis in the 5’ to 3’ direction.

Lagging strand synthesis

Discontinuous DNA synthesis occurring in short Okazaki fragments, in the 3’ to 5’ direction.

DNA polymerase

Enzyme that adds nucleotides to the 3’ end during DNA synthesis.

End replication problem

Challenge in eukaryotic linear chromosomes where gaps are left at the 3’ end during lagging strand synthesis.

Telomeres

Repetitive noncoding DNA sequences at the ends of chromosomes that protect genes.

Telomerase

Enzyme that extends telomeres, active in stem and cancer cells, preventing chromosome shortening.

Mutations

Permanent changes in DNA sequence that can be beneficial, neutral, or harmful.

Proofreading by DNA polymerase

Mechanism during replication that fixes mismatched bases to prevent mutations.

Nucleotide excision repair (NER)

Mechanism to remove and replace damaged DNA sections after replication, often due to UV light.

Active telomerase

Enzyme found in germ cells, stem cells, and cancer cells that maintains telomere length.

Consequences of mutations

Permanent changes that may lead to diseases or cancer, depending on their nature.

Types of mutations

Include missense, nonsense, silent, and frameshift mutations, each affecting gene function differently.

Bases in DNA

Adenine (A), Thymine (T), Guanine (G), and Cytosine (C) form the genetic code.

Antiparallel strands in DNA

The two strands of DNA run in opposite directions, 5’ to 3’ on one strand and 3’ to 5’ on the other.

Hydrogen bonds in DNA

Connect complementary bases (A-T with 2 bonds, G-C with 3 bonds) to stabilize the double helix.

X-shaped pattern in DNA

Indication of the double helix structure observed in Franklin's X-ray crystallography images.

Repetitive DNA in telomeres

Sequences that provide protection to the ends of chromosomes from deterioration.

Stem cells and telomerase

Telomerase remains active in stem cells, allowing for unlimited division and maintenance of telomere length.

Inactive telomerase in somatic cells

Most somatic cells have telomerase turned off, leading to aging and eventual cell death.

Dynamic chromatin states

Euchromatin can convert to heterochromatin and vice versa, affecting gene expression.

Replication fork

The area where the DNA double helix unwinds for replication.

DNA's role in heredity

DNA contains the instructions for the development and functioning of all living organisms.