Lesson 4: The nucleus

nucleus

both the repository of most of the cell’s genetic information and the control center for the expression of that information.

inner and outer nuclear membranes.

Inside the nucleus are the DNA-bearing chromosomes of the cell, separated from the rest of the cell by two membranes, called the _____. The two membranes make up the nuclear envelope.

Nuclear Envelope

A double membrane surrounds the nucleus, separating its contents from the cytoplasm

Nuclear Pores:

Channels in the nuclear envelope allow for the regulated transport of molecules, such as RNA, in and out of the nucleus.

Nucleoplasm

The fluid-filled space within the nucleus that contains the chromatin, nucleolus, and other structures.

Chromatin:

Thread-like structures made of DNA and proteins that form the chromosomes.

Nucleolus:

A dense region within the nucleus where ribosomes are synthesized.

• genetic material storage

• cell control

• DNA replication and Transcription (Central Dogma)

importance of Nucleus

genes

• Hereditary information is transmitted in the form of distinct units called __

• The fundamental units of heredity are made of DNA, containing instructions to build proteins or functional RNA molecules that determine traits, and regulate cell functions.

Johann Friedrich Miescher

• isolated nuclei from white blood cells obtained from pus found on surgical bandages. Extracting these nuclei with alkali led to the discovery of a novel substance that he called “nuclein,” which we now know as DNA

Eduard Zacharias

reported that extracting DNA from cells causes the staining of the chromosomes to disappear. Zacharias and others therefore inferred that DNA is the genetic material.

oswald Avery

• showed that DNA is the Genetic Material of Bacteria the transforming substance of Pneumococcus was DNA

Martha Chase and Alfred Hershey

• Showed that DNA is the Genetic Material of Viruses they concluded that DNA, not protein, had been injected into the bacterial cells; hence, DNA must function as the genetic material of phages.

rna

____ is the Genetic Material in some Viruses Some types of bacteriophages carry their genetic material as single-stranded DNA, and a much larger group of viruses carry their genetic material as RNA

semiconservative replication

One of the two strands of every newly formed DNA molecule is derived from the parent molecule, whereas the other strand is newly synthesized. This is called ____ because half of the parent molecule is retained by each daughter molecule

Kornberg and Thomas

• proposed that histone octamers are created by joining together two H2A-H2B dimers and two H3-H4 dimers and that the DNA double helix is then wrapped around the resulting octamer.

heterochromatin,

• Segments of chromatin so highly compacted that they show up as dark spots in micrographs are called ____

euchromatin

• whereas the more loosely packed, diffuse form of chromatin is called _____

karyotype

Unique banding patterns of chromosomes.

semi conservative replication

• Each new DNA molecule consists of one parental (original) strand and one newly synthesized strand

Meselson-Stahl experiment (1958).

•Process: • The parental double helix separates into two single strands. • Each serves as a template for the synthesis of a new complementary strand. •Result: • After the first cycle, both DNA molecules are hybrids (one old and one new strand). • After the second cycle, half are hybrid and half are completely new. •Significance: • This model was proven correct by the ____

conservative replication

This model was rejected because experimental evidence showed hybrid DNA after the first replication cycle.

Dispersive Replication

• Both DNA molecules produced contain intermixed segments of old and new DNA throughout each strand

Fluorescent in Situ Hybridization (FISH).

This technique allows for the detection of specific nucleic acid sequences in an intact cellular sample

Hybridization

A fluorescently labeled probe (a short strand of DNA or RNA) binds to a matching sequence on the target DNA or RNA.

reversible

This binding can be influenced by conditions like pH and temperature, allowing precise control over where and how the probe binds.