In this lesson, we’ll review the structure of the nucleus, its main functions of storing and copying DNA, and what it does specifically in plant cells. After completing the lesson, check your understanding with a quick quiz.
Imagine a special occasion in your life, maybe your Grandma’s birthday, when you will bring her flowers just to make her smile. Bright lilies and pink roses are her favorite and will make her day. These flowers were once living, and actually continue to live on your table until they wilt.
But what are these living decorations really made of? The answer is cells – plant cells to be specific. Plant cells are usually rectangular in shape with a thick, rigid cell wall on the outside. Inside the cell, a small circular compartment called the nucleus stores the cell’s genetic information, DNA.DNA, short for deoxyribonucleic acid, controls everything about the cell and ultimately the plant, from the pink flower petals to the number of stamens in the center of your lilies.
DNA is so important to plant and animal cells that the nucleus is specifically designed to keep it safe. Think of it like a safe for an important document. There are ways in and out of the safe when needed, but for the most part, the items you keep inside are safely tucked away.Plant cells aren’t the only ones with this special compartment. Animals and fungi also have a nucleus in their cells. The nucleus does pretty much the same thing in all these cells; the main difference is what’s in the DNA it holds.
Plant DNA has instructions for all types of unique plant structures, like chloroplasts to make food, stomata to let gases in and out of the leaves, and vascular tissue to transport water.For this lesson, we’re going to focus on the nucleus, not the DNA. To understand all the functions of the nucleus, let’s first look at the structure and physical properties of the nucleus.
Structure of the Nucleus
The nucleus is a central structure in the cell, enclosed by two membranes on the outside called the nuclear envelope. Small openings called nuclear pores dot the surface of the envelope. These structures act like gates, allowing only certain things in and out of the cell. Much like an exclusive government meeting, you must have the right credentials to get in and out of the nucleus.
These credentials are called nuclear import and nuclear export signals. For proteins and other structures to pass through the nucleus’ membranes, they must have these ‘badges’ to let the cell know they are cleared for entry or exit.Nucleoplasm is a thick, gel-like substance that fills the inside of the nucleus. Here we’ll find the nucleolus, which is responsible for making other cell structures called ribosomes.
Once formed, ribosomes reside in the cytoplasm of the cell, outside the nucleus.Remember how the nucleus is a safe for that important document, DNA? The nucleus packages DNA as chromatin, in the form of a thick, messy-looking ball of string. Although under the microscope it might look jumbled, chromatin is in fact highly organized. Let’s look at how the cell stores chromatin, the first job of the nucleus.
Chromatin is created by winding DNA in a specific pattern inside the nucleus. DNA coils around proteins called histones, creating a structure that looks like beads on a necklace. Next, imagine wrapping that necklace around your finger to create more coils; these coils become even larger coils. In this way, a massive amount of DNA can be easily stored in the tiny compartment of the nucleus. It is highly organized, allowing the nucleus to access it as needed. This brings us to the next job of the cell: copying DNA and creating another molecule called RNA.
Copying Genetic Information
Cells sometimes need to make a copy of their DNA during a process called DNA replication. When cells divide, each new cell needs an exact copy of the DNA so they can have these important instructions for cell function. The nucleus uses a protein called DNA polymerase to copy DNA. The chromatin then condenses even further, forming large pieces of DNA called chromosomes, which can be easily sorted between the two new cells.DNA is also copied on a regular basis to RNA, ribonucleic acid, through a process called transcription.
RNA is a short copy of DNA that codes for proteins, which cells need for structure and function. RNA is copied in the nucleus by RNA polymerase and then exported to the cytoplasm where ribosomes, the protein factories of the cell, read it and make the protein it codes for.RNA is also essential to the creation of ribosomes. Even though ribosomes hang out in the cytoplasm, they are made in the nucleus. The nucleolus makes the RNA needed for ribosomes which is then exported to the cytoplasm to assemble with proteins, resulting in fully functional ribosomes. Cells can have one, or many nucleoli, depending on how many ribosomes that cell needs.
All plant cells contain a nucleus, a structure that stores DNA and acts as a cell’s command center. It is surrounded by the nuclear envelope and is filled with nucleoplasm. The nuclear envelope contains nuclear pores which allow molecules with the appropriate nuclear import and export signals in and out of the nucleus. The nucleus stores chromatin, strands of DNA wound into tight coils around histone proteins. DNA is copied during DNA replication for new cells, as well as copied to RNA to make proteins in the nucleus.
Ribosomes are also made in the nucleus by the nucleolus and are exported to the cytoplasm.