Cell Structure: Nucleus and Endoplasmic Reticulum

• Lab 5 covers Cell Structure

The Nucleus

• The nucleus stores genetic information as DNA
• DNA codes are the blueprint for all structure and function of the cell
• The nucleus is surrounded by a nuclear envelope, which has two membranes
• Inside the nucleus, DNA is organized into genes which specify a polypeptide
• A nucleolus is the location where ribosomal RNA (rRNA) is made
• Ribosomal RNA is a component of ribosomes

The Rough Endoplasmic Reticulum (ER)

• The rough ER buds out of nuclear envelope
• The rough ER is studded with ribosomes
• Ribosomes read mRNA and make proteins from the message
• mRNA is messenger RNA, a transcribed code of a gene
• When an mRNA binds to a ribosome, it heads to the rough ER to secrete a protein into the ER
• Modifications to the proteins are made in the lumen of the ER

The Smooth ER

• The smooth ER is continuous with the rough ER
• It has no ribosomes
• It synthesizes lipids like phospholipids and steroids
• It does additional protein folding
• It produces testosterone and detoxifies drugs

Golgi Apparatus and Lysosomes

• The Golgi apparatus comprises a stack of flattened saccules
• Think of it as the Transfer station/Post office of the cell
• The Golgi apparatus receives vesicles from the ER containing folded proteins
• It modifies molecules further within the vesicles
• It sorts and repackages molecules for their new destinations
• Lysosomes are vesicles that digest molecules or portions of the cell
• Lysosomes are like the garbage-man of the cell

Endomembrane System

• The rough ER synthesizes proteins and packages them in vesicles
• Transport vesicles contain products coming from the ER
• The Golgi apparatus modifies lipids and proteins
• The Golgi sorts and packages the lipids and proteins in vesicles
• Secretory vesicles fuse with the plasma membrane as secretion occurs
• The smooth ER synthesizes lipids and performs other functions
• Lysosomes digest molecules or old cell parts
• Incoming vesicles bring substances into the cell

DNA to RNA to Protein in Eukaryotes

• DNA goes through transcription, making RNA
• RNA goes through translation into an amino acid chain, then folding makes a protein
• DNA is housed in the nucleus
• RNA is transported to the ribosomes on the rough ER
• Ribosomes attached to the ER make polypeptides and release them into the ER, which is the 1st round of modifications
• Finally, a folded and modified protein is made in the smooth ER, and transported by the Golgi

Energy-Related Organelles: Mitochondria

• Mitochondria are bounded by a double membrane
• Their function is to break down carbohydrates to produce the energy molecule adenosine triphosphate (ATP)
• ATP is used in almost all metabolism reactions
• Mitochondria have their own DNA and ribosomes

The Cytoskeleton

• The cytoskeleton is a dynamic skeleton that gives cells shape
• It maintains cell shape, support, structure, and movement
• It is a network of interconnected protein filaments and tubules
• These consist of actin filaments, microtubules, and intermediate filaments

Cell Division: Centrioles

• Centrioles organize centers for microtubules during cell division
• They're best seen during mitosis
• Centrioles are only in animal cells, and not present in plant cells
• It is thought they play a role in mitosis