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Telomeres

Protective end caps on chromosomes that help prevent important DNA from being lost during replication.

Genes

DNA regions that contain instructions for making a protein or a functional RNA such as tRNA or rRNA.

Promoters

DNA regions that help determine whether a gene is transcribed.

What happens at a promoter?

RNA polymerase binds there to begin transcription.

Why do cells make proteins?

Proteins provide structure perform enzymatic reactions build and remodel cell structures transport materials and send signals.

Central dogma

DNA is used to make RNA and RNA is used to make protein.

Transcription

Process in which DNA is used to make an RNA copy.

RNA processing

Editing of the initial RNA transcript into mature mRNA.

Translation

Process in which a ribosome reads mRNA and builds a protein.

Where does transcription occur?

In the nucleus.

Where does translation occur?

In the cytoplasm.

Initiation of transcription

RNA polymerase binds the promoter and separates the two DNA strands.

TATA box

A common promoter sequence where RNA polymerase can bind to begin transcription.

Template strand

The DNA strand read by RNA polymerase to make a complementary RNA strand.

RNA base-pairing rule for adenine

In RNA uracil pairs with adenine instead of thymine.

Elongation of transcription

RNA polymerase moves along the template strand and adds complementary RNA nucleotides.

What happens to DNA after RNA polymerase passes it?

The DNA strands rewind behind RNA polymerase.

Termination of transcription

RNA polymerase reaches a termination region and releases the RNA transcript.

What happens to the RNA transcript after transcription?

It must be processed before leaving the nucleus as mature mRNA.

How does mRNA leave the nucleus?

It exits through nuclear pores and enters the cytoplasm for translation.

What is a ribosome made of?

Ribosomal RNA and proteins.

What do ribosomes do?

They read mRNA and join amino acids into a protein.

Free ribosomes

Ribosomes in the cytosol that make proteins that function in the cytosol.

Bound ribosomes

Ribosomes associated with rough ER that make secreted proteins membrane proteins and proteins for certain organelles.

What determines whether a ribosome stays free or is directed to rough ER?

Whether the growing protein contains a signal sequence.

Signal recognition particle or SRP

A particle that binds a signal sequence on a growing protein and directs the ribosome to rough ER.

What happens after SRP directs a ribosome to rough ER?

The protein is made into or through the rough ER membrane.

What happens to the ribosome after translation of a rough ER protein ends?

It detaches from the rough ER and becomes a free ribosome again.

What happens to a newly made rough ER protein?

It can be modified and packaged in vesicles for transport to the Golgi apparatus.

Rough ER phospholipid synthesis

Rough ER helps synthesize phospholipids that can assemble into membrane bilayers.

Why is phospholipid synthesis near rough ER useful?

The cell can build membrane fragments containing phospholipids and membrane proteins.

Smooth ER main functions

It synthesizes lipids breaks down substances and stores materials.

Lipids made by smooth ER

Triglycerides cholesterol and steroid hormones in specialized cells.

Smooth ER in liver cells

It makes and packages triglycerides and cholesterol for transport to tissues.

What molecule is the starting material for all steroid hormones?

Cholesterol.

Major steroid-producing tissues

Testes ovaries and adrenal glands.

Smooth ER detoxification

Smooth ER in liver cells breaks down drugs alcohol and hormones.

Metabolites

Inactive breakdown products made when the liver processes drugs alcohol or hormones.

Why can drug tests detect substances in urine?

The liver makes metabolites that return to blood and are filtered by the kidneys into urine.

Glycogen

A large storage molecule made of many glucose molecules.

What can liver cells do with glycogen?

Store it break it down and release glucose into the bloodstream to help regulate blood glucose.

What can skeletal muscle do with glycogen?

Break it down and use the glucose for its own energy.

Why can skeletal muscle not release glycogen-derived glucose into blood?

It lacks the enzyme needed to release free glucose into the bloodstream.

Sarcoplasmic reticulum

Specialized smooth ER in muscle cells that stores calcium.

Why is calcium release from sarcoplasmic reticulum important?

Calcium release helps regulate muscle contraction.

Which muscle has the most developed sarcoplasmic reticulum?

Skeletal muscle.

Golgi apparatus

Stacked membranous sacs that receive proteins and membrane material from rough ER.

Cis face of Golgi apparatus

Receiving side that receives vesicles from rough ER.

Trans face of Golgi apparatus

Shipping side that sends finished products to their destinations.

Golgi apparatus functions

It modifies concentrates sorts and packages proteins and membranes into vesicles.

Why is the Golgi called the cell traffic director?

It sorts and sends processed materials to the plasma membrane organelles or outside the cell.