Biology: Transcription, Translation, and Gene Expression Processes, Organelles

Initiation of translation

The small ribosomal subunit binds to the mRNA and positions it at the start codon. The initiator tRNA pairs with the start codon in the P site, then the large ribosomal subunit joins, leaving the A site empty for the next tRNA, and protein synthesis begins.

Elongation of translation

The ribosome reads mRNA codons and pair them with tRNA anti codons which bring matching amino acids to the ribosome. tRNAs enter the A site, add their amino acid in the P site, then exit through the E site. The protein chain grows step by step.

Termination of translation

A stop codon reaches the ribosomes A-site and the polypeptide is released.

Central Dogma

The flow of genetic information within a biological system, summarized as DNA ⟶ RNA ⟶ Protein.

Gene

A segment of DNA that holds the instructions for building a protein.

Transcription

The process of creating messenger RNA (mRNA) from a DNA template, occurring in the nucleus.

Initiation of transcription

The step in transcription where RNA polymerase binds to the promoter region on DNA with the help of transcription factors.

Elongation in transcription

RNA polymerase moves along the DNA template strand, synthesizing a complementary mRNA strand from the DNA sequence.

Termination in transcription

RNA polymerase reaches a terminator sequence, signaling the end of transcription.

mRNA is released and moves on to processing, DNA rewinds into a double helix

DNA

The template containing the genetic information.

mRNA

The messenger RNA molecule, carrying the genetic code from the DNA to the ribosome.

RNA Polymerase

The enzyme that synthesizes mRNA from the DNA template.

Promoter

A specific DNA sequence where RNA polymerase binds to initiate transcription.

Terminator

A specific DNA sequence that signals the end of transcription.

Transcription Factors

Proteins that help RNA polymerase bind to the promoter and initiate transcription.

Coding Strand

The DNA strand that has the same sequence as the mRNA (except with T instead of U).

Template Strand

The DNA strand that is used as a template to create the mRNA.

5' Capping

The addition of a modified guanine triphosphate (GTP) molecule to the 5' end of the pre-mRNA to protect it from degradation.

Poly-A Tail Addition

The addition of a string of 100-200 adenine (A) nucleotides to the 3' end of the pre-mRNA to protect it and enhance translation.

RNA Splicing

The process of removing introns from the pre-mRNA and joining the remaining exons to form mature mRNA.

Introns

Non-coding sequences within a gene that are removed during RNA splicing.

Exons

Coding sequences within a gene that remain in the mRNA after splicing and are translated into protein.

Spliceosomes

Molecular machines that remove introns and join exons during RNA splicing.

5' Cap

A modified guanine nucleotide added to the 5' end of mRNA to protect it and help ribosome binding.

Poly-A Tail

A string of adenine nucleotides added to the 3' end of mRNA to protect it and enhance translation.

Translation

The process of synthesizing a polypeptide chain (protein) from an mRNA template. It occurs in the ribosomes.

A site

Aminoacyl-tRNA binding site: Where the tRNA carrying the next amino acid to be added binds.

P site

Peptidyl-tRNA binding site: Where the tRNA carrying the growing polypeptide chain is located, and where peptide bonds form.

E site

Exit site: Where discharged tRNAs exit the ribosome.

Ribosome

The cellular machinery where translation takes place.

tRNA

Has an anticodon that pairs with mRNA's codon and transfers amino acids to the ribosome during translation to build a protein.

Codon

A three-nucleotide sequence on mRNA that specifies a particular amino acid.

Anticodon

A three-nucleotide sequence on tRNA that is complementary to an mRNA codon.

Amino Acids

The building blocks of proteins.

Peptide Bond

The chemical bond that links amino acids together in a polypeptide chain.

Start Codon (AUG)

The codon that signals the start of translation and codes for methionine (Met).

Stop Codons (UAA, UAG, UGA)

Codons that signal the end of translation.

Mutation

Random change in the DNA sequence, caused by mutagens

Mutagens

something that causes a mutation

Substitute mutation

Switching one nucleotide for another

Only affects one codon

Causes no change to the number of nucleotides

Insertion mutation

Adding one or more nucleotides to DNA

Changes every codon at and after the insertion

"Frameshift"

Deletion mutation

Removes one or more nucleotides

Alters every codon at and after the mutation

"Frameshift"

Missense mutation

A change in a single codon that results in a different amino acid.

Frameshift mutation

A mutation caused by the insertion or deletion of a nucleotide that changes every amino acid after the mutation.

Silent mutation

A mutation that changes the DNA sequence but does not change the amino acid, because multiple codons can code for the same amino acid.

Nonsense mutation

A mutation that changes a codon into a stop codon, ending translation early and making a shortened or nonfunctioning protein.

Cell (plasma) membrane

Maintains homeostasis---allows things to move in and out of cell, is selectively permeable

Cytoskeleton

Maintain the structure of the cell

Centriole

Aide in cell division; arrange microtubules (only in animal cells)

Cytoplasm

Location where the organelles reside; gelatinous fluid

Cell wall

Surrounds the cell; Provides structure and support; prevents osmotic lysis (bursting of cell due to excess water)

Capsule

Polysaccharide outer layer of cell that helps prevent the cell from phagocytosis (the cell eating stuff)

Vacuole

Storage in Plants: water balance and waste; Storage in Animals: food and water

Lysosomes

Contains hydrolytic enzymes---breaks apart old organelles and other biomolecules with the use of chemical reactions involving water

Nucleolus

Region inside nucleus that makes ribosomes

Nucleus

Stores genetic information (nuclear envelope has pores and allows RNA and ribosomes to move out of nucleus)

Nucleoid Region

Region containing circular DNA; not membrane-bound.

Chloroplast

Site of photosynthesis: light energy is used to produce glucose

Mitochondria

Site of cellular respiration; where ATP is made (oxidative phosphorylation)

Ribosomes

Synthesize (makes) proteins

Rough Endoplasmic Reticulum

Transports proteins. Contains ribosomes which synthesize (create) proteins

Smooth Endoplasmic Reticulum

Synthesize lipids (phospholipids, steroids, hormones), detoxify toxins (alcohol and drugs)

Golgi Apparatus

Packages, modifies, and tags products like proteins and lipids for export

Transport Vesicles

Transports proteins/lipids from ERs to Golgi and to Cell Membrane

Pili

Hair-like appendage sometime used for movement; Often used in conjugation (exchange of DNA between bacteria)

Cilia

Hair-like structures used to transport fluid or materials past the cells; (not on coloring sheet for animal cell)

Flagella

Whip-like structure to help propel the cell (in animals, sperm only)

endomembrane system

A group of organelles in eukaryotic cells that work together to modify, package, and transport lipids and proteins.

These organelles have similar membranes (phospholipid bilayer) that allow them to interact.

Nucleic Acid

The virus's genetic material can be either DNA or RNA (but never both). It carries the instructions for making new viruses.

Capsid

A protein coat that surrounds and protects the nucleic acid. Made of repeating protein subunits called capsomeres.

Envelope

A membrane-like layer around some viruses, made from the host cell's membrane and viral proteins. It helps the virus enter host cells, protects it from the immune system, and contains glycoprotein spikes.

Step 1 of lytic cycle

Attachment. lytic cycle. The phage attaches to the surface of the host.

Step 2 of lytic cycle

Penetration. The viral DNA enters the host cell.

Step 3 of lytic cycle

Biosynthesis. Phage DNA replicates and phage proteins are made.

step 4 of lytic cycle

Maturation. New phage particles are assembled.

step 5 of lytic cycle

Lysis. the cell lyses, releasing the newly made phages

step 1 of lysogenic cycle

DNA Incorporation. The phage DNA becomes incorporated into the host genome

step 2 of lysogenic cycle

Host cell replication. The cell divides, and prophage DNA is passed on to daughter cells.

Step 3 of lysogenic cycle

Prophage excised. Under stressful conditions, the prophage DNA is excised from the bacterial chromosome and enters the lytic cycle. This phase can repeat until a stressor event.

Order of organelles in the endomembrane system

NUCLEUS→ROUGH ER→TRANSPORT VESICLE→GOLGI→TRANSPORT VESICLE→MEMBRANE

Phospholipid

amphipathic molecule w/ a polar head and non polar tails

Integral proteins

proteins that touch both polar + non polar parts of bilayer

Peripheral proteins

only on the outside of bilayer

-structual support

Cholesterol

aid in membrane fluidity + stability

Glycolipid

molecule made of a lipid (fat) attached to one or more sugars. It is found in cell membranes and helps with cell recognition, communication, and protection.

glycoprotein

protein with sugars attached. It helps cells talk to each other and recognize things.

olgiosaccharides

aid in cell communication

Is the majority of the cell membrane non-polar or polar

Non-polar

semipermeable

only lets certain molecules pass through it

What types of molecules can pass through the cell membrane

Small non-polar molecules

Whats an exception for the types of molecules that can pass through the membrane?

water, but it is very slow and ineffecient

Functions of integral proteins

Transport

Enzymes

Cell signaling

Enzymes

biological catalysts that speed up chemical reactions by lowering the activation energy

Passive transport

movement of molecules down the concentration gradient w/out using energy

diffusion

movement of molecules from an area of higher concentration to an area of lower concentration

types of passive transport

simple diffusion, faciliated diffusion, osmosis

simple diffusion

movement of molecules from high to low concentration w/out using a protein

what types of molecules are moved during simple diffusion

small non polar molecules

facilitated diffusion

molecules move from high to low concentration w/ the help of a protein

osmosis

diffusion of water