Cell Biology Exam 2

Dr. Campbell

DNA Polymerase Functions?

\-Reads template strands of parent DNA

\-Adds new nucleotides to growing DNA strand

\-Is self-correcting; can proofread and correct mistakes

What are the protein machines that replicate DNA?

\-__DNA polymerase__ | reads template strand and adds new nucleotides

\-__Primase__ | Synthesizes RNA primer

\-__Helicase__ | opens DNA double helix

\-__Single-Stranded Binding Protein__ | prevents reformation of base pairing prematurely

What are Mutations?

__Damage to DNA__

\-The only source of new genes

\-Caused by errors in DNA replication or accidental damage

\-May alter or inhibit DNA replication or Protein Synthesis

What are the steps to Excision Repair?

\-Excision | various enzymes cut out the damaged portion of the DNA

\-Re-Synthesis | DNA polymerase remakes the DNA based on a healthy strand

\-Ligation | DNA ligase - connects a newly made portion of the strand to the rest of the DNA strands; seals it up

Where is DNA located?

The majority of DNA is located in the Nucleus, but small amounts are found in the mitochondria and Chloroplasts.

How is information stored in DNA molecules?

information is stored in the sequence of Nucleotides in DNA

What are Chromosomes made of?

\-Chromosomes are made of chromatin

\-Chromatin is made of DNA and proteins

What direction does DNA polymerase write?

5’ to 3’

Protein Synthesis Steps

\-Replication (DNA)

\-Transcription (RNA)

\-Translation (PROTEIN)

What is mRNA?

Messenger RNA

\-Directs the synthesis of Proteins

Where does Transcription occur?

In the Nucleus (sometimes in Mitochondria and chloroplasts)

Where does Translation occur?

In the cytosol (sometimes in Mitochondria and chloroplasts)

What are the types of RNA synthesized and what happens after they are synthesized?

\-mRNA (messenger RNA) | carries the message of how to make protein; processed in nucleus prior to export

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\-tRNA (transfer RNA) | Exported from Nucleus to cytosol

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\-rRNA (ribosomal RNA) | Exported from Nucleus to cytosol, forms part of ribosome

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various others

How is RNA polymerase different from DNA polymerase?

\-does not require a primer

\-does not proofread

\-has a far greater error rate

\-performs multiple activities

\*Opens DNA helix

\*Adds RNA nucleotides

\*Closes DNA helix

\*Makes a single copy of RNA

where does RNA polymerase bind to the DNA at?

The promoter sites

How is mature mRNA formed?

\-primary mRNA capped on 5’ end w/nucleotide

\-Polyadenylation is added to 3’ end

\-the Primary mRNA undergoes splicing

what is an Exon?

protein coding region shorter than intron

what is an Intron?

Non-coding region

What is a spliceosome?

catalyst for splicing reactions

What are ribozymes?

Catalytic RNA molecules

What is a codon?

sequence of 3 mRNA nucleotide bases

What is the Start codon?

AUG - Methionine amino acid

What is the Stop codon?

UAA, UAG, UGA

What makes up ribosomes?

RNA + Protein - 2 subunits

What happens once translation is completed?

\-Ribosomal subunits separate

\-Polypeptide Release

\-**mRNA degraded** | so that mRNA will not bind to another ribosome and make more protein

What are Post Translational Modifications (PLMs)?

The process required for a polypeptide to become a fully functional protein

What is a Gene?

A unit of heredity containing the instructions that dictate the characteristics or phenotype of an organism

How is gene Expression determined?

Gene expression is primarily controlled at the level of transcription, largely as a result of binding of proteins to specific sites on DNA

How is Gene Expression Regulated?

DNA>RNA>Protein

\-Cell Type

\-Developmental Stage

\-Environment

Where is Gene Regulation shut down at?

Transcriptional control

What are Operons?

Cluster of genes transcribes as single mRNA common in bacteria

What does the membrane surround in the cell?

\-the entire cell

\-surrounding organelles (nucleus, lysosome, and ER)

\-Inside certain organelles (Mitochondria and Chloroplast)

What are the major functions of membranes?

\-Barriers | regulates what goes in and out of the cell

\-Cell Signaling | passes information about environment or other cells

\-Energy Metabolism | important proteins inside the membrane that aids in ATP synthesis inside the mitochondria.

What is the Fluid Mosaic Model?

The idea that the phospholipid bilayer is covered in proteins discovered by Singer and Nicholson in 1972

What are the 3 most common lipids?

\-Phospholipid | Most abundant lipid

\-Sterols | very common in animal cells (Chlesterol)

\-Glycolipids | sugar attached to a hydrophilic head

What is Membrane fluidity?

Movement of lipids in the bilayer

\-Rotating (Most common)

\-Exchanging with adjacent lipids

\-Flip flop between bilayer (Rarest)

What increases Membrane fluidity?

\-being an unsaturated chain (Bent)

\-Being a shorter chain

\-no cholesterol

\-Increase in temperature

What decreases Membrane fluidity?

\-Being a saturated chain (non bent)

\-Being a longer chain'

\-Having cholesterol

\-Decrease in temperature

What are the important membrane proteins?

\-__Transporters and Channels__ | allow passage of larger molecules across membrane

\-__Anchors__ | Keep cells together

\-__Receptors__ | receive messages, generates intracellular responses

\-__Enzymes__

What are porins?

Very large transmembrane channels formed by Beta sheets.

What are Aquaporins?

Channel within membrane that can be formed by alpha helices

Is the inside of channels hydrophobic or hydrophilic?

hydrophilic

What two carbohydrates are membrane proteins?

\-__Glycoproteins__ | short sugar chains attached to protein

\-__Proteoglycans__ | proteins with long chain polysaccharides attached

What are the functions of carbohydrates that are membrane proteins?

\-Protection

\-Identification (blood types)

\-Adhesion

What is a Thylakoid membrane?

A membrane with photosynthetic pigments that absorb light

What happens if you bleach the membrane of a cell?

Proteins move within the membrane to put it back to normal

How does passive transport work in the membrane?

passive transport is driven by diffusion because of the electrochemical gradient (Membrane potential + Concentration gradient)

What are the two major classes of Membrane transport proteins?

Channels - only passive

Transporters - passive & active

What are gap junctions?

two channel proteins that allow transport between two cells

What are three examples of ion channels?

__Voltage-gated channel__ | Membrane potential (electrical charge builds up causing it to open or close)

__Ligand-gated channel__ | ligand binding (something binds to the channel causing it to open or close)

__Mechanically gated/stress-activated channel__ | Mechanical stress, pressure, force, etc. cause the channel to open

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What is the Patch-Clamp experiment?

heating a glass pipette and stretching it to receive a very fine point and filled with solution in order to remove a patch of membrane from the cell

What is membrane potential?

result of unequal distribution of ions across the membrane (produces electrical signal when ions cross)

What are the three active transport pumps?

__Gradient-Driven Pump__ | Concentration gradient as source of energy

__ATP-Driven Pump__ | ATP provides energy to transport ions

__Light-Driven Pump__ | uses Retinal pigment to change shape of protein (mainly in plants and bacteria)