Cell Biology Review

Microbiology 3020c with John at University of South Florida

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By: Luke Wortham
Created: 2012-01-30
Size: 31 flashcards
Views: 13

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Prokaryotic vs. Eukaryotic Cells

Eukaryotes

* DNA enclosed in a membrane-bound nucleus

* Cells are generally larger and more complex

* Contain organelles

Prokaryotes

* No membrane-enclosed organelles

* No nucleus

* Generally smaller than eukaryotic cells

Ribosomes

Ribosomes: sites of protein synthesis

* Thousands of ribosomes per cell

* Composed of two subunits (30S and 50S in prokaryotes)

* S = Svedberg units

* Combination of rRNA and protein

Genome

A cell’s full complement of genes

Chromosomes

A circular DNA molecule called (Prokaryotes)

Major Chemical Elements in Living Organisms

Carbon, Hydrogen, Nitrogen, Oxygen, Phosphorus, and Sulfur

Plasmids

Small amounts of extra-chromosomal DNA that confer special properties ( i.e., antibiotic resistance)

Nature of covalent and hydrogen bonds

Covalent bond: strong bond between chemical elements where electrons, are shared equally between atoms

Hydrogen Bond

§Hydrogen bond: “weak” bond that forms due to electrostatic interactions between hydrogen atoms and more electron-attracting (electronegative) atoms

* Water

* Multiple hydrogen bonds impart considerable stability to molecules

Play major roles in the biological properties of proteins

Polar vs. non-polar covalent bonds

Polar

* Possessing hydrophilic (“water-loving”) characteristics

* Generally water soluble

Nonpolar

* Possessing hydrophobic (“water-repelling”) characteristics

* Not water soluble

Hydrophobic vs. Hydrophilic

Hydrophobic interactions

Weak bonds that occur when nonpolar molecules, or nonpolar regions of molecules, associate tightly in a polar environment

Play important roles in

* Enzymes binding substrates

* Protein conformation

* Stabilization of RNA and cell membranes

General Structure - Four Classes of Macromolecules - Protein

Proteins: polymers of amino acids

* Most abundant macromolecules in cells

* Found throughout cell

* Have important structural and enzymatic roles

Base pairings in DNA (which bases pair with which)

Adenine always pairs with Thymine

Guanine always pairs with Cytosine

purine and pyrimidine bases pair up (not the specific depictions of the molecules and bonds, just general nature of the interactions, hydrogen bonding, etc.)

Purine bases (adenine and guanine): contain two fused heterocyclic rings

Pyrimidine bases (thymine, cytosine, and uracil): contain a single six-membered heterocyclic ring

Difference between RNA and DNA (single vs. double stranded, different sugars)

DNA

Double-stranded, complementary

Strands held together by hydrogen bonds

RNA

Typically single-stranded

Demonstrates secondary structure (folding back upon itself)

Four classes: mRNAs, tRNAs, rRNAs, and small RNAs

Redox Reactions (which is oxidation, which is reduction)

Chemical reactions that transfer electrons between reactants

In oxidation, a substance loses electrons, or is oxidized

In reduction, a substance gains electrons, or is reduced (the amount of positive charge is reduced)

The electron donor is called the reducing agent.

The electron receptor is called the oxidizing agent.

Some redox reactions do not transfer electrons but change the electron sharing in covalent bonds. An example is the reaction between methane and O2.

Three Stages of Aerobic Respiration

Cellular respiration has three stages:

1. Glycolysis (breaks down glucose into two molecules of pyruvate)

2. The citric acid cycle (completes the breakdown of glucose)

3. Oxidative phosphorylation (accounts for most of the ATP synthesis)

Role of electron carriers (e.g. NAD⁺/NADH)

NADH passes the electrons to the electron transport chain

Unlike an uncontrolled reaction, the electron transport chain passes electrons in a series of steps instead of one explosive reaction

O2 pulls electrons down the chain in an energy-yielding tumble

The energy yielded is used to regenerate ATP

Proton Motive Force

H+ gradient across a membrane couples

* The H+ gradient is referred to as a proton-motive force, emphasizing its capacity to do work.

Fermentation vs. Aerobic Respiration

Fermentation: Pyruvate is converted to ethanol in two steps.

* No O2

Aerobic Respiration: O2 present

Central Dogma of Information Flow

Central dogma of molecular biology

* DNA to RNA to protein

Eukaryotes: each gene is transcribed individually

Prokaryotes: multiple genes may be transcribed together

What happens during DNA replication

* Helicase -> unwinds DNA

* Single-stranded binding proteins -> Stabilizes single stranded DNA

* Topoisomerase -> Relieves over-winding

* Primase -> Synthesizes RNA primer at 5' end

* DNA pol III -> Synthesizes DNA from DNA template

* DNA pol I -> Removes RNA and synthesizes DNA

* DNA ligase -> Joins DNA fragments

Transcription

Promoters: site of initiation of transcription

§Promoters are recognized by sigma factor of RNA polymerase

§Transcription stops at specific sites called transcription terminators

§Unlike DNA replication, transcription involves smaller units of DNA

§Often as small as a single gene

§Allows cell to transcribe different genes at different rates

Translation:

Translation: The process of proteins synthesis from RNA

Genetic code: a triplet of nucleic acid bases (codon) encodes a single amino acid

* Specific codons for starting and stopping translation

* Degenerate code: multiple codons encode a single amino acid

* Anti-codon on tRNA recognizes codon

* Wobble: irregular base pairing allowed at third position of tRNA

Functions of mRNA, rRNA and tRNA

mRNA (messenger RNA): encodes polypeptides

tRNA (transfer RNA): plays role in protein synthesis

rRNA (ribosomal RNA): plays role in protein synthesis

Negative Transcriptional Regulation (repression, induction)

Negative control: a regulatory mechanism that stops transcription

Repression: preventing the synthesis of an enzyme in response to a signal

*Enzymes affected by any repression make up a small fraction of total proteins in the cell

*Typically affects anabolic enzymes (i.e., arginine biosynthesis)

Induction: production of an enzyme in response to a signal

*Typically affects catabolic enzymes (i.e., lac operon)

*Enzymes are synthesized only when they are needed

*No wasted energy

Positive Transcriptional Regulation

Positive control: regulator protein activates the binding of RNA polymerase to DNA

Maltose catabolism in E. coli

* Maltose activator protein cannot bind to DNA unless it first binds maltose

Activator proteins bind specifically to certain DNA sequence

* Called activator binding site, not operator

Positive Transcriptional Regulation (continued)

Promoters of positively controlled operons only weakly bind RNA polymerase

Activator protein helps RNA polymerase recognize promoter

* May cause a change in DNA structure

* May interact directly with RNA polymerase

Activator-binding site may be close to the promoter or several hundred base pairs away

Operon

A cluster of functionally related genes can be under coordinated control by a single on-off “switch”

Operator: segment of DNA acting as the switch

Operon: the entire stretch of DNA that includes the operator, the promoter, and the genes that they control

General Structure - Four Classes of Macromolecules - Lipid

Lipids - know distinction between fats, phospholipids, and sterols

Lipids

* Polar compounds

* Have both hydrophobic and hydrophilic properties

* Play crucial roles as membrane backbones and as storage molecules

Sterols

* Rigid, planar lipids found in eukaryotic membranes

* Strengthen and stabilize membranes

General Structure - Four Classes of Macromolecules - Polysaccharrides

Polysaccharides

* Polymers of sugar units bonded together by glycosidic bonds

* Play important roles in cell walls and as storage molecules

General Structure - Four Classes of Macromolecules - Nucleic Acids

Nucleic acids: Polymers of nucleotides

*Two forms (RNA and DNA)

*[RNA]>>>[DNA]

About this deck

By: Luke Wortham
Created: 2012-01-30
Size: 31 flashcards
Views: 13

About StudyBlue

“I have been getting MUCH better grades on all my tests for school. Flash cards, notes, and quizzes are great on here. Thanks!”
Kathy