What is attached to the central carbon atom in an amino acid?
A carboxyl functional group, an amino functional group, and a side chain ("R group")
At the pH found in cells (about 7.0), what happens to the amino group on an amino acid?
It acts as a base and gains a proton, giving it a positive charge.
At the pH found in cells (about 7.0), what happens to the carboxyl group on an amino acid?
It acts as an acid and loses a proton, giving it a negative charge.
What type of interaction is directly responsible for the formation of secondary structure?
hydrogen bonds between sections of the polypeptide backbone
Difference between ribonucleotides and deoxyribonucleotides?
Ribonucleotides have a hydroxyl group bonded to their 2' carbon; deoxyribonucleotides have an H at the same location.
The condensation reaction that forms nucleic acid polymers occurs between a _____ group on one nucleotide and a _____ group on a second nucleotide.
Some viruses consist only of a protein coat surrounding a nucleic acid core. If you wanted to radioactively label the nucleic acids separately from the protein, you would use _____.
Franklin and Wilkins analyzed DNA by bombarding DNA crystals with X-rays. Their analysis yielded two numbers that sparked interest, 3.4 nm and 0.34 nm. What is the significance of these numbers?
These numbers tell us there are 10 rungs, or steps, on the DNA "ladder" for every turn of the helix
Why is it that RNA can catalyze reactions but DNA cannot?
The sugar of RNA is much more reactive than the sugar of DNA.
A nucleotide is composed of a(n) _____.
phosphate group, a nitrogen-containing base, and a five-carbon sugar
Similarities and differences between proteins and nucleic acids?
Proteins and nucleic acids both have a backbone and are formed by condensation reactions.
DNA molecules with a high percentage of guanine (G) and cytosine (C) are particularly stable. Why?
A G-C base pair has three hydrogen bonds, whereas an A-T base pair has two.
A feature shared by all monosaccharides?
In their linear forms, they all contain a carbonyl and several hydroxyl functional groups.
What is the difference between an aldose sugar and a ketose sugar?
the position of the carbonyl group
Which of the following linkages would you expect to find at a branch point in glycogen or amylopectin?
What is the major structural difference between starch and glycogen?
the amount of branching that occurs in the molecule
Enzymes that readily break starch apart cannot hydrolyze the glycosidic linkages found in cellulose. Why is this logical?
The geometry of the bonds is different, and the shapes of enzyme active sites are highly specific.
Peptidoglycan forms sheets that stiffen the cell walls of bacteria. How is the formation of sheets possible?
Individual strands are joined by peptide bonds-a type of covalent bond.
Both carbohydrates and fats are used as fuel in cells, but fats store twice as much energy per gram as carbohydrates. Which statement best explains why?
Fats have more C-C and C-H bonds with high free energy, and fewer C-O bonds with low free energy.
How the structures of fats, steroids, and phospholipids compare?
Fats and phospholipids contain glycerol, steroids do not.
Decreasing the saturation of the fatty acid chains on a particular type of phospholipid would result in the formation of _____.
more fluid bilayers
Which of the following phospholipid membranes would be most permeable to glycerol?
one with short and unsaturated tails
Steroid hormones are large communication molecules that are modified cholesterol molecules. How do you think they enter a cell?
Their lipid nature probably allows them to diffuse through the plasma membrane.
What is the most important factor in explaining why diffusion occurs spontaneously?
It leads to an increase in entropy.
What molecules can cross the lipid bilayer of a membrane directly, without a transport protein or other mechanism
lipids, carbon dioxide, water, oxygen
Which of the following statements would best describe a cell that has an extensive area of smooth endoplasmic reticulum?
It synthesizes large quantities of lipids.
Which of the following cytoskeletal proteins are important in changing cell shape or location (any type of cell movement)?
Microfilaments and myosin are among the cytoskeletal proteins important in cell movement.
Which statement most accurately describes what happens to proteins that lack an ER signal sequence?
They are released into the cytosol.
Where are the proteins that will be exported (excreted) from the cell made?
in ribosomes that attach to the endoplasmic reticulum
Scientists have found that polypeptides that are normally synthesized in the endoplasmic reticulum are about 20 amino acids longer when they are synthesized by ribosomes not attached to the endoplasmic reticulum. What is/are possible explanations for the greater length of these polypeptides?
The 20 amino acids serve as a signal sequence that directs the forming polypeptide to the endoplasmic reticulum, where they are cleaved off during processing.
Motor proteins require energy in the form of ATP. ATP hydrolysis results in a conformational change that allows the protein to move along microtubular tracks (pathways). What structural component of the motor protein contains the ATP binding site and, therefore, changes shape to enable movement?
the portion of the molecule that binds to the microtubular track along which the vesicle is being transported
Flagella and cilia bend or move, imparting mobility to cells. How do these structures move?
Dynein is a motor protein that hydrolyzes ATP and is responsible for movement of the cilium or flagellum.
To what does the 9 + 2 arrangement of microtubules, typical of cilia and eukaryotic flagella, refer?
the arrangement of microtubules within the axoneme
Which statement explains how pulse-chase experiments allowed researchers to study cells as dynamic enterprises—specifically looking at how molecules move inside cells?
By marking a specific population of molecules with a pulse of label, researchers were able to follow their fate over time.
Integrins are integral membrane proteins. They are often attached to _____.
cytoskeletal proteins and proteins in the extracellular matrix
How is phosphorylation important in a signal transduction cascade?
Phosphorylation will turn an inactive protein into an active one, which triggers another response in the cell.
A common GTP-binding messenger that links the receipt of an extracellular signal to the production of an intracellular one is _____.
Protein kinase is an enzyme that _____.
activates or inactivates other proteins by adding a phosphate group to them
When ATP is hydrolyzed into ADP and inorganic phosphate, _____.
a large amount of energy is released
The enzyme phosphofructokinase is the major regulatory enzyme of glycolysis. It catalyzes _____.
the phosphorylation of fructose 6-phosphate
In which metabolic pathways is substrate-level phosphorylation exhibited?
in both glycolysis and the Krebs cycle
A substrate-level phosphorylation occurs in the Krebs cycle when _____.
GDP is phosphorylated to produce GTP
The reactions of pyruvate processing, the citric acid cycle, and the electron transport chain occur within the _____ in the cell.
The first CO2 that is released during aerobic cellular respiration is _____.
between glycolysis and the Krebs cycle
C6H12O6 (glucose) + 6 O2 → 6 CO2 + 6 H2O
Where is most of the water in this reaction produced?
in the electron transport chain
The constituents of the electron transport chain have similar capabilities, with the exception of ubiquinone (coenzyme Q). What is different about ubiquinone?
Ubiquinone is lipid soluble and so can move through the inner mitochondrial membrane.
The chemiosmotic hypothesis is an important concept in our understanding of cellular metabolism in general because _____.
it explains how ATP is synthesized by a proton motive force
In fermentation the reactant _____ will get reduced and the reactant _____ will get oxidized.
pyruvate ... NADH
The proteins of the electron transport chain active in the light-dependent reactions _____.
are membrane proteins present in the thylakoid
Which statement is most accurate concerning how photosystem II (PS II) compares to the electron transport chain (ETC) of mitochondria?
In both systems, ATP is produced by chemiosmosis.
According to the Z scheme, what is the path of electrons through photosystem I (PS I) and photosystem II (PS II)?
PS II → pheophytin → plastoquinone → cytochrome complex → plastocyanin → PS I → ferredoxin
What important molecule that is needed for cellular respiration is released when water is split in the light reactions of photosynthesis?
During the Calvin cycle, carbon dioxide is _____, in order to drive the formation of sugars.
The light-independent reactions of plants function to make organic molecules using carbon dioxide as a carbon source. What is the electron source that helps reduce carbon dioxide to sugars and other organic molecules?
What is the main purpose of the light-dependent reactions of photosynthesis?
to produce NADPH and ATP
What would happen in a chloroplast containing an unusual form of rubisco that did not bind oxygen?
Photosynthesis would occur but photorespiration would not.
To increase the concentration of carbon dioxide available to the enzyme rubisco and minimize the degree of photorespiration, the CAM plants carboxylate _____.
During prophase a homologous pair of chromosomes consists of _____.
two chromosomes and four chromatids
Which term describes two recently replicated DNA strands that are joined together just before cell division?
The microtubule-organizing center found in animal cells is an identifiable structure present during all phases of the cell cycle. Specifically, it is known as?
In the process of chromosome separation, how do microtubules maintain contact with the kinetochores and shorten at the same time?
Motor proteins move chromosomes down the microtubular structures of the mitotic spindle.
MPF, or mitosis-promoting factor, consists of two important cell cycle regulatory proteins called _____.
cyclin and cyclin-dependent kinase (CDK)
Which event makes meiosis a reduction division and why?
separation of homologs in meiosis I because it produces 2 haploid (n) daughter cells from a single diploid (2n) parent cell
Crossover, the exchange of segments of homologous chromosomes, takes place during which of the following processes?
For the duration of meiosis I, each chromosome is _____.
two sister chromatids joined by a centromere
What is a major difference between eukaryotic DNA replication and prokaryotic DNA replication?
Prokaryotic chromosomes have a single origin of replication, while eukaryotic chromosomes have multiple origins of replication.
The Meselson-Stahl experiment was designed to answer which question?
What part of newly replicated DNA comes from the parental molecule and what part is newly synthesized?
In the polymerization of DNA, a phosphodiester bond is formed between a phosphate group of the nucleotide being added and _____ of the last nucleotide in the polymer.
the 3' OH
What catalyzes the formation of phosphodiester bonds between adjacent nucleotides in the DNA polymer being formed?
What provides the energy for the polymerization reactions in DNA synthesis?
the deoxyribonucleotide triphosphate substrates
What is true concerning DNA synthesis catalyzed by DNA polymerase?
The new DNA strand is synthesized in the 5'→3' direction; the template strand is read in the 3'→5' direction.
In the mismatch repair process, enzyme complexes replace bases that were incorrectly inserted into the newly synthesized DNA strand. To function, they must be able to distinguish between the parent DNA strand and the new strand. How is this accomplished?
The parent strand is methylated.
What are pyrimidine dimers?
adjacent pyrimidines on the same DNA strand that join by covalent bonding
What chemical force(s) stabilize(s) DNA's secondary structure?
hydrogen bonds and hydrophobic interactions
Srb and Horowitz showed that _____.
mutations of a single gene resulted in defects of one and only one enzyme
The idea that the sequence of bases in DNA specifies the sequence of bases in an RNA molecule, which specifies the sequence of amino acids in a protein, is _____.
the central dogma
What molecule serves as a link between the information-containing macromolecule, DNA, and protein synthesis?
What property of different sigma factors allows them to bind to different promoters?
different amino acid sequences resulting in different spatial arrangements of chemical groups
David Pribnow studied the base sequences of promoters in bacteria and bacterial viruses. He found two conserved regions in these promoters (the -10 box and the -35 box). What is the function of these two regions of the promoter?
They bind the sigma subunit that is associated with RNA polymerase.
During RNA processing a(n) _____ is added to the 3' end of the RNA.
a long string of adenine nucleotides
One function of polyribosomes is to _____.
increase the rate of polypeptide synthesis from a single mRNA
What is recognized by an aminoacyl tRNA synthetase?
one amino acid and the set of tRNAs that is coupled to that amino acid
Which of the following steps occurs last in the initiation phase of translation?
The large ribosomal subunit joins the complex.
How does the bacterial ribosome recognize where to start translation?
The small ribosomal subunit binds to a sequence in the mRNA just upstream of the start codon.