Cell Biology, Chapter 5

Front 1

What experiment proved that DNA and not protein was the hereditary material? How did they prove this?

Back 1

The Hershey-Chase experiment proved that DNA and not protein was the hereditary material but having viruses grown in radioactive sulfur (protein only) or phosphorus (DNA only) infect a bacteria, and then centrifuged it. They found that the bacteria contained only DNA was injected into the bacteria.

Front 2

What is the orientation of the complementary DNA strands with respect to each other? What is this configuration called?

Back 2

One complementary strand points up, and the other points down; this configuration is known as antiparallel.

Front 3

In what direction does DNA polymerase add nucleotides? Which bonds form first?

Back 3

DNA adds polymerase only to the 3' end. So, DNA grows in the 5'-3' direction. The H-bonds between the complementary bases forms first, and then the phosphodiester bond with the upstream nucleotide.

Front 4

What functional group is at the 5' end of a DNA strand, and what one is on the 3' end?

Back 4

The phosphate group is on the 5' end, and the -OH group is on the 3' end.

Front 5

What is the chemical basis of complementarity between bases? Why are GC bonds stronger than AT bonds? What is the biological significance of this? What must be true about the orientation of the bases for proper h-bonding to occur?

Back 5

The complementarity of the base pairs is enforced because each only H-bonds with one other. G-C has 3 h-bonds, while A-T has only 2. Because of this, GC-rich regions of DNA are especially resistant to degradation. For the h-bonds to form between the complementary bases, they must be arranged antiparallel to each other.

Front 6

What functional group sticks out from the DNA molecule? Why is this? What is the biological significance of this?

Back 6

The phosphate group sticks out from the DNA cylinder because it is charged, polar, and acidic. This is biologically significant because DNA-associated proteins called histones are basic so they can bind to these phosphate groups.

Front 7

What are the major and minor grooves? Why is this significant?

Back 7

The major and minor grooves are the large and small grooves of the DNA helix. This is significant because some proteins can only bind at the major groove.

Front 8

Besides hydrogen bonds and covalent bonds, what other forces hold together the DNA molecule? In what orientation do they exist?

Back 8

There are hydrophobic and van der waals forces that exist between adjacent but not complementary bases (i.e. the bases immediately up or down the chain). They run parallel to the cylindrical helix, and hold the bases together.

Front 9

What is the strict definition of a gene?

Back 9

A gene encodes information on the production of RNA; not necessarily protein, since some genes code for catalytic RNA and ribosomal RNA.

Front 10

What is a chromosome? When are the chromosomes visible? How do we visualize chromosomes?

Back 10

A chromosome is a long strand of DNA. Chromosomes are distinct and visible during cell division but not interphase. We can distinguish among the many chromsomes in a cell by fluorescently labeling each chromosome type.

Front 11

What is the relationship between genes, chromosomes, alleles, and loci?

Back 11

Genes are the unit of inheritance. Genes exist on chromosomes.The spatial coordinates of a gene on a chromosome is called that gene's locus. Each cell has a pair of identical chromosomes (i.e. homologous chromosomes). Each homologous chromosomes have different versions of the same gene on the corresponding loci; these two corresponding genes are called alleles.

Front 12

What are dominant and recessive alleles?

Back 12

Dominant and recessive alleles both correspond to a specific phenotype. If a dominant and recessive allele are at the same loci on homologous chromosomes, only phenotype associated with the dominant allele is observed.

Front 13

What is a gamete? What is true about the alleles in gametes?

Back 13

A gamete is a reporductive cell that has only one of each chromosome instead of a homologous pair. The genes on these unpaired chromosomes cannot be called alleles.

Front 14

How does chromosome number and morphology vary across species?

Back 14

The number and shape of chromosomes varies across species, and can even vary among closely related species.

Front 15

What 2 changes do the chromsomes undergo during cell division?

Back 15

The chromosomes are first REPLICATED, and then SEGREGATED.

Front 16

What 3 DNA sequence elements are required for the successful replication and segregation of chromosomes? Describe each one.

Back 16

1. Origin site for initiation of DNA replication- always at the specific region.
2. The centromere- DNA sequences that allow two chromatids to bind to each other.
3. The two ends, called telomeres.

With yeast, if you have these three things, you can put anything on the chromosome and it will still replicate successfully.

Front 17

What is a centromere?

Back 17

A centromere is a specialized sequence of DNA with "higher-order repeats". When the centromeres of two identical (different from homologous!) chromosomes touch, they will bind together. Kinetochores bind to the the centromere region.

Front 18

What is the difference between a chromosome and a chromatid?

Back 18

A chromosome can either be an individual DNA strand, or two identical DNA strands fused together at a centromere.

A chromatid is one of the two identical DNA strands attached by a centromere in the second type of chromosome I described above.

Front 19

What is the kinetochore?

Back 19

The kinetochore is the part of the chromosome that associate with the centromere, and then binds to the spindle microtubules that pull the sister chromatids apart

Front 20

What is the difference between the chromosomes at different parts of the cell cycle? How does this influence cell function?

Back 20

During interphase, the chromosome is diffuse, and during mitosis it is compact. When it is diffuse, it can be used for transcription, but when it is compact it is unusable in transcription.

Front 21

What is heterochromatin? What is euchromatin? How are they related?

Back 21

All DNA is coiled during mitosis. During interphase though, some DNA is coiled and other parts are uncoiled. Euchromatin is uncoiled and active (in transcription) during interphase. Heterochromatin is found in centromeres and telomeres, and is remains coiled during interphase.

Front 22

What is true about the organization of chromosomes during interphase in the nucleus?

Back 22

The chromosomes are roughly organized within the nucleus during interphase. They are not a tangled mess.

Front 23

What is the definition of chromatin? What is a nucleosome? From bottom up, what are the 5 levels of organization of chromatin?

Back 23

Chromatin = DNA + proteins. A nucleosome is considered the subunit of chromatin; it consists of little beads of DNA wrapped around histones.

1. Nucleosome "beads on a string"
2. nucleosomes packed together into a thick strand.
3. That thick strand doing hairpin loops that can be seen under a microscope.
4. These loops coalescing into what we see as a compact chromosome.

1.

Front 24

How does the cell control what DNA gets transcribed and what doesn't?

Back 24

Local modification of histones determines whether a given region of DNA will get transcribed. The close association of DNA and histones allows for the precise regulation of gene expression.

Front 25

See Professor Fath about last slide

Back 25

See Professor Fath about last slide.