Lecture 28

Question 1

Gene

Answer 1

a segment of DNA, a sequence of nucleotides, that codes for a functional product, usually a protein

Question 2

E. coli DNA has ______ base pairs, and is about _______ long - 1000x longer than the entire cell. However, the chromosome takes up only about ______ of the cell’s volume.

Answer 2

4.6 million base pairs
1mm long
10% of the cell’s volume

Question 3

What is the shape of a chromosome in bacteria? Also, how many are typically found, exceptions to this?

Answer 3

one single circular chromosome usually, but some genomes have multiple of these, some have linear + circular chromosomes.

Question 4

Where is the chromosome attached?

Answer 4

attached at one or several points to the plasma membrane

Question 5

How does the long chromosome fit into the cell?

Answer 5

supercoiling

Question 6

Supercoiling is a consequence of what enzymes?

Answer 6

the enzymes gyrase and DNA topoisomerase

Question 7

Bacteria are haploid organisms meaning what? Problems with this?

Answer 7

only one chromosome or one set of chromosomes

-any mutation in a gene is not masked or corrected by a second, normal copy of the gene

Question 8

In a haploid organism like bacteria, the _______ or the perceptible characteristics of the organism, reflects its ________, or genetic composition.

Answer 8

phenotype, genotype

Question 9

Diploid organisms exhibit a ________ , or normal, phenotype for any trait, even though their genotype might contain one mutant copy and one ______ copy of the gene responsible for the trait

Answer 9

wild-type

Question 10

DNA recombination. What does this recombination allow for?

Answer 10

involves the exchange of genetic material either between multiple chromosomes or between different regions of the same chromosome

-genetic diversity

Question 11

Bacteria do not undergo meiosis, however, they can undergo _______ (a type of sexual reproduction) where what happens?

Answer 11

conjugation, during which genetic material is transferred from one bacterium to another and may be recombined in the recipient cell

Question 12

The central dogma of molecular biology?

Answer 12

that DNA acts as the information source for constructing proteins. The sequence of bases in DNA is used to get the correct sequence of amino acids in proteins

Question 13

What is it called when DNA bases are converted into a working copy? DNA is converted into mRNA

Answer 13

transcription

Question 14

Information from the working copy is then used to direct the sequence of amino acids during protein synthesis. mRNA directs protein synthesis

Answer 14

translation

Question 15

How is DNA organized, and what is it made up of?
What is the backbone made up of – how are they held together?
How is the double strand held together? Between which nitrogenous base pairs?

Answer 15

DNA is made up of a polymer of nucleotides ATGC. DNA in the cell is a double-stranded helix.

The backbone is made up of alternating deoxyribose sugars and phosphates (held together by phosphodiester bonds)

The two strands are held together by hydrogen bonding between specific nitrogenous base pairs: AT and CG

Strand is antiparallel

Question 16

The antiparallel setup of DNA influences the DNA replication process because __________ can only add new nucleotides to the _______ end. This means that the two growing strands grow in ________ directions.

Answer 16

DNA polymerases
to the 3’ end

different

Question 17

DNA replication is semiconservative. What does this mean?

Answer 17

each new ds DNA molecule contains one original (conserved) strand and one new strand

Question 18

Replication is the process by which a cell copies its DNA prior to division. DNA in a cell must be ________ before the cell divides, so each ________ cell receivers the same genetic information.

Answer 18

duplicated, daughter cell

Question 19

OriC

Answer 19

the place on a bacterial chromosome where replication begins. this is called the origin of replication

Question 20

What does the OriC consist of? What initiation protein is it recognized by?

Answer 20

a specific DNA sequence of about 250 bases that is recognized by DnaA

Question 21

DnaA

Answer 21

binds to the OriC region, and opens up the double helix to expose individual strands to the replication machinery

Question 22

The zone of unwound DNA where replication occurs

Answer 22

the replication fork

Question 23

What is the direction of DNA replication in prokaryotes?

Answer 23

bidirectional

Question 24

The two loops following replication must be separated by?

Answer 24

the enzyme topoisomerase

Question 25

supercoiling is relaxed by?

Answer 25

topoisomerase or gyrase (which are also the enzymes that aid in supercoiling)

Question 26

double strand of DNA is unwound by?

Answer 26

helicase

Question 27

single strand binding proteins (ssbp)

Answer 27

• acts to stabilize single stranded DNA
• proteins that are added to the unwound single strand of DNA to prevent hydrogen bonding and reversion of the double helix

Question 28

after the replication fork has been exposed, then _______ primers (________) are established. After this _________ are added.

Answer 28

RNA primers (ribonucleotides)

deoxynucleotides

Question 29

The leading strand is synthesized _______, because? This means that mRNA is read from _______ but replication occurs from

Answer 29

continuously because there is always a free 3’ OH

3’ to 5’

5’ to 3’

Question 30

The leading strand is primed only once by ______, however the lagging strand is primed multiple times bc?

Answer 30

primase

primed multiple times because there is no 3’ OH readily available (for a nucleotide to attach) as it is on the opposite end of the replication fork

Question 31

The lagging strand is made in short segments called?

Answer 31

okazaki fragments

Question 32

what joins okazaki fragments?

Answer 32

DNA ligase joins them to make one continuous strand

Question 33

proteins/enzymes are encoded on DNA in the form of _______

Answer 33

genes. very little “junk” in prokaryotic genome

Question 34

three components of prokaryotic genes, and define each

Answer 34

promoter - where to start

coding sequence - the information we want

terminator - when to stop

Question 35

parts of the coding sequence that do not participate in the next step

Answer 35

leader and trailer sequence

Question 36

prokaryotic genes are often organized into _______. definition of this.

Answer 36

operons. operon = multiple genes grouped together into a single transcriptional unit, under the control of a single promoter

(genes encoding related enzymes are often clustered together)

Question 37

RNA polymerase proceeds through operons and transcribes the whole group of genes into a single, long mRNA molecule. What is this called? When this is translated, several proteins are made, one after another by the same ribosome. What is an example of this?

Answer 37

polycistronic mRNA (eukaryotes do not have this)

-the lac operon is an example of this

Question 38

By organizing genes into an operon (like the lac operon that controls lactose metabolism and is regulated by availability of lactose and glucose – contains three enzymes lacZ,Y and A)

by organizing the lac genes into an operon, _____

Answer 38

prokaryotes can allow for expression of related genes to be regulated under the control of one promoter. this means higher efficiency for the cell.