Biology 243 - Theme 2B

Front 1

Nucleotides

Back 1

DNA's subunits. Consists of three components: a 5-carbon sugar, a base, and one or more phosphate groups. The 5-carbon sugar and phosphate groups form the backbone of the molecule, with each sugar linked to the phosphate group of the neighbouring nucleotide. The bases sticking out from the sugar give each nucleotide its chemical identity. Each strand of DNA consists of an enormous number of nucleotides linked one to the next.
Phosphate group attaches to the 5' carbon. Base is attached to 1' carbon.

Front 2

Purines

Back 2

A nitrogenous base. Double-ring structures, adenine and guanine.
A--T
G---C

Front 3

Pyrimidines

Back 3

A nitrogenous base. Single-ring structures, thymine and cytosine.
T--A
C---G

Front 4

Nucleoside

Back 4

Combination of sugar and base

Front 5

Phosphodiester bond

Back 5

Covalent bond that connects one nucleotide to the next. Connects the 3' carbon of one nucleotide to the 5' carbon of the next nucleotide through the 5' phosphate group. It gives the DNA molecule polarity. The 5' end of the molecule differs from the 3' end of the molecule.

Front 6

DNA molecule form

Back 6

DNA is a double helix. Bases form hydrogen bonds with other bases, connecting two single stranded DNA molecules and making a double stranded DNA molecule that is helical. A forms two hydrogen bonds with T and G forms three hydrogen bonds with C.

Front 7

Antiparallel

Back 7

DNA strands in a double helix are antiparallel, which mean they run in opposite directions. So the 3' end of one strand is matched wight the 5' strand of the other strand, and vice versa.

Front 8

Base stacking

Back 8

Interactions between bases in the same strand. It is a stabilizing force and it occurs because the non polar, flat surface of the bases tend to group together away from the water molecules, and hence stack on top of one another as tightly as possible.

Front 9

DNA Base Sequences

Back 9

There is no restriction of DNA base sequences, which suggested that genetic information in DNA could be encoded in the sequence of bases along the DNA.

Front 10

Chargaff's Rule

Back 10

# of T = # of A
# of G = # of C
G + A = C + T

Front 11

Supercoils

Back 11

DNA molecules in prokaryotic cells do this. Happens when a circular molecular coils upon itself. Caused by enzymes known as topoisomerases tag cleave, partially unwind, and reattach a DNA strand, which puts strain on the DNA double helix. Supercoils then relieve the strain and help to preserve the 10 base pairs per turn in the double helix.

Front 12

Chromosome

Back 12

How DNA is packaged in the nucleus. Most DNA is linear in eukaryotic cells, and they form a chromosome.

Front 13

Chromatin

Back 13

A complex of DNA, RNA, and proteins that gives their structure.

Front 14

Nucleosome

Back 14

A beadlike repeating unit of histone proteins wrapped with DNA making up the 10-nm chromatin fibre

Front 15

Histone

Back 15

A protein that is rich in the positively charged amino acids lysine and arginine, which enables them to form ionic bonds with the negatively charged sugar-phosphate backbone of DNA. DNA wraps twice around this

Front 16

Evolutionarily Conserved

Back 16

Very similar in sequence from one organism to the next. Indicates that they serve an essential function and therefore have not changed much over time.

Front 17

Ribosomes

Back 17

Where proteins are synthesized. But since ribosomes contain no DNA, there must be an intermediary molecule by which the genetic information is transferred from the DNA to the ribosome. This turned out to be RNA.

Front 18

Brenner, Jacob, & Meleson Experiment

Back 18

Proved that RNA was the intermediate step from DNA to proteins. Used a virus that hijacks the cellular machinery to produce viral proteins. Shortly after infection and before viral proteins were made, the infected cells produce a burst of RNA molecules that correspond to the viral DNA.

Front 19

RNA World Hypothesis

Back 19

Since RNA has properties of both DNA & proteins, many believe that the first information storage molecule was RNA. It is also supported by the fact that RNA is essential in key cellular processes, including DNA replication, transcription, and translation.

Front 20

If RNA was the original information storing molecule, why do cells now use DNA and proteins to carry out other cellular processes?

Back 20

DNA is much more stable than RNA and proteins are more versatile, so it makes sense that life evolved from and RNA-based world to the one we live in now.

Front 21

Differences between RNA & DNA

Back 21

Front 22

RNA Transcript

Back 22

A piece of RNA that is complementary in sequence to the template DNA according to the base paring rules. Transcript is produced by polymerization of ribonucleoside triphosphate

Front 23

RNA polymerase

Back 23

Enzyme that carries out the polymerization. Adds successive nucleotides to the 3' end of the growing transcript. This means that the RNA transcript grows in the 5' to 3' direction

Front 24

Non-template Strand

Back 24

Stand of DNA that is not be transcribed

Front 25

Promoters

Back 25

Regions of DNA that typically have a few hundred base pairs where RNA polymerase and associated proteins bind to the DNA duplex. Many eukaryotic promoters contain a sequence similar 5'-TATAAA-3', which is known as the TATA box. The first nucleotide to be transcribed is generally around 25 base pairs from the TATA box

Front 26

Terminator

Back 26

Transcription continues until the RNA polymerase encounters a terminator sequence. It stops here and the transcript is released.

Front 27

Housekeeping Genes

Back 27

Products needed at all times in the cell, so transcription takes place continually.

Front 28

General Transcription Factors

Back 28

At least six of these are required at the promoter region for transcription to occur. They attract the RNA polymerase and its associated proteins to the site. The PNA polymerase complex responsibly for transcription of protein-coding genes is called Pol II

Front 29

Transcriptional Activator Protein

Back 29

Needed to start transcription. They bind to a specific DNA sequence known as an enhancer, and recruit a mediator complex of proteins which in turn interacts with the Pol II complex, and transcription begins.

Front 30

Transcription Bubble

Back 30

Separation in the DNA double helix so transcription can take place.
DNA enters the RNA Pol II through channel and is threaded out another channel via a structure that splits the strands apart, forming a bubble, so that ribonucleotides can assemble on the template strand. Another part of the enzyme forces the growing RNA out a different channel. As DNA travels through the RNA polymerase, the RNA transcript is elongated at the active site of the enzyme.