U2T3 - Keywords

Question 1

Purine bases

Answer 1

Larger, double ring structure. Adenine + guanine.

Question 2

Pyrimidine bases

Answer 2

Smaller, single ring structure. Thymine (Uracil in RNA) + cytosine.

Question 3

mRNA

Answer 3

Messenger RNA. Single chain twisted into helix, length + base sequence varies. Formed in nucleus by copying part of DNA (1 gene). Formed during transcription. Carries code for gene from nucleus to ribosomes in cytoplasm. Short life, involved in protein synthesis.

Question 4

tRNA

Answer 4

Transfer RNA. Small molecule, single strand of RNA in clover leaf shape. 20 types, each carry diff AA. Anticodon at mid point, complementary to codon on mRNA. Requires ATP to attach to AA. Transport AAs within cytoplasm for protein synthesis + ensures each mRNA codes for particular AA, aligning codons + AAs.

Question 5

rRNA

Answer 5

Ribosomal RNA. Large complex structure made in nucleolus. Forms over half mass of ribosomes.

Question 6

Anticodon

Answer 6

Sequence of 3 bases in middle of tRNA, determines which AA attaches by lining up against appropriate codon on mRNA in protein synthesis. Brings AA’s to correct position on mRNA during translation.

Question 7

Gene

Answer 7

Length of DNA which gives instructions for making 1 polypeptide.

Question 8

Sense/Coding/Template Strand

Answer 8

Strand of DNA where code is stored in molecular structure. The strand which is copied by mRNA during transcription.

Question 9

Triplet Code

Answer 9

20 diff AAs used to make proteins. Triplet code of 3 bases per AA produces 64 combinations 2 would give only 16). Each AA coded for by a codon.

Question 10

Codon

Answer 10

Sequence of 3 DNA bases which code for an amino acid.

Question 11

Degenerate Code

Answer 11

Multiple triplets of bases can code for same AA. First 2 bases are most important in determining which AA is coded for so mutation which substitutes 1 base for another may not alter the AA.

Question 12

Non-Overlapping Code

Answer 12

Code read in discrete groups of 3 bases, no overlap in coding sequences.

Question 13

Universal Code

Answer 13

DNA base triplets code for same AA in all organisms, allowing for development of gene technology so genes from one organism can be inserted into another species.

Question 14

Gene Mutation

Answer 14

Involves change in sequence of DNA bases of gene + may lead to change in AA sequence of polypeptide. May alter the way protein functions + so disrupt metabolic pathways (CF)

Question 15

Transcription

Answer 15

Copying DNA base sequence in mRNA in nucleus.

Question 16

Translation

Answer 16

mRNA info translated into AA sequence in cytoplasm.

Question 17

Intron

Answer 17

Non-coding DNA sequences. Some may regulate gene expression.

Question 18

Ribosome

Answer 18

Small, free in cytoplasm/attached to ER. Contains large + small sub-unit, made of protein + rRNA. Has 2 binding sites for tRNA molecules. A (aminoacyl) + P (peptidyl) In translation, ‘A’ site binds aminoacyl-tRNA as directed by codon. ‘A’ site only works once first aminoacyl-tRNA has attached to P site. ‘P’ site codon occupied by peptidyl-tRNA which carries already synthesised AAs. ‘E’ site occupied by empty tRNA as about to exit ribosome

Question 19

Peptidyl-tRNA

Answer 19

tRNA with multiple AA’s attached as long chain.

Question 20

Epigenetics

Answer 20

Study of heritable modifications in the genome. Change in phenotype, rather than genotype as doesn’t change sequence, just extra bits added onto DNA. Can enhance or stop expression of gene.

Question 21

CpG Island

Answer 21

CpG sequences grouped. If critical num islands methylated, DNA switched off + transcription can’t happen.

Question 22

Genetic Code

Answer 22

The way DNA codes for specific amino acids in specific positions in a polypeptide.

Question 23

Central Dogma of Molecular Biology

Answer 23

DNA replication cycle -> Transcription to RNA -> Translation to protein. However, retroviruses have reverse transcriptase to reverse transcription.

Question 24

Epigenetic Modifications

Answer 24

Edits/extra bits added to genes which don’t change DNA sequence.

Question 25

Histone Modification

Answer 25

Short term epigenetic mod. DNA wrapped round bundles of 8 histone proteins, modified by adding chem groups. Affect frequency/likelihood of transcription.

Question 26

Exon

Answer 26

Segment of DNA/RNA molecule containing info coding for protein/peptide sequence.

Question 27

DNA Helicase

Answer 27

Separates double stranded DNA into single strands, allowing each strand to be copied.

Question 28

RNA Polymerase

Answer 28

Synthesises RNA by following strand of DNA. Copies DNA sequence into RNA sequence during transcription.

Question 29

Aminoacyle (A) Site

Answer 29

Binding site on ribosome for charged t-RNA molecules during protein synthesis.

Question 30

Peptidyl (P) Site

Answer 30

Second binding site for tRNA in ribosome.

Question 31

Start Codon

Answer 31

First codon of mRNA translated by ribosome. Starts translation for protein synthesis.

Question 32

Stop Codon

Answer 32

Final codon in mRNA transcript, signals termination of translation into proteins.

Question 33

Peptide Bond

Answer 33

Chemical bond between 2 molecules when carboxyl group of one reacts with amino group of other, releasing water molecule.

Question 34

Central Dogma

Answer 34

Theory in genetics subject to several exceptions that genetic info is coded into self replicating DNA + undergoes unidirectional transfer to mRNAs in transcription.

Question 35

Reverse Transcription

Answer 35

Reverse of normal transcription. Nucleotide sequence copied from RNA template during synthesis of DNA molecule.

Question 36

DNA Methylation

Answer 36

Methyl groups added to DNA molecule. Can change activity of DNA segment without changing sequence. Often represses gene transcription.

Question 37

Frameshift Mutation

Answer 37

Base deletion. Means all subsequent codons are affected.