Genetics Part II

Question 1

describe RNA’s structure

Answer 1

BASES:
- CYTOSINE
- GUANINE
- ADENINE
- URACIL (takes THYMINE’S PLACE)

SUGAR:
- RIBOSE

PHOSPHATE GROUPS

Question 2

what are the THREE TYPES OF RNA and their FUNCTIONS?

Answer 2

**these are all NECESSARY to DO PROTEIN SYNTHESIS

rRNA:
RIBOSOMAL RNA–part of the STRUCTURE of RIBOSOMES

tRNA:
TRANSFER RNA–functions as HELPTER to bring CORRECT AMINO ACIDS to RIBOSOME to build NEW PROTEINS

mRNA:
MESSENGER RNA–carries the CODE from DNA to RIBOSOMES–where PROTEINS ARE MADE

Question 3

describe TRANSCRIPTION. the importance of RNA POLYMERASE?

Answer 3

what is TRANSCRIPTION?
- the SYNTHESIS of COMPLEMENTARY STRAND of RNA from the DNA TEMPLATE
- only reads INDIVIDUAL GENES, not the ENTIRE GENOME

**DNA CANNOT BE READ DIRECTLY by the protein-making machine :(
- needs an INTERMEDIARY!!! which is mRNA

RNA POLYMERASE:
- uses DNA and basically copies/transcribes information into mRNA
- uses one of the DNA strands (template/antisense strand) as a TEMPLATE–creation of a COMPLEMENTARY RNA MOLECULE

Question 4

what are the THREE STEPS OF TRANSCRIPTION?

Answer 4

1. INITIATION
   - RNA POLYMERASE binds to a specific site on the DNA known as the PROMOTER
   - begins to UNWIND THE DNA STRANDS

PROMOTER:
a sequence of DNA that is RECOGNIZED by the RNA POLYMERASE–specific to that POLYMERASE

2. ELONGATION
   - where the RNA NUCLEOTIDES are now ADDED
3. TERMINATION
   - RNA SYNTHESIS continues on until the RNA POLYMERASE reaches a site on the end called the TERMINATOR

Question 5

definition of TRANSLATION

Answer 5

the process where the RIBOSOMES read the mRNA SEQUENCE and make a PROTEIN based on the SEQUENCE

nucleotide pairings —-> amino acids (within a PROTEIN)

Question 6

describe the GENETIC CODE

Answer 6

this is where mRNA begins to STORE INFORMATION about which AMINO ACIDS need to get incorporated into POLYPEPTIDE CHAINS to make a PROTEIN within form of CODONS

Question 7

definition of CODONS

Answer 7

groups of 3 nucleotides that code for a PARTICULAR AMINO ACIDS

• together create in sequence form the GENETIC CODE

Question 8

describe the possible COMBINATIONS within our GENETIC CODE + what is REDUNDANCY?

Answer 8

COMBINATIONS:
have over 64 POSSIBLE PERMUTATIONS/COMBINATIONS of these three letter nucleotide sequences that are made from our FOUR NUCLEOTIDES (A,C,G,U)

**ACTUALLY :o we only have 20 SOLID AMINO ACID CODONS (PRIMARY)–we just have NUMEROUS CODONS FOR VARIOUS AA’s
this is known as REDUNDANCY

CODONS/COMBINATIONS (61):
- code for actual AMINO ACIDS
(1 of them is our START CODON–MET-AUG)

NONSENSE CODONS (3):
- code for a STOP-CODON which signals the END OF A PROTEIN MOLECULE
- UAA
- UAG
- UGA

Question 9

describe tRNA and its role with ANTICODONS

Answer 9

tRNA:
specific RNA MOLECULES that help DECODE a MESSENGER RNA (mRNA) sequence into a PROTEIN

ANTICODONS:
sequence that can RECOGNIZE and BIND to the COMPLEMENTARY mRNA CODON–has an attached end with CORRESPONDING AMINO ACID

Question 10

define the SHINE-DELGARNO SEQUENCE

Answer 10

SHINE-DELGARNO SEQUENCE:
- specific RIBOSOME BINDING SITE
- ribosomes begin to BIND mRNA at this sequence– “reads” the CODONS and inserts the appropriate AMINO ACID

**again remember TRANSLATION starts at the AUG START CODON and its respective STOP CODONS

Question 11

describe the TRANSLATION PHASES

Answer 11

1. all components form together to start TRANSLATIONS
2. RIBOSOME is now ASSEMBLED–tRNA with the FIRST AMINO ACID starts at the AUG START CODON of mRNA (cont. as second tRNA begins to approach)
3. SECOND PAIRING OCCURS with second codon (mRNA) and second amino acid (tRNA)
   **AMINO ACIDS joined together by PEPTIDE BONDS within the P SITE
4. SECOND PAIRING MOVES into P (pairing) SITE, THIRD PARING MOVES into A (arrival) SITE, and FIRST PAIRING MOVES into E (exit) SITE :)

**cycle continues with each pairing and amino acids joining with PEPTIDE BONDS –until it eventually grows into a POLYPEPTIDE CHAIN

5. ribosome reaches a STOP-CODON–products of a new RELEASED POLYPEPTIDE which forms a PROTEIN

Question 12

describe what happens in terms of BACTERIAL (PROKARYTOIC) genetic coding

Answer 12

both TRANSCRIPTION and TRANSLATION occur at the SAME TIME–SIMULTANEOUSLY

Question 13

describe what happens in terms of EUKARYOTIC genetic coding

Answer 13

TRANSCRIPTION:
- this occurs within the NUCLEUS
mRNA has to go from NUCLEUS to CYTOPLASM

EUKARYOTIC GENES:
- have specific NON CODING REGIONS: known as INTERONS

RNA POLYMERASE–continues to transcribe with INTERONS within our PRIMARY RNA TRANSCRIPT

SPLICING:
- INTERONS are REMOVED and SPLICED OUT–in order to make final mRNA

Question 14

describe overview of REPLICATION, TRANSCRIPTION, and TRANSLATION

Answer 14

REPLICATION:
- purpose; MAKE IDENTICAL COPIES of DNA
- location; NUCLEUS (E), CYTOPLASM (P)

TRANSCRIPTION:
- purpose; MAKE RNA
- location; NUCLEUS/NUCLEOLUS (E), CYTOPLASM (P)

TRANSLATION:
- purpose; MAKE PROTEINS from RNA
- location; all within CYTOPLASM of the RIBOSOME

Question 15

definition of regulation of genetic expression

Answer 15

the production of protein from RNA

Question 16

definition of CONSTITUTIVE EXPRESSION

Answer 16

where EXPRESSION LEVEL is RELATIVELY CONSTANT (housekeeping genes)
- typically have most GENES within distinction > 60%
example: GLYCOLYSIS

**specific material that is always needed at a CONSTANT RATE within our BODIES

Question 17

definition of REGULATED EXPRESSION

Answer 17

expression level that VARIES UNDER DIFFERENT CONDITIONS

have TWO TYPES;
1. INDUCTION
induced–the product is not made until NECESSARY
2. REPRESSION
repressed–continuously makes product until UNNECESSARY

Question 18

definition of OPERONS

Answer 18

number of GENES that are CONTROLLED COLLECTIVELY by ONE PROMOTER
–often occurs PRIMARILY within PROKARYOTES

Question 19

describe the LAC OPERON

Answer 19

a type of INDUCIBLE OPERON–induced within the PRESENCE of LACTOSE
- has specific genes for the TRANSPORT and METABOLISM of LACTOSE

if there is GLUCOSE ABSENCE:
- allows for the EFFECTIVE DIGESTION OF LACTOSE (since glucose is the PREFERRED CARBON SOURCE)

Question 20

what are the THREE GENES within LACTOSE OPERON?

Answer 20

LAC Z:
beta-galactosidase; cleaves LACTOSE to GLUCOSE and GALACTOSE

LAC Y:
beta-galactosidase permase; enables TRANSPORT OF LACTOSE into the CELL

LAC A:
transacetylase

Question 21

describe CATABOLITE REPRESSION

Answer 21

**again reminder, GLUCOSE is the PREFERRED CARBON SOURCE for most bacteria

LAC OPERON:
use of a TWO PART CONTROL MECHANISM that ensures cell is producing the NECESSARY ENZYMES ENCODED by the LAC OPERON ONLY

CATABOLITE REPRESSION:
seen within PRESENCE OF GLUCOSE–has CATABOLITE ACTIVATOR PROTEIN (CAP) helps in the PRODUCTION OF LAC OPERON ENZYMES–system stays INACTIVE until further notice

IF GLUCOSE IS PRESENT–CAP IS NOW ACTIVE and ACTIVATES the TRANSCIPTION of the LAC OPERON

Question 22

describe the TRYPTOPHAN OPERON

Answer 22

a type of REPRESSIBLE OPERON –its own structural genes are TRANSCRIBED till they are TURNED OFF
- we have FIVE GENES involved witihin TRYPTOPHAN SYNTHESIS
- this has to be REGULATED; if we do have TRYPTOPHAN PRESENT–genes for TRYPTOPHAN SYNTHESIS are NOT EXPRESSED

Question 23

define EPIGENETIC CONTROL

Answer 23

the STUDY of CHANGES in the REGULATION of GENE ACTIVITY and EXPRESSION that are NOT DEPENDENT on GENE SEQUENCE

• CHEMICAL MODIFICATIONS to DNA

Question 24

define POST TRANSCRIPTIONAL CONTROL

Answer 24

a type of REGULATORY MECHANISM that STOPS PROTEIN SYNTHESIS after TRANSCRIPTION has OCCURRED

• occurs mainly within EUKARYOTES
• has SMALL SINGLE STRANDED RNA known as MICRO RNA (mina) (has around 22 NUCLEOTIDES
• binds to COMPLIMENTARY mRNA–forming actual DOUBLE STRANDED RNA and DESTROYS IT!!!!!!
• occurs during the DEVELOPMENT and accounts for CELL-TO-CELL DIFFERENTATION

BACTERIA:
has also SIMILAR SHORT RNAS within BACTERIAL CELL to cope with ENVIRONMENTAL STRESS