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Microbio GCC shelly Thai > Genetics Part 1 > Flashcards

Genetics Part 1 Flashcards

1
Q

GENETICS

A

- is the science of heredity.

The study of genetics includes:

a. the study of what genes are
b. the study of how the genes carry information
c. the study of how genes are replicated and passed to future generations of cells or passed between organisms.
d. the study of how the expression of the genetic information within an organism determines the particular characteristics of that organism.

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2
Q

gene

A

is a segment of DNA (a sequence of nucleotides in DNA) that codes for a functional product, usually a protein (or rRNA, etc.)

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3
Q

Genotype

A

the genetic makeup of an organism.

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4
Q

Phenotype

A

the actual, expressed properties,
such as an organism’s ability to perform a
particular chemical reaction. The phenotype
is the manifestation of the genotype.

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5
Q

DNA Replication

A
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6
Q

What is the nature of DNA Replication?

A
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7
Q

DNA Replication steps 1-7

A
  1. When DNA replication begins, supercoiling of DNA is relaxed by topoisomerase or gyrase
  2. The two strands of parental DNA unwind and separate from each other in one small DNA segment after another by helicase. A replication bubble is formed.
  3. Proteins stabilize unwound parental DNA
  4. DNA polymerase, an enzyme, makes the new daughter strand. It can only add new nucleotides to the 3’ end of an existing strand; therefore, a short piece of RNA called an RNA primer starts the synthesis of the new DNA strand
  5. The RNA primer is synthesized using the enzyme Primase (RNA polymerase)
  6. Free nucleotides match up to the exposed bases of the single- stranded parental DNA by base complementation: T-A, C-G
  7. Once aligned, the newly added nucleotide is joined to the growing daughter DNA strand DNA polymerase.
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8
Q

DNA Replication steps 8-11

A
  1. Each replication bubble contains 2 replication forks. At each replication fork, there will be a leading strand and a lagging strand.
  2. The leading strand is synthesized continuously in the 5’ to 3’ direction (from a template parental strand running 3’ to 5’)
  3. The lagging strand is synthesized discontinously in fragments of about 1000 nucleotides (Okazaki fragments) which later are joined to make one continuous strand.

The lagging strand is also synthesized in the 5’ to 3’ direction; but moves in the opposite direction of the replication fork.

  1. The lagging strand will have many RNA primers, one per Okazaki fragment generated while the leading strand only has one RNA primer
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9
Q

DNA Replication 12-15

A
  1. The RNA nucleotides of the RNA primer are later digested away by the 5’ to 3’ exonuclease activity of the DNA polymerase.
  2. DNA ligase joins the discontinuous fragments together with covalent bonds to make a continuous lagging strand.
  3. As the replication fork moves forward, the parental DNA unwinds (by helicase) a bit further to allow the addition of the next nucleotides.
  4. Each new double-stranded DNA molecule contains one original strand (conserved) and one new strand, thus the process of replication is called semi-conservative replication.
    - DNA polymerase uses 3’5’ exonuclease activity to proofread during replication
    - Has an error rate of 1 in every 1010 bases
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10
Q

DNA Replication visual

A
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11
Q

Rate of DNA Replication:

A

~ 1,000 nucleotides per second in E. coli growing at 37oC.

  • Under optimal conditions, the cell can initiate multiple replication forks.
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12
Q

Central Dogma

A

The central dogma, originally proposed by Francis Crick, states that the
flow of the genetic information in a cell is always from DNA to RNA to protein.

• Exception: in systems such as retroviruses like HIV, 14 DNA can be made from RNA

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13
Q

Gene:

A

a segment of DNA containing the information for a single polypeptide chain or functional RNA (i.e. rRNA, tRNA,

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14
Q

Promoter

A

a sequence that determines transcription (RNA synthesis) initiation.

It is always located at the 5’ end of the strand that is identical to RNA of the transcribed region.
Contain specific sequences (usually 5-10 bp) that allow
RNA polymerase and transcription factors to bind.

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15
Q

Regulatory elements:

A

Sequences that are not promoter but can also regulate transcription.

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16
Q

Transcribed region:

A

sequence that is actually copied into RNA

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17
Q

Terminator

A

transcription termination sequence that is always located at the 3’ end of the transcribed region.

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18
Q

Cistron

A

an old name for a gene

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19
Q

Polycistronic

A

1 promoter directs synthesis of 1 mRNA that can be translated to more than one polypeptide

– Prokaryotic genes

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20
Q

Monocistronic

A

1 promoter directs synthesis of 1 mRNA that translates to only 1 gene

– Eukaryotic genes

21
Q

Prokaryotes gene structure

A

polycistronic genes are usually involved in the same biochemical pathway.

– Such an arrangement of genes in a functional group is referred to as an Operon

– Allows for simple regulation of the whole pathway

– 1 mRNA has many sites for translation to start

– Allows for more and faster translation

– Allow for fast growth

22
Q

Eukaryotes gene structure

A

monocistronic genes allow for more control/regulation

– Do not mind a bit of slowness

• Ex. Synthesis of Tryptophan requires 5 enzymes in both prokaryotes and eukaryotes

23
Q

Transcription

A
  • Transcription requires an enzyme called DNA- dependent-RNA polymerase and a supply of RNA nucleotides (A, U, C, G).
  • DNA-dependent-RNA Polymerase links the RNA nucleotides together to form the mRNA strand.
    • RNA synthesis: 5’ 3’
  • Only 1 strand of the 2 DNA strands serves as a template for RNA synthesis. This DNA strand is called the antisense strand.
  • The other DNA strand is called the sense strand → similar to mRNA strand.
24
Q

antisense

A

the 1 strand of the 2 DNA strands serves as a template for RNA synthesis.

25
Q

• Factor-independent termination

A

inverted repeats form hair-pin
– short string of A’s

  • Terminator is usually a G/C-rich sequence followed by an A-rich sequence.
  • An RNA:RNA stem loop forms (more stable due to G/C-rich in stem). This is followed by the formation of DNA:RNA hybrid via A-U pairing.
  • Release of RNA chain since A-U base pairing is less stable and is24 easily dissociated.
26
Q

Types of RNAs Produced in Cells

A

All cellular RNAs are synthesized by the transcription process.

mRNAs: messenger RNAs, code for proteins

rRNAs: ribosomal RNAs, form the basic structure of the ribosome and catalyze protein synthesis

tRNAs : transfer RNAs, central to protein synthesis as adaptors between mRNA and amino acids

27
Q

RNA Processing in Eukaryotes

A

In Eukaryotic cells, the RNA that is initially transcribed is referred to as the pre-mRNA

-The pre-mRNA must be processed to become the mature mRNA before it can be translated into protein by ribosomes.

  • Exon: sense sequence of gene
  • Intron: intragenic region; non-sense sequence of gene
28
Q

RNA Processing in Eukaryotes splicing

A
  1. 5’ Cap
  2. 3’ Poly(A) tail addition
  3. Splicing by spliceosome (RNA + protein)
29
Q

Exon

A

sense sequence of gene

30
Q

Intron

A

intragenic region; non-sense sequence of gene

31
Q

genetic code.

A

he rules by which the nucleotide sequence of a gene is translated into the amino acid sequence of a protein

The genetic code is universal (with some exceptions)

The genetic code is degenerate
- 61 codons for 20 aa (sense codons) and - 3 stop codons (non-sense codons)

32
Q

codons

A

The nucleotide sequence representing individual amino acids (or stop signal)

33
Q

anti-codon.

A

The sequence complementary to the codon

34
Q

The Genetic Code Is Non- Overlapping

A

-There are reading frames for each gene in a DNA strand. -The open reading frame is the one that codes for a protein.

35
Q

Decoding the information in mRNA:

A

tRNA is part of the decoder All tRNAs are about the same

length & structure

Contains 3 loops; one of the loop contains an anticodon region that complements the codon in mRNA.

An amino acid is covalently attached to the acceptor stem at the 3’ tail.

36
Q

How does a tRNA know which aa to bind to?

A

Amino acid covalently linked to tRNAs at the 3’ tail by the enzyme aminoacyl-tRNA synthetases

  • Each aminoacyl tRNA synthetase recognizes one particular amino acid and all tRNAs that recognize codons for that aa
  • ARS can proofread and remove incorrect aa; < 1/5000 error
37
Q

Three steps of translation

A
  1. Initiation - finding the start codon and assembling the ribosomal subunits
  2. Elongation - reading the mRNA sequence and polymerizing the addition of corresponding amino acids to growing polypeptide chain
  3. Termination - recognition of the stop codon and release of the new polypeptide
38
Q

3 Important Sites of Ribosome:

A

– A (aminoacyl) site
– P (peptidyl) site
– E (Exit) site

39
Q

Prokaryotic Translation: Initiation

What is the first amino acid?

A

A special tRNA is used to carry the methionine to the

start codonmethionyl-tRNAfmeth
– A formyl group (CHO) is added to the methionine – Blocks the amino end of a peptide
– Can bind to the P site

• Regular methionyl-tRNAmet is used for the elongation of the polypeptide chain

– Can only bind to the A site, not the P site

40
Q

Prokaryotic Translation: Initiation

How does a ribosome know where to start translation on an mRNA?

A

mRNA contains a ribosomal RNA binding sequence… Shine Dalgarno sequence

• This sequence base-pairs with the 16S rRNA of the small subunit.

41
Q

Prokaryotic Translation: Initiation

what happens After the small ribosomal subunit binds

step 1

A

then the tRNA brings in the first Met aa to the P site
-The large ribosomal subunit binds to the small subunit to form the ribosome

42
Q

Prokaryotic Translation: Elongation

Step 2

A
  • tRNA brings in another aa to the A site. The anticodon must complement the codon.
  • All subsequent tRNAs enter at the A site.
43
Q

Prokaryotic Translation: Elongation

step 3-4

A

-A peptide bond is formed between the two aas by peptidyl transferase (rRNA from 50S); it is a ribozyme

  • Ribosome translocates to the next codon along the mRNA - Free tRNA moves to the E site
  • A site is free to accept another tRNA-aa
44
Q

Prokaryotic Translation: Elongation

Steps 5-6

A

-Process of elongation continues -Requires a lot of energy

45
Q

Prokaryotic Translation: Termination

Step7

A
  • When ribosome moves to one of 3 stop codons (UAA, UAG and UGA), translation stops
  • The stop codons do not encode any a.a. so they have no corresponding tRNA; they are called nonsense codons
46
Q

Prokaryotic Translation: Termination

Step 8

A
  • Newly synthesized protein is released as the ribosome dissociates
  • POST-TRANSLATIONAL PROCESSING of the polypeptide chain:
  • Polypeptide undergoes some modificationfirst methionine is removed by an
    enzymatic action and the final
    polypeptide chain is formed
47
Q

Can transcription and translation occur simultaneously in Prokaryotes

A
  • In bacteria, ribosomes begin translating mRNA while the mRNA is being synthesized
  • Several ribosomes can translate one mRNA simultaneously
48
Q
A

Microbio GCC shelly Thai (6 decks)

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