A&P Chapter 4

What did Miescher discover in 1869?

Nuclein in cell nuclei, now known as DNA.

three parts of a nucleotide

A sugar, phosphate group, and nitrogenous base.

pyrimidine bases

Cytosine, thymine, and uracil.

purine bases

Adenine and guanine.

DNA sugar

Deoxyribose.

What makes up the DNA backbone?

Alternating phosphate groups and deoxyribose sugars.

Which DNA bases pair together?

Adenine-thymine and guanine-cytosine.

How many hydrogen bonds connect A and T?

Two.

How many hydrogen bonds connect G and C?

Three.

What are A-T and C-G combinations called?

Base pairs.

What does complementary base pairing allow you to do?

Predict the sequence of one DNA strand from the other.

What is DNA's essential function?

To code for the proteins a cell synthesizes.

What is chromatin?

DNA complexed with proteins.

How many chromosomes are in human chromatin?

46.

How long would human DNA be if fully unwound?

About 2 meters.

nucleosome

A chromatin segment made of a core particle and linker DNA.

What is the nucleosome core particle made of?

Eight histone proteins with DNA wound around them.

How are nucleosomes arranged?

In a zigzag pattern that folds chromatin like an accordion.

How does chromatin become a chromosome?

The folded strand is packed into irregular loops and coils, before cell division.

What is a chromosome territory?

A region of the nucleus occupied by a chromosome.

What happens to chromosomes before cell division?

The DNA is copied and each chromosome becomes two sister chromatids.

What joins sister chromatids?

A centromere.

What is located on each side of the centromere?

A kinetochore.

What are the three types of RNA?

mRNA, rRNA, and tRNA.

How does RNA differ from DNA in strand structure?

RNA is single-stranded; DNA is a double helix.

What sugar does RNA contain?

Ribose.

Which base replaces thymine in RNA?

Uracil.

What is RNA's essential function?

To interpret DNA's code and direct protein synthesis.

What is a gene?

An information-containing segment of DNA that codes for an RNA molecule.

How many chromosomes come from each parent?

23.

What is the genome?

All the DNA in one 23-chromosome set.

About how many nucleotide pairs are in the human genome?

About 3.1 billion.

What did the Human Genome Project sequence?

More than 99% of the human genome.

What is genomics?

The study of a genome and how its genes and noncoding DNA interact.

How can one gene code for more than one protein?

Through alternative splicing of mRNA.

What are single-nucleotide polymorphisms?

Combinations of single-base differences that account for human genetic variation.

What is genomic medicine?

A branch of medical diagnosis opened by knowledge of disease-producing mutations.

What is a base triplet?

A group of three nucleotides coding for an amino acid.

What is a codon?

A group of three bases in mRNA.

How many possible codons are there?

64.

Why can some amino acids have more than one codon?

There are 64 possible codons but only 20 amino acids.

What is the start codon?

AUG.

What amino acid does AUG code for?

Methionine.

What do stop codons do?

End translation.

Do all cells use all of their genes?

No. A given cell uses only about one-third to two-thirds of its genes.

What happens when a gene is activated?

An mRNA copy is made and moves to the cytoplasm to be read by a ribosome.

What is transcription?

The process of copying DNA into RNA.

What enzyme performs transcription?

RNA polymerase.

What does RNA polymerase do?

Opens DNA, reads one strand, and assembles complementary RNA.

What signals RNA polymerase to stop?

A terminator sequence.

What is pre-mRNA?

The initial RNA containing exons and introns.

What are exons?

The 'sense' portions retained in the processed RNA.

What are introns?

The 'nonsense' portions removed from pre-mRNA.

What is alternative splicing?

A process that allows one gene to code for more than one protein.

What is translation?

Conversion of nucleotide language into amino-acid language.

What three components are needed for translation?

mRNA, tRNA, and ribosomes.

What does tRNA do?

Carries an amino acid to the ribosome.

What is an anticodon?

A three-nucleotide sequence on tRNA that pairs with an mRNA codon.

What are ribosomes made of?

A large and small subunit composed of rRNA and several enzymes.

When do ribosomal subunits come together?

During translation.

What are the three ribosome sites?

A site, P site, and E site.

What happens during translation initiation?

The ribosome assembles at the mRNA start codon and the initiator tRNA enters the P site.

What is the start codon recognized during initiation?

AUG.

What is the initiator tRNA anticodon given in the guide?

UAC.

What happens during elongation?

tRNAs bring amino acids and the ribosome builds the polypeptide chain.

Where does the next tRNA enter?

The A site.

Where does an empty tRNA exit?

The E site.

What is wobble?

Tolerance of some mismatches at the third base of a codon.

What does wobble allow according to the guide?

48 different tRNAs to pair with 61 amino-acid codons.

What happens during translation termination?

A stop codon is reached and the protein is released.

What binds the A site during termination?

A release factor.

Where do ribosomes dock when making proteins destined for secretion or lysosomes?

The rough endoplasmic reticulum.

What is a polyribosome?

A cluster of about 10-20 ribosomes translating one mRNA at once.

What is the overall sequence from gene information to protein?

DNA → RNA → protein.

What do chaperone proteins do?

Guide new protein strands into their proper configuration.

What are stress/heat-shock proteins?

Some chaperone proteins produced under stressful conditions.

What organelles are important in protein processing and secretion?

The ER and Golgi complex.

What is posttranslational modification?

Modification of a protein after it is assembled.

What coats the ER transport vesicles described in the guide?

Clathrin.

What does the Golgi complex do to proteins?

Modifies them further, often by adding carbohydrate chains.

What can Golgi vesicles become?

Lysosomes or secretory vesicles.

How do secretory vesicles release cell products?

By merging with the plasma membrane and releasing products by exocytosis.

What hormone begins the casein gene-regulation example?

Prolactin.

What happens after prolactin binds its receptor?

A regulatory protein is activated and moves into the nucleus.

What does the regulatory protein do in the nucleus?

Binds DNA near the casein gene.

How is casein ultimately released from the cell?

Golgi-packaged secretory vesicles release it by exocytosis.

How can regulatory proteins control gene transcription?

By attracting/positioning RNA polymerase or changing DNA accessibility.

Does DNA directly code for every substance made by cells?

No. It codes for RNA and proteins, which indirectly control synthesis of many substances.

Why is DNA replication necessary?

It is necessary before cell division.

What enzyme opens the DNA double helix during replication?

DNA helicase.

What is a replication fork?

The point where DNA is opened and its bases are exposed.

What enzyme adds complementary nucleotides during replication?

DNA polymerase.

What enzyme joins short DNA strands?

DNA ligase.

What is semiconservative replication?

Each daughter DNA molecule has one old helix and one newly synthesized helix.

What happens to histones during DNA replication?

New histones are synthesized in the cytoplasm and transported into the nucleus.

What is a mutation?

A change in DNA structure caused by replication errors or environmental factors.

Can some mutations have no effect on protein structure?

Yes.

What percentage of DNA does the guide say does not code for proteins?

98%.

What are the four main phases of the cell cycle?

G1, S, G2, and M.

What happens during G1?

The cell grows, makes proteins, performs its functions, and gathers materials for DNA replication.